Speedball upgrade - small board: One LED not lighting, one V reading out of spec

[Paul Birkeland]

Oops, looks like I didn't add the attachment.  It should be visible now.

[Luxifer]

No worries, thanks for linking that.

I tried reflowing the solder in the blue circle (back of 1A) which didn't give me the large voltage reading you mentioned I should expect out of 0B. I think you might be right that the pad/contact in the red circle is the culprit.

Given that, what would you suggest I try?

[Doc B.]

It's difficult to see what the condition of the trace leading to the pad in the red circle is. Looks like the solder did not flow well there. If the trace and pad are OK that connection should just need to be reheated until the solder forms a fillet at the lead and pad junction. There may just be excess flux under the solder that is keeping it from flowing across the pad and a reheat with the addition of a tiny bit more solder could fix that.

If the trace or pad is visibly damaged the way to deal with it is gently scrape back the green solder mask from the trace where it is intact, cut a short piece of wire and use it to bridge from the end of the transistor lead to the exposed trace, soldering it to both the bare trace and the transistor lead. But don't try that if the trace and pad looks OK, only resort to that if it is obviously damaged.

[Luxifer]

I may be not seeing it, but the pad in question doesn't look to be connected to any trace. What does this mean for how I should proceed?

I tried to clean up the flux with a bit of 91% IPA, and took photos through a 4x magnifying glass, so you might have a better look at the condition of the area. See here: https://imgur.com/gallery/w9T8ztb

I have since added solder to and reflowed that leg, but I am still not getting the correct voltage reading at 0B (remains in single digit mV).

For some reason, I had a hard time getting the solder to form a fillet, it just kept running through the PCB and beading up on the other side. I'm not sure if that's significant, but I thought I'd mention it.

[Paul Birkeland]

The trace is up top. There is a hole in the trace, then a solder pad on the bottom side of the board.  The two are connected with plating that goes through the hole.  I think the pad on the bottom of the board is gone, and possible the through plating in the hole.  You may be able to solder it from the top of the board though if that pad is still there.

[Luxifer]

Ah, I see the trace up top, sorry to have missed that.

Should I try to scratch away the solder mask, as mentioned, or should/can I just wire the damaged leg directly to the far leg of the part in Q2B, where that trace terminates?

[Paul Birkeland]

Either one is an acceptable workaround. 

[Luxifer]

I just tried wiring the two legs together by hand, but I am still reading in the mV range at 0B, with the white wire removed. Is this definitely incorrect?

If so, what do you suggest I do next?

Here is a photo of the wiring, to confirm: https://imgur.com/gallery/ZrHfWvW

[Paul Birkeland]

It's probably time to contact replacement parts to get some fresh parts and a new PC board.

[Luxifer]

Ah, I was hoping it wouldn't come to that, but fair enough.

Will I need the small PCB and all of the parts that go on it?

[Paul Birkeland]

Yes.

[Luxifer]

Ok, I emailed about getting replacement parts.

Meanwhile, I tried wiring the other two legs of the PN2907 to where their traces led. Unfortunately, that did not solve the problem, and after about 30 second of being plugged in, I heard a loud pop...

I'm not sure what caused this, and am worried I may have caused some other damage. I turned the system off, and checked the fuse, but it looked intact. When I turned the system on, the LEDs lit up, which makes me believe that the fuse must not have popped. Something has changed, however, as now all of the wired spots on the small PCB, 0A through to 0B, read very close to 0mV.

I feel like a huge idiot now, but thought that it might have been another leg of the PN2907 that had a bad connection, and that I could troubleshoot that by wiring, using the traces as a guide.

Do you have any idea what might have happened? Do you think that whatever damage I caused is confined to the small PCB, or might I have affected something else?

[Paul Birkeland]

I would recommend putting the 22K resistors back in.  Please consider that small PC board ruined and promise me that you'll throw it away. 

[Luxifer]

Haha, I promise. I have already ordered the replacement.

If I put the 22k Ohm resistors back in, should I just run all of the voltage checks for the stock final build?

[Paul Birkeland]

Yes, do recheck the voltages.

-PB