Revel no 9v on IC1?

[jwin615]

Limited building time lately +working on learning illustrator and etching has lowered my output. I swear, since I started etching it's been a curse. 1 etched pedal has worked properly.
Anyway. I have a Revel that isn't getting 9v on IC1. Just nada. LED IC2 are getting 9V. Vref correct on IC2, but appears as 1.1x volts everywhere on the lower half of the PCB(IC1, Q1, Q2).
There's on scratch on the silkscreen/mask that runs from R4 to Q1 collector. That's the only thing I can find.
Cant figure out why the top half of the board is good and bottom is crap...
Same with and without ICs, with new opamps from mouser.
If I jumper VCC to IC1, it does pass audio but only slightly above unity with everything cranked.
I did replace C100 a few weeks back before I shelved this before I realized only half of my power was messed up.
Not my prettiest soldering. First board going from a micronchisel to a beveled tip. Don't think I care for it.
Anyway, that's for reading and looking.

 

[owlexifry]

with a multimeter, are you getting continuity from the cathode (-) side of the 1N5817 pad to:
- pin 8 of both ICs?
- collectors of both Q1 + Q2?

 

[jwin615]

with a multimeter, are you getting continuity from the cathode (-) side of the 1N5817 pad to:
- pin 8 of both ICs?
- collectors of both Q1 + Q2?

Thanks for the reply @owlexifry
Doubtful at IC1 since there's 0 volts on pin 8(headed to work). But jumpering pin 8 to pin 8 and it passes audio. But I don't get having VCC and Vref at one point but not another. It seems like a short/damaged trace but I would think I would see a voltage drop everywhere. Especially on a 8.95 volt battery. Maybe that one scratched area(Q1E to R3) which looks like ground plane, is the smallest of shorts to ground? But having Vref present on IC2 makes me think that's not the issue either.

 

[Robert]

I wouldn't be too concerned about the soldermask scratch. If there was a short to ground it would pull the entire 9V supply down, not just a portion. Scratching soldermask doesn't really affect the PCB unless the scratch cuts through the copper. You could sand the PCB down to bare copper and it'd still work fine as long as you don't have any solder bridges.


There is a trace running from C100 that powers the lower half of the PCB. If that trace got damaged while replacing C100 it could cause the measurements you're getting.

Do you have 9V on C100?

If so, run a jumper from C100 to pin 8 of IC1.

If not, run a jumper from C100 to pin 8 of IC2.

Or just jumper pin 8 of the two opamps together like you found and say "F**K you!" to science...

Either option accomplishes the same result.

 

[jwin615]

I wouldn't be too concerned about the soldermask scratch. If there was a short to ground it would pull the entire 9V supply down, not just a portion.

Do you have 9V on C100?

If so, run a jumper from C100 to pin 8 of IC1.

If not, run a jumper from C100 to pin 8 of IC2.

Thanks Robert. I'll try to give it a look before heading out this morning. I feel like the answer is yes, 9v is present. Any thoughts on why Vref would also be off on IC1 but not IC2?

 

[Robert]

IC1 could be sinking VREF since it has no VCC to operate properly.

VREF is pulled up across a 10K resistor so it wouldn't affect IC2.


There could, of course, be other traces damaged.