Tuesday, 29 September 2009

More postponement

Cheered by my recent board assembly successes, I wanted to rush ahead and assemble at least one of the remaining motherboard or extruder controller boards today. No such luck.

I had ordered these as complete kits (from Makerbot), so I got out all of the pieces for the motherboard. When I had ordered this, it was the most up-to-date version, so I duly had the webpage open for the most up-to-date version of the motherboard, 1.2. Something seemed wrong; I didn't have all the parts. So I re-checked, and I had ordered version 1.1!
After this false start, I was checking all the components, and I still didn't have all the parts! I am missing five 1.8 k ohm resistors and one red LED, and the IC1, the RS485 communication chip. But I have 5 excess 472 resistors, and a spare green LED!

Moving on to the extruder controller, I am missing a 180 ohm resistor. Also, the eight 100 nF ceramic capacitors, the two 16 pF ceramic capacitors and the two 0.22 uF ceramic capacitors are all packaged in pairs in unlabelled packaging, so I have no idea which is which! Not helpful.

I have used the "Contact us" facility on the Makerbot store website to request the missing parts and some advice or perhaps new labelled parts? for the confusing capacitors.

So for now, I can't work on either board.

Three step(per)s forward

I "fried" the last stepper motor driver board last night, and touched it up in a couple of places and removed solder balls before hand-soldering the rest. I cleaned it and checked it this morning, plugged it in and it all works. Now I have a triplet of boards at last. Yay!

Although I can understand the routing of the circuit on the boards themselves, I still haven't learnt much about the circuit diagrams. I know that the white dots on the board denote the negative ends of the LEDs, because I worked out the negative end of the circuit diagram, and I now know that VC+ is the 12 V supply to the board and that VCC, the voltage common collector, is the adjusted voltage, which is 5 V on this board. I came to realise that the arrow heads on the diagram don't have anything to do with direction of electron flow
or what is thought of as current; they just mean this part of the circuit carries on somewhere else! Oh, and I now know the symbols for LEDs, resistors, variable resistors, electrolytic and ordinary capacitors. And that's about it.

But I don't know how to count the pin numbers on the chip, for example. And I am confused by the power LED on this circuit - on my boards it is connected straight from the 5 V leg of the voltage regulator, and yet the diagram places a capacitor before it, either an electrolytic or ceramic, depending on which route you take.

Hmm, that really doesn't look like what's actually in front of me.

........................................unless this (below).......................really means this
(below)?
And if so, why wasn't it drawn like that for clarity?


Finally, as promised, a costings update:

Farnell sub-total from separate orders = £54.88
  • A3982 driver chip, part number 1521717, £4.60 and
  • chip-leg cutter, part number 7256449, £39.90, combined VAT of £6.68
  • IDC header, straight, 10-way, £1.61 each (x 2), VAT of £0.48
No P&P.

Running total (excluding set of washers and screws from B&Q) = £487.51

Monday, 28 September 2009

Boarding school, term 3. Muddling through the end of year tests....

Hoorah! Hooray! Yippee! Wonderful! Marvellous! Brilliant! Fantastic! (Can you tell I'm happy?)

After a whole week of head-scratching, web browsing, and advice from my brother, my partner and Nophead, I have finally FIXED my bad stepper motor driver board. Unfortunately, this was the board with near-perfect soldering, of which I was very proud. Now it looks a mess! Anyway, here is the proof it works:

OK, it's not pretty.

The voltage regulator had been tested whilst still fixed to the board (but only by its ground pad). The regulator was definitely faulty. Unfortunately, once I'd removed that, everything else in the 5V path gave readings of zero ohm when tested on a 20 k ohm setting on the multimeter with the +ve probe on the path and the -ve probe on the ground pin of the Molex-style connector. This meant there was a short to ground somewhere, still.

The first thing I checked was the power-indicating LED, as this was what I had replaced twice, once because the first one was dead (although it turned out that that was incidental to the board not working), and once because I checked it for correct orientation when the board still didn't work. The result was that this part of the circuit certainly didn't look tidy, and was a cause for suspicion. I cleaned it very carefully and checked the gap between it and its protective resistor, but it looked separated. I wondered if I had damaged the pad on the board, but without disconnecting it from the circuit there was no way to check.

Next candidate was the damaged track alongside the regulator's space. I decided to cut the track close by the 5V pin' pad,so I scraped off the protective Araldite I had applied, and scraped back to the copper track. Then I very carefully cut the track, and made sure there was no continuity across the cut. Now, using the diode setting on the multimeter, I could light the power LED, so that side of the circuit was sound.
I cut the track in a similar way towards the rear of the regulator's space. Checking on resistance setting 20 k ohm again, the part of the track alongside the regulator gave reading of 1 against ground, meaning no connection to ground, ie no short there.
O.K., they were my top candidates! And they were fine. And I now had 2 unnecessary cuts in my track!

Oh well, nothing ventured, nothing gained.....
Following the track, it goes from the regulator to the electrolytic capacitor from where it splits, with part then heading to the 100 nF ceramic capacitor and to the second RJ45 socket, and the rest going down a "via" under the electrolytic capacitor and off to various other parts of the board.
In order to test this, I cut the track in a clear section underneath the board. Testing the chip end of the circuit to ground, the meter gave 1.
Ah-ha, now the problem is narrowed down to 2 capacitors, the "via" or the RJ45 socket.

The RJ45 socket seemed unlikely to have a problem, and ditto the large capacitor. Having plenty of spare 100 nF ceramic capacitors, thanks to supplies from Nophead after I cracked (a different) one on this board right at the start, I decided to simply swap it.
Some little desoldering and resoldering later, and voila! we have readings of 1 from everywhere on the 5V path to ground. So the problem WAS the capacitor.

Now my problem was the breaks I'd deliberately put in the track....
First I used the conductive pen to fill in the gap in the track on the underside of the board. It takes 10 minutes to get conductivity through the "ink", and testing afterwards showed I had good conductivity between the copper ends.
Unfortunately, when I tried this on the top of the board, I found that I also had re-shorting to ground! Obviously the cuts on the upper side of the board reached the ground connection in the board. So, using a trusty cocktail stick (which should also be added to the parts requirements!) I could paste Araldite (ditto) into the cuts in the copper track, but while that dried, I used the conductive pen to rejoin the breaks going around the cut section. If the conductive pen only works temporarily, I shall solder wires between the track breaks.

Then I soldered a new voltage regulator in place, with the help of Blu-Tack, again. Unfortunately, I knocked the electrolytic capacitor loose, causing more burning plastic due to access issues with my soldering iron as I fixed it back on. I tested it, and the voltage regulator, and then resoldered the first (removed) RJ45 socket. I tested everything exhaustively.

And now we have Blackpool at Christmas! (For those non-UKers, that means all the lights came on.)

My partner thought the board was a gonner. I thought if it didn't work anyway, there was nothing to lose by trying to resuscitate it, and it was going to take another 3 weeks to order a fresh board from the States anyway. And it works.

(PHEW!)

Saturday, 26 September 2009

Switching the lights on

I swapped back to "playing" with my believed-to-be working stepper motor driver board. Looking back, I found Nophead's comment about connecting the enable pin to 0V in order to get the indicating LEDs working. I established from the instructions that the enable pin was pin 5 on the IDC socket, but I didn't know which was pin 5.

After some internet hunting, I eventually managed to confirm the identification of the pins relative to the ribbon cable wires. I thought. I tried that, and got nothing. Hmmm. After some more hunting, I found that my reference website had been wrong - but they're in good company, as Asus apparently got it wrong in their manuals and on their own website! Luckily, this being a communication type connection rather than power, nothing drastic happened when I'd connected the wrong pin.

Using this website, I got the right diagram.
Wire 1 on the ribbon cable goes to pin 1 on the IDC, which is at the end of the row adjacent to the tab on the male connector, shown here as on the top left of the connector, and pin 5 is marked with a wire.


In order to test the stepper motor driver board's indicating LEDs, the pin on the board's connector corresponding to pin 5 on the ribbon cable is connected to ground.
Here is a photo' showing the connector pins 5 (enable) and 9 (ground) linked with a wire.



After arranging this, I plugged in and switched on power to the working board - sure enough the LEDs lit, but one green on one side and one red on the other. Is this correct? Anyone know which ones are supposed to light up?

Friday, 25 September 2009

Second term at boarding school!

Just when you think you've got everything settled..........

.....My brother pointed out that just because I wasn't measuring 5V out of the voltage regulator whilst it was connected in circuit on the stepper motor driver board didn't mean it wasn't working; with a short-circuit anywhere in the 5V section of the circuit, the current would flow straight to ground, meaning no voltage to measure. However, there were no obvious shorts, no solder bridging two components and I had previously checked that all the resistors apart from the 0.25 ohm ones were sound. After Nophead's advive on checking low value resistors, I noted that my multimeter read 0.5 ohm when the probes were touched together on the lowest resistance range setting, 200 ohm. The resistors gave a reading of 0.8, meaning they are rated at ~0.3 ohm, which is about right allowing for slight inaccuracy of the meter at such low levels compared with range setting.
In circuit, there was no reliable way of measuring the capacitance of any of the small capacitors, so I was going on guesswork that the problem still lay, in fact, with the regulator.

I desoldered one pin on the regulator, and then the other.
I am getting on fine now using the solder braid with flux drawn onto it from a pen. This helps the solder to reflow. I placed the braid onto the top of the pin, acrosswise if possible, and applied the soldering iron tip on top of the braid for a few seconds. I found it easiest to position the braid and hold it in exactly the right orientation, with no twisting etc, with my hand, but once held in place by the soldering iron, I swapped to holding the braid with tweezers so that I didn't burn my hand when it got hot. Access was awkward, and I decided to desolder one of the RJ45 connectors to reduce the amount of melting and burning plastic where the large screws on the soldering iron shaft would catch! I still caught the edge of the Molex connector from time to time. I cut off the used end of desoldering braid holding the absorbed solder and repeated with clean and freshly-fluxed braid until the regulator's pins looked to be clear of solder. The pins still seemed tacked to the board, possibly with sticky burnt flux, so I cleaned around them and prised them up off the board. The pads below are fine.
Desoldering the through-hole pins of the connector was easier, still, after cutting the end of the braid into a point and using the fine iron tip, pressing the braid slightly down and into the hole as the solder wicked up.

Next I tried to desolder the regulator's large ground pad - that was just too tough! I managed to remove most of the solder, but there was some visible under the centre of the pad, but the gap between the part and the board was too thin (top to bottom) to be able to slide the desoldering braid in, and although I could melt some of it, because of the proximity of other components I couldn't use the big flat soldering iron tip, which would have been ideal to melt the lot all at once and allow the regulator to be released.
Eventually my partner went for the brute force option! and created more damage than was intended! Some of the board's contact pad lifted clean away, but the remainder still has contact to ground, and there is damage to the green coating over the track that leads from the 5V pin adjacent to the side of the regulator. There still seems to be continuity everywhere (there should be), though, so I have Araldited a thin protective layer over the shiny copper that is visible.
We tested the removed regulator - it is most definitely dead! Luckily, the minimum order for these had been 5, when I (thought I) needed 3, so there are a couple of spares after all (which is a relief because this was the part that came from RS, who were absolutely useless, and from whom I have no wish to order again)!

My brother rang just as all this was done, and said that I could test this board before putting another regulator on (just in case there is still a short on the board as well) by connecting the working board to power, and connecting a 5V contact on that board to a 5V contact on this board, and a ground contact on that board to a ground contact on this one. The regulator on the first board should easily be able to handle the current for both boards together. At least the power LED should come on for both boards. And if I do Nophead's thing of getting the other LEDs to work, too, I should get proper indication on both boards as well if this board is working. I need to look that up again, but meanwhile I'm letting the Araldite cure.

Thursday, 24 September 2009

Boarding School

I had advice (again) from Nophead (again) to forego the desoldering braid for removal of the dead chip on the first stepper motor driver board, and to cut the legs off as high, i.e. as close to the chip body, as possible. This I did - with the end legs, anyway, but I couldn't find anything fine enough to fit between and cut the other legs. After considering what was available that would definitely do the job with limited manoeuvre room, I decided to buy a chip-leg-cutter. You never know, I may need it in future.
This did the job well. When I lifted the broken chip off the board, a portion of the green board coating came away with it, exposing the copper underneath. The patch didn't extend to any of the pads. Carefully, I coated this with a thin protective layer of Araldite.
This was ancient - I got it in 1991, when I worked for the company! The lids were pretty stuck on, so that trying to unscrew them from the tubes resulted in highly twisted tubes, but putting some grip onto the lids worked. It is good to have some glue you know is still going to work years after first being opened.

Nophead's advice to brush the cut chip legs away with the soldering iron tip worked a treat. Each leg came away easily, and I wiped it from the iron. I used the flat tip to flatten the remaining solder on each pad, and put a thin line of paste along the row of pads on each side before soldering the new chip in place. The right way round!

I checked for bridges, and there were only bridges across legs that are connected with the trace anyway, so I didn't remove those bridges. I checked that there was continuity where there should be, and a lack of continuity where there should be, comparing with the working board. I checked the resistors, and they were all fine, too.

So I plugged in. Oops, no power LED and a very slight smoky smell. I switched straight off.
I took the power LED off, and checked it. Using my new flux pen to wet the component side of the desoldering braid, I was able to remove the solder quite easily. The LED had been fitted the right way around, and it still worked, so I soldered it back on. Hmm.

Since then, I have spent 2 days checking, rechecking and generally scratching my head. I checked all the vias going from top to bottom and did notice a couple without shiny metal rings like the working board has. At the stage I noticed, I didn't know what "vias" in electronics were!
I inserted the probe from my multimeter into the tops of the holes, and turned it around a few times. A thin green film came off, revealing shiny metal once more. I checked there was continuity between the top and bottom, and made sure there was for all such vias.

I checked the resistance for all the resistors, and they were all as rated. The only ones I couldn't check were the 0.25 ohm ones because my meter only went down as low as 200 ohm on its lowest setting.

At this stage, still scratching my head, I posted for more advice on the forum, specifically if the voltage regulator could be checked, and how.

I talked to my brother, who works in electronics, as he happened to 'phone, and he advised that I should check anywhere that a trace has been placed between the pads for a surface-mount component, because there may be a short here. I knew there were a couple of these on the boards, so I checked these, too. No problems found. He also suggested checking every pin, on the headers having 2 rows, against its neighbours. So I did that. No different from the working board. He also recommended connecting the power supply via a 12V bulb rated for 5 or 6 W to the board. If the board were shorted, the bulb would light more brightly compared with doing the same thing on the working board. I put this off because I couldn't locate a suitable bulb or pair of bulbs.

The advice from Nophead was simply to connect 12V power to the regulator and check that 5V came out.
Referring to this website, the power supplied to a 7805 regulator need only be 7V or more; a-ha, say a 9V battery, then, since I didn't want to connect the whole circuit again.
I roped in assistance, and connected wires to a PP3 battery with the ol' trusty Blu-Tack and held the +ve end against the reglator pin next to the "rrrf" text on the board, with the -ve end against the flat plate of the regulator, whilst my assistant measured the voltage off the pin next to the "make" text against the ground pin on the Molex-style connector. Oh. No voltage output. That would be the problem, then. No wonder the power LED didn't light, as it wasn't getting any power at all, it was all just going straight to ground!
That means the rest of the circuit hasn't been tested under voltage since the chip blew!

So for my next order, a new 7805DT voltage regulator..... And I said I might need the chip-leg cutter again, looks like it was sooner than I expected/hoped!

Nophead also explained that I could check the 0.25 ohm resistors by reading the resistance on the meter with the probes touched together, and subtracting that reading from the one I get on the low-value resistor. I'm going to try that next.

In the last 3 days, I have learnt a huge amount about checking boards.
I shall update the project costs soon.
.

Monday, 21 September 2009

Yes!

I made up the 3 ribbon cables today for the 3 stepper motor driver boards. As I did so, it occurred to me that the cables connected these boards to the motherboard, and that as the cables had the same connectors on either end, the motherboard must have an IDC header, which is the part I ordered singly, instead of a set of 3.
Sooooooooo, I nicked the header from the motherboard kit in order to make up the second board.

On positioning the parts for the second stepper motor driver board, I was careful to orient the chip correctly!

When I cooked the second board, I did so withOUT the large electrolytic capacitors in place.
I cooked on medium to heat the board up and then as soon as the solder paste started to melt I turned it up to medium high. All told, it took just over 3 minutes. Nothing moved at all. There was distinctly more smell this time - last time was almost smell-free.

On cooling, I checked all the contacts from the chip (which was perfect, with no bridges at all) along the traces as drawn on the board. I removed the solder balls with the back of the knife blade again, and checked the resistance across all of the solder mount resistors from solder to solder. All was well. I had just one capacitor that had made good electrical connection but was not good mechanically, having far too little solder. I put the tiniest bit of paste on that end and used the soldering iron with chisel tip to make it good. I also used paste to solder the electrolytic capacitors in place, carefully positioning C11 as far away from the end of the chip as possible whilst leaving exposed solder at the other end of the capacitor to facilitate soldering.

I then ordered 2 more headers for the next board and the motherboard, and a replacement driver chip from Farnell.

I soldered in the stand-in giant resistors, and the through-hole components (with the nicked IDC header), and inspected and tested everything (that I could follow and understand).

JOY! This time, no drama, and the power LED lit up. Yes!
Now I have to wait for my next Farnell delivery before I can do the third board.

Verdict: death by misadventure

"He died instantly, they say. No pain. He didn't stand a chance, the poor chip."






It seems the first stepper motor driver board's chip didn't stand a chance (and there may have been nothing wrong with the soldering after all). On inspecting the first board for damage, I noticed the semicircle drawing at one end of the chip's print on the board, and realised this was probably supposed to align with the dimple at one end of the chip. Unfortunately, being a complete electronics novice, and being unaware of the marking/importance, I had the chip the other way around. There had been nothing in the instructions to be careful about the chip's orientation. Guess we are supposed to know that. Well, I do now! (Funny how everything else was specified, though.)

I live and learn.


Sunday, 20 September 2009

Rice Krispies

Apparently, Churchill said, "Success is going from failure to failure without a loss of enthusiasm".
I must be heading for success then!

Firstly, I must thank Nophead for sending me those spare parts - I have practice material! More later.

The instructions for the stepper motor driver board say to plug it in to see if it works, but I didn't have a 12V power supply. Maplin, as usual, didn't have what I wanted, so I ordered from Farnell again and ordered spare surface-mount LEDS, too. I was underwhelmed to find the power supply didn't come with a lead! I dug around in the long-since-abandoned-shelving upstairs, and found the power lead for either my old PC or its CRT monitor. It had a 5 A fuse, so that seemed OK. Plugged it into the power supply - and nothing. Checked all the switches were on and the socket was live, all OK. But no power from the PSU. Wondered about that old lead? Then I remembered somebody telling me something about how ATX power supplies differed from AT power supplies, so some internet hunting later, and I found out how to short out pins in the power header for testing purposes.
Usually the power header is a 20 pin affair, but mine looks bigger. It has a separate 4 pin block slid* onto the end of the larger connector.

Here is a picture, with the power header shorted between pins14 and 17:



Thank goodness for the internet and the wealth of information available on various websites.

This done, I switched back on - and it was a good job I was watching the fan closely, because I watched it disappear as it spun at speed, but I couldn't hear a thing. Wow, I know it is called a "silent" PSU, but I didn't expect that they meant it!

Barney reported a blown chip, with the advice to check continuity on the board before plugging in. My meter has dead batteries....

Now I had a working PSU, I switched off, plugged one of the Molex-type leads into the board until it
snapped into place and switched on with my finger over the off switch. Here was the crackle and pop. I switched off very quickly with a slight burning smell developing. What was that, you said, Barney? Something about checking continuity everywhere?

Ooops, I have given the chip a contour! but it doesn't look like the board is damaged.

This time following Barney's advice (!) I shall nip the legs with the tin-snips if I can to remove the dead chip. And I'm going to Screwfix now for some replacement meter batteries - open on a Sunday and ~£2 cheaper in total than Halfords.
Then I shall inspect the rest of the board, and CHECK CONTINUITY everywhere. Without the chip in place, I should get better access. Then, if all is well, I shall replace the chip and check the continuity from its legs, too.

Soldering/desoldering learning.
Following on from a link off the forum for Kapton tape supplied by DealExtreme in the States, and looking to see what else they had, I noted that they had desolder braid with lots of reviews, including one that said this particular desolder braid had flux in it, so you don't need to add any. Ah-ha, maybe that's why my desolder braid isn't very successful for me, as perhaps it doesn't contain flux, and I wasn't adding any.
Order from CPC (another part of the Farnell empire) a flux pen. Also a conductive pen as a temporary fix in case I blow any of my board tracks.
I shall try the fluxing/desolder braid to remove the remnants of the old chip legs. If I'm not getting anywhere I shall leave them in place rather than risk damaging the board. Then I'll clean the area with surgical spirit, in case there is contamination after the smokey smell.

Also, I have seen a video of soldering 1206 parts by hand with solder wire, and this requires flux to be put down first and touched with the soldering iron to "tack" the part in place, before laying solder wire partly along the end contact of a component, and just bringing the soldering iron (using a chisel tip, with the flat face downwards) down onto the edge of the pad, sliding it in to touch the part and sliding straight back away. This gives minimum iron-exposure to the 1206 component. I'm going to practise this technique when I have my flux pen. I suspect my 0.7 mm solder wire may be too thick, though; it needs more like 0.4 mm.

I have already practised using the chisel tip and soldering a 1206 component using the solder paste, which itself tacks the part down. This was pretty successful, too. Knowing I can use the soldering iron with the solder paste, when I replace my chip, I'm going to use the solder paste in a thin line across all the pads.

Farnell sub-total = £19.64 (agh, I forgot to order the headers!)
  • 350 W PSU, part number 1277264, £15.68
  • green LEDs, 1206, part number 122672, £0.061 each (x10)
  • red LEDs, 1206, part number 1318261, £0.079 each (x10)
No delivery charge, but total VAT of £2.56.

CPC sub-total = £25.14
  • no-clean flux pen, part number SA00859, £5.79
  • conductive pen, micro-tip, part number SA00462, £19.35
No delivery charge.

ScrewFix sub-total = £3.82
  • LR44 cells, pack of 2, part number 44122, £1.91 (x2)

Running total (excluding set of washers and screws from B&Q) = £432.63

So I STILL need 2 headers and another A3982 chip.

* On a complete and utter off-topic aside, I was thinking about how the past participle of the verb "to slide" is slid. That's (about?) the only one. For glide it is glided, pride it is prided, side it is sided, and for ride it is ridden.
Isn't English a wonderful and contrary language?!

Tuesday, 15 September 2009

Step(per) 1 finished!

I finished the first stepper motor driver board today. My second mega-resistor went better than the first. I am amazed how often I end up needing to use Blu-Tack to hold things in place; it should be named on the parts list under tools!

So here is the front of the board:


and here is the back, with its near-perfect soldering:


I just wish I could test it, but I don't yet have a 12V power supply, nor do I think I can mock one up, as I did for the 5V previously.

I am very grateful to Nophead who has promised me a replacement 100 nF ceramic capacitor and surface-mount green LED, so I should be able to do the reflow work on the other 2 of these boards towards the end of this week.

I'm hoping to read Barney's blogging of his reflow experiences before I do more, to see if I can pick up any tips.
I really appreciate the help and encouragement and practical assistance given freely on the forum and in people's blogs and comments. It's something special.
I have learnt that these boards that have been giving me quite a challenge are now available ready-assembled! Oh no, they're not are they? I could have waited for that had I known it was in the offing.
Oh well, at least at the end, I can say "I made all of that", with some pride (especially if I have a working 3D printer!) because I knew how to do NONE of this 6 months ago! And I couldn't have done it without the RepRap "community" being what it is.
Meanwhile, I can tackle the cabling, or I've still to try out those penny washers on my mechanical build.

Monday, 14 September 2009

So far so good

I was soldering the remaining components on the dreaded stepper motor driver board last night.
I started with the small components, my fine soldering iron tip and solder wire. Having clipped one of the RJ45 sockets into the board, I discovered that it was impossible to get the other one in due to the ridges on the sides of the components. I carefully unclipped the first, and filed off the ridges on the sides of both RJ45 sockets that will be next to each other on the board.

I did some excellent soldering of the small-leaded components, and I was so impressed I took a photo'....
This is only the fifth time I've soldered. Can I just say woo-hoo!!!! Yeah!

I found that if the solder wire wouldn't melt after more than 4 seconds, cleaning the soldering iron and/or re-tinning and cleaning it improved the heat conduction. I also noted that just 4 dabs of the 0.7 mm solder wire per lead was perfect for these fine leads.

For the break-off 4 way header, I "Blu-Tak"ed the front onto the edge of the board to make a firm fit ready for soldering. I was glad I'd re-mounted the edge electrolytic capacitor because I wouldn't have been able to fit the Molex-style connector otherwise.
For this and the other large-lead components, I swapped to a larger soldering iron tip.
I used 8 dabs of solder wire for each of these larger leads but on inspection I found this left the solder only level with the board rather than beaded, so I went round and did the same again to get a bead! You really need thicker solder wire for such components.

Here is the finished through-hole soldering. You can see the Blu-Tak still attached on the left of the picture.


For the first mega-resistor, I tinned the leads, which had been bent round very carefully to align with the pads without touching any neighbouring components, nor to have the resistor body touching anything. I also tinned the pads, and then used the soldering iron at an angle that prevented contact with the chip/neighbouring capacitors etc to melt it all together using a little more solder to get a firm footing.
This was extremely awkward and took me a long time. I stopped after the first one, so I still have the other to go. I am not looking forward to having to do this on the other 2 boards. Don't buy these resistors!

It was too late to blog afterwards, but I'm afraid that's when I took the photo's, so they're not so good - but my soldering was fantastic!

.

Saturday, 12 September 2009

And one was where 3 should be...

I have set out the remaining components for the first stepper motor driver board. You can see the re-positioned edge electrolytic capacitor.


The two enormous (in comparison) black components on the right are the stand-in resistors, with their leads bent to fit the board's contact pads!
The component in the middle of these two is the high power header connector - you may remember that's the part I ordered in numbers way over the top, because actually you only needed one, which is broken into 4-way parts. The first go caused a 5-way part (!), so after that I tried needle-nose pliers (too wide), and then cutting the plastic with tin-snips. This worked a treat, but I was glad I was wearing eye protection because each cut part fired off, and bounced off 2 or 3 obstacles before disappearing! I would see where it went first and second and then lose it! Took me a while to find it, based on the landing noise it had made!

See the blue header at the bottom? That's the only one I have. Remember there are 3 stepper motors, and therefore 3 driver boards? Somehow I failed to order 3 of these headers!

So for future orders, so far, the list goes:
  • 2 more headers, part 110-3949 from Farnell
  • 1 more ceramic capacitor, 100 nF, part 165-0887 from Farnell
  • and 1 green 1206 2 mm LED, which I might get from Farnell as well, say part number 1226372 at 6p.
I'm not ordering yet - let's see how many other parts need replacing.
So it will be a while before I finish these three stepper motor driver boards.

Fix part 2

I cleaned off what I could of the solder on the removed electrolytic capacitor, and manually soldered it back on to the board, using Blu-Tak to steady the side as I did so.
I de-soldered the dud LED, and checked it afterwards - it really is dud. I checked a new one, which lit, and soldered it into place, again using a tiny bit of Blu-Tak against its side. Now it doesn't light. Hmmm - methinks my logic is off, possibly because of the rest of the circuit. I just can't believe this LED is as dead as the other after simply soldering it on. Unfortunately I don't have a 12V supply with which I can check this part of the board, which is the power circuit.

Checking

Since I couldn't see one of the pads under the edge electrolytic capacitor (C10), I wasn't able to check continuity across the pads to see if the capacitor had made decent contact with the board. I tried checking from the wide terminal of IC3 5V regulator to one side of the capacitor (continuity found with R set to 2000 k ohm on multimeter), but could get nothing from IC3 to the other side of the capacitor.
I decided to see how firmly it was attached, and when it wobbled slightly under pressure, I peeled it away from the board. I shall remove the solder that's there and re-solder by hand.

As for the other electrolytic capacitor (C11), I can't get any readings at all, owing to the proximity of the chip on one side and the molten black plastic in the way on the other.

I checked the LEDs with the diode setting on the multimeter, and was pleased that all A B C and D LEDs lit up, and that using the probe terminals the wrong way round lit up the neighbouring LED instead! That shows that there is continuity of those circuit portions.

Unfortunately, I couldn't get the power LED to light at all, even using the component casing (either way round), so I guess that's a dud, then. That means I can't check the power circuit, with those electrolytic capacitors, as a whole. More hand-soldering coming up, but again, I don't have any spares.

Getting a quick fix

OK, that wasn't too bad. After perusing various websites to learn how best to deal with my little cooking problems from last night, I set up my soldering iron with its finest tip, and had my solder wire and desoldering braid (and tweezers this time, after discovering I was burning my hand last time I used the braid) to hand. My iron tip is actually finer at the very end than the tweezers.


I started off trying to use the braid to deal with those solder bridges on the chip, but just couldn't get the braid hot enough to melt and draw out the solder in the gaps between the legs. After trying several times, I simply used the iron tip to heat the bridging solder directly, then quickly drew the tip down, bringing the solder with it. This spread the solder onto the legs either side, and I did this for all the bridged legs until I soon had no more bridging.

Here is a picture of the legs on one side of the chip:



and here is the other side:

OK, it's not exactly pretty, but it should work.

Next I used the iron to melt the solder at one end of the cracked capacitor, and used tweezers at the same time to encourage separation. I only moved it a bit whilst the solder was molten. I repeated this at the other end, and went back and forth a couple of times until the capacitor was freed.
While there was free access, I used my Stanley knife blade on its non-blade edge to remove the problematic solder balls, and cleared the others off the board, too.

I put a new capacitor in place, and using my fine soldering iron tip, still, with 0.7 mm solder wire, I was able to solder it in place, although positioning it whilst soldering was awkward. I used a tiny blob of Blu-Tak on the end of the tweezers to try to stop it sliding around. You can see it here (it is capacitor C1 just in front of the chip) and isn't straight, but it has made contact. There is too much solder there, too. Tough!

I used the soldering iron to try to melt the solder under the centre electrolytic capacitor, trying hard not to put too much heat onto the neighbouring (and very close) chip, but mostly melted the black plastic base of the capacitor, so I can't see if the solder has melted!

So here is the fixed? board:


Only, I think there is another problem - the electrolytic capacitor on the edge. The capacitor isn't aligned with its board-diagram. There is contact on one side:


but on the other the lead on the capacitor is visible, but the pad isn't, and I don't know if contact has been made. You can just see the lead obscuring the C6 marking:

Now how do I check the electrolytic capacitors for contact?

Friday, 11 September 2009

....Cook!

Into the cold frying pan, onto the gas hob turned to medium low. I timed it, too. At 2 mins I could see the first two corner parts (motor LED and resistor R7) going melty, but it was nearly all melty by the time I'd taken the photograph:

It is hard to take photographs above a hot frying pan, so once again, apologies for the blurs!
And you really can hear some little "pop"s.

At about 8 minutes everything was melty, to varying degrees, and those first 2 parts were shiny, so I shifted the board around to even out the heat-load better. You can see them at the top of this picture:



The shiny isn't silver as the solder wire goes, but is gold-coloured.

By 10 minutes, the only parts not shiny were the chip and its neighbouring electrolytic capacitor. I moved the board to centre these over the heatsource, and waited some more.

I was concerned that the chip wasn't properly down, so I...

don't try this.....

tried to press it down with my tweezers..... and nudged it out of place.... at just the wrong time....

:-(

Ooops. Quickly shoving it back where it should be, I waited another 2 mins, and its solder paste did go shiny. One side is well-aligned and the other? Not so great. It's on the pads, but not perfectly.



And I caused a lot of bridging where the solder isn't separated between the legs. I thought it all looked done, so I turned off the gas, and inspected the board from above.

On cooling, I took some more pictures, showing the poor chip legs (the 5 left-most legs are bridged and two to the right are bridged), and solder balls in various places. You can see one here in front of C6, in front of the rear electrolytic capacitor:


As warned in the assembly instructions, I have the centre electrolytic capacitor (on the left in the picture below) not at all shiny, and needing some post-cooking fine-tipped soldering iron attention.


Once cool (about 10 mins), I went around the board and chipped off the solder balls with the tweezers and.....

.....don't do this either.....

where there were 2 between C1 and C4, I think I managed to crack one of the ceramic capacitors. Oh Blogger!!

¦-[

Next time, I need to leave individual components well alone whilst cooking, and have a finer implement on hand for removing solder balls. Perhaps my Stanley knife blade, used on the non-blade side, may be better at removing problems
between components if I carefully draw it through the gap.

Oh dear, that wasn't very successful all in all. Will I have to replace the cracked capacitor at C1? It is a 100 nF one, and I don't have any spares.
I have to use the soldering iron to fix the electrolytic capacitor, somehow fix the solder bridges on the chip legs, solder in the resistors that are standing in (literally) for the ones I couldn't find as surface-mount, solder the other through-hole components, and I still have a solder ball between C1 and C4.....
.

Ready, steady,.....

I took the solder paste out of the fridge some hours ago. I had to use pliers to unscrew the clear sealing cap, and to screw on the blue plastic nozzle. Looking at it, I can see patches of yellow in the paste (flux?) as if it isn't properly mixed. You can see it in the picture below under the word "Omni".

The part near the nozzle looks homogenous, though, so I'm not too worried. I probably won't get to the separated paste further down the syringe.

I began to coat the surface-mounting pads on the stepper driver board, carefully doing the pads in the order as given for placing the components so that I wouldn't end up coating the pads for my non-surface-mounted 0.25 ohm resistors. Here is an action shot of paste just about to be applied to the motor pads.


Here is the pasted board - you can see R3 and R16 (below and above the chip location, respectively) left untouched.


Reading those instructions on LED orientation didn't help, because my LEDs have a green "T" marking on the underside, so it wasn't obvious which end is which. I guess if I get it wrong the LED simply won't light!
I went back to RapidOnline, who supplied the LEDs, and looked at the full tech.spec. as given for the part number. The data sheet shows current flow to be in the direction of the "T" from top to stem, so I've aligned the triangle on the LED's data sheet diagram with that on the circuit diagram for the board.

Here is the pasted/assembled board, all ready for frying (except it's tea-time, the cooker is in use, and I'll have to wait!):


I was surprised to find that the board was more robust in this state than I expected, and had no problems moving it to take the photograph.

On the surface

It has taken me about an hour to get together all the surface-mount parts for the first stepper motor driver board, and I haven't even put them (nor even the solder paste) onto the board yet. I'm very glad I used my own identifiers when I submitted my order to Farnell, because one rating of ceramic capacitor has no useful information other than "capacitor" on the Farnell label, so I was glad of being able to cross-reference. Also, having a spreadsheet of suppliers for each component per board was useful, so that I knew I was looking for a RS part for this and a RapidOnline part for that, for example.

Here is a picture of different packaging, of resistors: same idea but this time mostly soft card with transparent film windows in it.

Here are all the surface-mount parts laid out around the board. You can see one capacitor still in its packaging towards the bottom of the picture - that is to distinguish it from the others.


I had forgotten that I hadn't been able to find everything as surface mount, and now I look at the 0.25 ohm resistor, and go, "Oh my, how on earth am I going to mount this on the surface? It's (relatively) huge".
Now I do remember BodgeIt giving a link to his non-surface-mounted component done as surface-mounted, so I'm hunting that down. I shall have to stand this resistor vertically because it won't fit in any other way. So I'll do that when I do the manual soldering for the through-hole components.

Seeing more clearly

I had bought a set of magnifying glasses to help with the assembly/checking of the circuit boards. It suddenly occurred to me yesterday evening that I could perhaps try taking the photographs with the magnifying glass, since my camera really doesn't like very close-up work, despite having a close-up setting.

Tried it out this morning. Holding both items steady with the magnifying glass against the zoomed out camera lens, and trying to avoid casting one huge shadow over the subject was tricky, and I had to use Blu-Tak to hold the subject, but I am quite pleased with the results. I shall use this technique in future.
So here is the stepper motor driver board, again,



and then the strip of capacitors showing the opened end if you look really carefully (it is the invisiblest film - do you like the new word?), and then the front of the capacitors' packaging.


You can see the scale of this against the camera strap on the right of the photo'!

Thursday, 10 September 2009

First stepper

I started assembling the components for the first of my stepper motor driver boards today. The one shown on the instructions on the reprap site is red, but mine are all green. The printing on mine is much less clear, too, so I have the website page saved as a file on my laptop, and I am scrutinising the pictures and text on screen rather closely.
Also, none of my boards have been printed or perhaps cut square, so the fixing holes in the corners don't line up.
I shall have to mark each fixing hole individually to mount the boards on Faith.



This is the first board on which I shall be soldering surface mount components. I began with the 0.22 uF ceramic capacitor (as it says in the text), also known as the 220 nF capacitor as it is marked on the board. Apparently. I can't make it out on my own board!

For those of you new to surface mount, this little capacitor (which I am assured is large - ha!) comes in a little strip of packaging. I tried to take a photograph, but the packaging is clear, and the components tiny, and the camera couldn't find it to focus!
You have to peel back the clear plastic film from the back of the packaging to get at the capacitor. And then it jumps right out...
it is a fawn-coloured thing, tiny as I said before (!) and I am wearing grey trousers. It jumped towards me. I had to search for it; I could barely spot it on my lap!


The instructions say to colour it with a red or black pen, to distinguish it from the other similar but differently rated capacitors, but as I had only a green marker pen, mine is green. Colouring it wasn't easy, either!

Here it is. You can just about see it in the photo' (the camera clearly couldn't, or couldn't clearly!)


Oh this is going to be fun, isn't it?!

On a lighter note, I've got my soldering tutorial up on the Builders' Wiki, with a lot of practical technical help from Renoir, and my purple RJ45 cable arrived.
.

Monday, 7 September 2009

Camera shenanigans, RJ45s and penny washers

An aside, really. I have discovered something about my Fuji FinePix camera; when the batteries are getting low (which happens ridiculously quickly), the autofocus doesn't always - it takes about 6 goes to get it to activate even when it is set to come on. That explains a lot of my blurry photographs. Also, I accidentally found a setting to increase the brightness, which makes it much easier to see on the LCD screen whether or not I have a decent photo'.

eBay delight! After yet more advice from the forum folk, I ordered some straight (not crossover) patch (ie not solid cable) RJ45 cables. I have guessed that I will need about 1m lengths for Faith.
Now I could have got these at 99p each, but that would have been boring grey, so I ordered 1 red, 1 yellow and 1 green for £1.25 each from Conquest-Computers, and 1 purple for £1.49 from Bluecharge Direct, all inclusive of P&P.
Because these eBay items are listed separately, the Conquest Computers' order went through as 3 separate transactions. Handily, they worked this out and shipped them all together in a Jiffy-style bag. I am still awaiting the purple one from the other company.
I have also ordered some penny washers from eBay, size M5 with outer diameter 25 mm. I am hoping these will be the right size for the swivel arms of the x/y/z stages.

eBay sub-total = £8.89

  • RJ45 cables from Conquest Computers, £1.25 each, x3 inc. P&P
  • RJ45 cable from Bluecharge Direct, £1.49 inc. P&P
  • M5 x 25 mm penny washers from Astley Components, £3.65 inc. P&P
So recounting costs,
running total (excluding last set of washers and screws from B&Q) = £384.66

The noise suppressor board

I forgot to mention the problem I had setting up my new soldering iron stand. I had to use the fluted coil (holder) upside down, because my Maplin soldering iron has a couple of screws by the tip, making it too wide to fit in the normal way up. This necessitated using pliers to force the coil apart at the (now) bottom end in order to twist it out, and to shove it over the plastic support!

Today, I set to, soldering the noise suppressor board, and as before got part way through when I had to pause to ask a question of the forum folk; the screw terminals component had leads but also made contact with two other pads, and I wasn't sure if they were to be soldered as well. The advice came that I could ignore them, so I soldered just the leads.
When it came to soldering on the tiny tiny tabs into huge holes on the board, I was at a bit of a loss. I secured the motor against the back of the board using an elastic band (left by the postie). You can see the capacitors' outer legs left un-trimmed, for soldering to the motor casing later on.


The instructions warn you to use a lot of solder, but it was difficult to heat the large round contact and each tiny motor tab (taking care not to damage it) as they didn't fit snugly together. Eventually I had a mass of solder there, but not exactly shiny, no matter what I did.
Soldering the legs of the two outside capacitors onto the motor casing proved to be even harder. I tried cleaning the casing first, and tried to tin the casing before affixing the leads, but neither joint looks pretty, and in fact I had to re-do the second one three times. Then I affixed the cable tie to hold it together firmly, and this second joint clearly moved!
I ended up using the desoldering braid to remove the solder. That wasn't easy, either - I wasn't expecting the braid to get hot, and I found my hand getting uncomfortably hot holding it. Also, it didn't seem to wick, but I did get a blob off at a time. I wonder if that's because of using the higher temperature, unleaded solder?
I tinned the capacitor lead, and squashing the end of the lead down onto the motor with the soldering iron held parallel and on the topp of the lead (and obscuring the lead from view) and moving the iron along and off the tip of the lead as soon as the solder melted.
This fourth time made contact.

Not exactly tidy, though!
Still, I set the multimeter to the lowest resistance setting and used it to check from the left screw terminal to the left tab on the motor, and from the right terminal to the right tab on the motor, and both gave 0.05 ohm, so I believe I have continuity despite the problems encountered.

I guess next it will be my first try at reflow soldering....

Soldering - a "how to"

Here is what I gleaned from extensive reading before I started to solder. I put together everything pertinent that I learnt, in my own words, and went over it afresh before starting on the opto endstop boards. You could call it a tutorial. Unfortunately, it isn't possible to grow a third hand for taking photographs whilst actually soldering, and my photo's aren't perfect anyhow, but they give an idea....

How to....

Check that you have all the right components for the board. It is a good idea to lay them out around the board, each on the respective head/foot/left/right side, to assess sizes and locations of the individual components.

Start with the smallest component on the board.

Firstly, check the component leads for signs of dirt or corrosion (see later), and clean by wiping as necessary. If the component has been shipped stuck onto tape, cut the leads alongside the sticky tape to prevent future issues with glue interfering with the solder joint.


Bend the component leads down to align with the fitting holes in the board. Check which way round the component must be inserted; with some components this doesn't matter, but with others it is critical. Insert the leads, from the top towards the bottom surface of the board, both at the same time, but do not press the component down onto the board, because that may kink and weaken or snap the leads.

For any component that may heat up in use, eg a resistor, leave a small gap so that the component is raised above the board slightly to allow air to circulate and heat to dissipate. For temperature-sensitive components, eg transistors and diodes, where excessive heat from the soldering operation can be harmful, again leave a small gap, so that a small crocodile clip or similar metal item can be attached - during soldering - to act as a heat sink and dissipate excess heat.

Bend the leads outwards away from each other slightly on the underside of the board to hold the component in place.
(This picture shows a ferrite bead sat vertically on the board, but most components will be aligned between their fixing holes, known as pads.)

Cut off the leads a few mm (approx 3 mm) away from the board. Do not cut them off flush with the board. Cutting the leads before soldering prevents disturbing or damaging the finished joint.

Repeat with one or two other small components, working from the centre of a big board outwards.

Now heat up the soldering iron. Clean the tip using a dampened card egg-box (my resourceful Dad's method) or a wetted sponge (commercial method). The tip should be shiny.

Apply the tiniest amount of solder, containing flux, to the iron tip, by just touching the solder against the tip, but all around it, to prevent it oxidising. Now wipe the tip on the damp card/sponge.

If the component leads are lightly corroded, and not shiny themselves, use the soldering iron to heat the leads. Without moving the soldering iron, now touch the solder to the lead on the side away from the soldering iron.
Move the solder wire away, remove the soldering iron and check that there is now a layer of solder around the lead. This process is "tinning". "Tinned" parts will solder together well. Discard the excess solder blob on the iron tip by wiping it on the dampened card/sponge. If too much solder is applied to the part being tinned, use desoldering wick/braid to remove the excess by applying the wick to the coating, and the tip of the soldering iron to the wick, gently pulling the wick along under the iron tip as the wick becomes full of solder. Remove both wick and solder together.

On the underside of the board, use the hot iron tip to heat the lead AND the copper connection together, for just a second or two. Now, without moving the iron tip away, add a tiny amount of solder to the side of the lead by touching the solder against the hot lead and copper connection, followed by quickly adding solder, using a dabbing motion, to the side of the lead away from the iron, again down against the copper connection.
Repeat this movement until sufficient solder has been applied to create a good joint. Take the solder wire away, then immediately remove the soldering iron, to avoid boiling off the flux and creating spikes, without knocking the joint. Do not move the board until the solder joint has set.

Now inspect the joint.
The outline of the leads should be jutting out of the solder joint slightly. As the joint cools, it should have concave sides, should be flush against the copper connection, and pulled up around the component lead. The solder should not "bridge" to neighbouring connections. If using leaded solder, the joint should look very shiny; lead-free solder will look a little duller or grainier, but still shiny.
Check the joint from the top side of the board, too; the appearance here should be the same.

If the solder does not look shiny, or has not flowed around the lead well, re-melt it with the soldering iron slightly hotter, and ALWAYS add a small amount of flux, which may be contained in extra fresh solder, as necessary, so that the joint becomes shiny and complete.

Below is a picture of a row of good joints in the foreground, - this was my fourth board ever, so it isn't perfect,
but the front left solder-joint is perfect, in size, shape and shininess. The brown marks you can see on some of the others are burnt flux, which can be cleaned off with a commercial cleaner or by scraping gently (eg fingernail), but in this case don't compromise the electrical contact.

Here is a close-up picture of the joint on the left in the background; this isn't good, having too much solder. You can see that the solder is convex instead of concave. However, it has made electrical contact and is a viable join.

Here is a picture showing a bad joint; there are 2 large connecting holes in the middle of the board, and you can see that the top one in the picture has shiny solder in it, whereas the bottom one has dull solder. This would be a bad joint if it all looked like this. In this case, the solder on the other side of the board is shiny and I believe there is a sound connection there. Otherwise this would be a candidate for re-doing the solder joint.


Continue with the other joints, checking each as it is completed, before moving on to the next. Re-clean the soldering iron tip as necessary, probably after every few joins.

When the first batch is soldered successfully, continue with another batch of components, moving up in size and outwards on the board.
Finally, add a tiny amount of fresh solder to the tip, to protect it from oxidation in storage, before switching off. Store the soldering iron covered to keep it clean.

.

Friday, 4 September 2009

Testing 1, 2, 3, testing...

Before I went any further, I wanted to test the opto circuits I'd built, so I needed to know which pins were which on the RJ45 connector. I used this, which was the clearest description I found, with a nice easy diagram - so looking at the RJ45 jack socket on the board, with the board the right way up, the pin on the left is 1.
According to the circuit info. in the assembly instructions, pins 4 and 5 are connected together, and this is where the +ve end of my 5V power supply had to be connected, and pins 7 and 8 are connected together, GRND, and this is where the -ve end had to be connected.

Below is a photograph of my testing set-up, using 3 D cells (giving approx. 4.5V) and some alarm wire all blu-tacked together. It took some fiddling to get continuity; too much blu-tak insulated the alarm wire strands!



I stood the battery-tower up and wedged it inside a perfectly-sized cardboard box to hold it all together better. Here is a photo' of the circuit board with its optical sensor blocked with some folded corrugated card (the wire in the foreground is not actually making contact yet) , and below that a photo' with the LED lit.




Believe me, holding the wires to get this working whilst taking a clear photo' was no mean feat!
Hoorah! All 3 circuits work as hoped, with the LED lighting when the sensor is blocked, and going off when unblocked. I am delighted! My first ever soldering was a success!

Tuesday, 1 September 2009

Silkscreen and solder

Some photographs:

here are all the packages required for the opto endstop board laid out
,

and here are the individual components placed around the bare board,

and here are the undersides of the three finished items


I know the photo' is poor, what with being blurred and having terrible reflection off the auto-flash, but you can just about see the scorch mark at the resistor on the first one I did (on the left), before I swapped to a finer tip on the soldering iron.

Now I need to determine which connectors are what on the "ethernet" socket and get myself a 5V power source to check all the opto endstop boards.

Here is a better photo' (new batteries in the camera, daylight (of sorts)) showing the first board:

The slight scorch-mark is (on the middle resistor) just above and to the right of the central fixing hole.
.