Promethium Problem

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HamishR

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I just started build a Promethium today and have so far only populated the board with the resistors, the diodes and the IC sockets. I am about to install the 1µF caps C10 and C12 and the only caps of that value I have which will fit are tantalums. The board has no indication of polarity for these - what sort of 1µF caps am I supposed to use? There isn't the room for poly or electrolytic.

So I got my meter out to work out to check which ends to connect where according to the schematic only to discover I have no continuity between the IC's pin 7 and the pads for C10. I get continuity between pin 7 and D2 and if I look at the underside of the board I can see the PCB trace goes to the left-hand end of C10 and C9 but my meter gives me no signal at those points. The board looks fine and there's no way I burnt a trace or anything.

Then as I look on the back of the board at where R18 is soldered to the board I can see a tiny bit of copper poking through the black coating. prom02.jpeg

It's the fourth solder joint down on the left. Is that a piece of trace poking through?
 
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That's exactly my point - there should be continuity but there isn't. I checked from that sliver of copper to the upper right red circle (end of 220K which goes to pin 7) and there is continuity - but not between the copper and where you have put the lower left circle. What has caused this? I haven't overheated that join, haven't ripped through it with a chainsaw - why has the trace done that? Can I trust the rest of this PCB?

I can easily bridge those points and that was my plan - but what has caused this?
 
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HamishR said:
That's exactly my point - there should be continuity but there isn't. I checked from that sliver of copper to the upper right red circle (end of 220K which goes to pin 7) and there is continuity - but not between the copper and where you have put the lower left circle. What has caused this? I haven't overheated that join, haven't ripped through it with a chainsaw - why has the trace done that? Can I trust the rest of this PCB?

I can easily bridge those points and that was my plan - but what has caused this?
Click to expand...
I have never had a Trace lift but nothing is perfect.
I think it's just a one off, I would just jumper it & finish the PCB.
 
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Hmmm... I'm still uncertain as to which type of 1µF I should use. I guess Tantalum will be fine and i imagine that at the positive end should go to the pin 7 side. And C12's positive should go to the diode side?
 
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Music6000's recommendation is fine. If you choose to use tantalum, the - side on both goes toward the diodes.

Hard to tell what's going on at the damage site. For a photographer, that's a pretty shitty pic. Got a macro lens? :)

I gotta say that I have never received a bad board from PedalPCB, but shit can happen. It takes a far amount of abuse to break a trace on one of these boards. Since we can see Cu thru the solder mask, whatever happened, it happened after the solder mask was applied.
 
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I am building one of these right now and have the thinner WIMA 1u caps but they were just barely too large. I ended up using MLCC (it's not finished yet, gotta get some transistors still) I haven't finished it but I took a look at previous build reports and they appeared to use MLCC.
 
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