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!)

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.

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!