Mach 1 no sound when engaged

[ADAOCE]

Have a Mach 1 that has no sound at all when engaged. Bypass and LED work fine. I’ve checked my solder joints. Didn’t see any cold looking joints. I touched up a few resistors so that the solder penetrated both sides. I even tried a different opa2134 and a tl072.

I’ve recorded the following IC voltages with the opa2134

1: 4.46
2: 5.03
3: 0
4: 0
5: 0.16
6: 0.59
7: 4.46
8: 8.2

I’ve attached some pictures of the board from the top side. I know it could use an IPA wipe down but to be honest that’s never resulted in an issue like this for me and I’ve done ones that looked worse.

mill have to wait til tomorrow to get a picture of the underside (I stupidly didn’t take a picture when I pulled it out to reflow joints). Underside looks better than top though since that’s the side I soldered from.

anyways I’m just hoping these ic voltages are enlightening. TIA

 

[Chas Grant]

See if you can get black lead on pin 4

 

[Chas Grant]

That way you are referencing battery negative

 

[ADAOCE]

That’s how I e been measuring the divider and R3. Black lead to pin 4 and red lead to test point

 

[Chas Grant]

And you have 0 volts on R3, on the side near pin 6it should be battery voltage

 

[ADAOCE]

Yes it’s 0 on both

 

[ADAOCE]

I’m measuring the wrong one hold on!

 

[ADAOCE]

Ok i get 9.3 on ic 6 side and .64 on the other side of r3

 

[ADAOCE]

9.3 on outward side of R4 and .56v on other side of R4

 

[Chas Grant]

Ok that’s better, gotta look at schematic real quick

 

[Chas Grant]

Check voltage on pin 7 real quick, just want to verify the feedback path

 

[ADAOCE]

.56v pin 7

 

[Chas Grant]

The voltage on pin 7 should be higher

 

[ADAOCE]

Ok so what might that indicate?

 

[ADAOCE]

Maybe something from C2 and to the right or R4 is pulling it down?

 

[ADAOCE]

0v on the other side of C2. Sorry just trying to give you info

 

[Chas Grant]

No I was pondering that. C2 is a coupling cap, it passes the AC signal but blocks the DC from the op amp circuit. If that cap shorts you get a loud hum out of pedal, that hum is the DC

 

[Chas Grant]

You have a short somewhere, question is, where?

 

[ADAOCE]

So the last time I played through the pedal the clipping section sounded great so I think that was working ok but the volumes were all off and I had to basically dime out volume and drove pots and then the tone pot actually made it louder as well

 

[ADAOCE]

Or at least made it appear louder. The volume pot had the worst behavior. It felt like tone and drove we’re doing what they were supposed to but volume was almost nothing unless cranked

 

[Chas Grant]

Shouldn’t have to dime it out though, that could be do to the low voltage on pin 3 and 6