Board PCB discussion

[Tony]

Suggestions for improvements, mistakes, hints here please.

[SpankyMcSpank]

Looking good, easy to follow instructions...

I assume that the underboard 14v zener diode is facing the same direction as the onboard one (maybe a pic of the underside in that location for orientation purposes.

And is there clearance for a low profile IC socket for the PIC?

[Tony]

Looking good, easy to follow instructions...

I assume that the underboard 14v zener diode is facing the same direction as the onboard one (maybe a pic of the underside in that location for orientation purposes.

And is there clearance for a low profile IC socket for the PIC?

It's exactly the same, I'll add a picture to make it clearer though.

The above board clearance is 6mm and below 2mm so not much room for a socket. You could drill the holes out and try using short 'flush fitting' socket pins.

[sean4star]

I've hit my first snag. I've got one row of the board assembled (it's the row closest to the power connections). I started adding board coils at the far right of this row (if the power connections are closest to you). I have 2 completed display pieces, so I was testing each coil as I added it and then compared it to the other coils. I got the 3 coils on the right connected and everything tested fine. Then I added the fourth, this is the coil just to the right of the center of the board. It tested fine so I started moving the 2 displays between the 4 coils to see if the brightness was consistent. I ended by putting the two displays on the 2 coils on the far right (the first two that I connected and tested many times without problems) and that's when one of the resistors started to glow and smoke. I've circled it in the attached pic. Any thoughts on what would cause this? I've looked for shorts and everything seems to be in order. I did make the correction for the "New PCB track error" that Tony recently posted. I haven't replaced the resistor yet, hoping someone might have some thoughts or suggestions for what I should test and/or fix?

[Tony]

I'd guess one of the 2 mosfets on the left will probably have shorted. If not is it possible a bit of stray solder/wire could have caused a short while working on it?. That resistor protects the supply to the 2 coils on the left of the photo, a short from either coil terminal to ground or a faulty mosfet wil fry it.

[sean4star]

I don't see any shorts. Everything looks just as it should. I suppose it's possible a stray bit of wire was on the table, but I guess I will never know since everything is all cleaned up know.

I replaced the resistor, but now none of the coils seem to be providing power. I can't get any of my displays to light on any of the four coils. All 3 of the diodes by the PIC are showing the correct voltage across them, the one with 5V and the other two with 2.5V. Any advice on how I can troubleshoot where the problem is?

[Tony]

Check the voltage at either end of the 6R8 resistors, the 2R2 fusible may have been damaged as well. Check the voltages at each coil terminal and post the readings. You seem to have long 'tails' of wire left on the coils, it's possible one of those shorted for a second and caused the problem.

[sean4star]

I moved the coils and what I found was pretty interesting. So, all four coils were in the first row on the right. I tried moving them to the second row, but the displays didn't light up there either. Then, I moved them to the left side of the board in both the first and second row. The left side of the board works just fine. So whatever the problem is, it is only affecting the right side of the board.

I checked the voltage at the 6R8 . I checked the 6R8 on the right side of the board (the side that isn't working) compared to the left side. The right side slowly ramps up the voltage. It took probably 30 sec or more to get up to 8V. The left side was instantly 12V. The other thing I noticed was that the right side would slowly ramp down after the power was disconnected, while the left side dropped down close to 0 immediately.

Same thing with the coil terminals. The left side of the board had 12V at all the coil terminals. On the right side it maxed out at 9.5V, that's after waiting for a little while.

The 2R2 is interesting. The one on the left is 12V on both sides. The 2R2 on the right (the bad side) is 12V on the side closest to the center of the board and only 9.5V on the other side (again, taking a while to ramp up to the 9.5). Would that tell you that the 2R2 is damaged?

I hope this helps with the diagnosis...


And I bet you are right about the "tails". I left them on because I wasn't sure if I liked the way I had the coils hooked up to the terminals, and if I cut the tails then the wires would be too short to reattach if I tried to change. I've settled on a way that I like so the tails are gone.

[Tony]

Yes it's the 2R2, it's deceptive as it's not totally o/c and is allowing enough power through for the PIC to operate but not the coils.

[sean4star]

Excellent! Everything is replaced and all is working again. Thanks for the help.