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

 

[ADAOCE]

They are about 4.7k less than the ohm reading on the other side of R101... makes sense

 

[Chas Grant]

That is alright, the only time when everything goes right is when your not trying

 

[Chas Grant]

They are about 4.7k less than the ohm reading on the other side of R101... makes sense

If you go from one side of R101 then the other side of R101 then about 4.7K is right, thats R101

 

[ADAOCE]

Thank you for your help I really appreciate it. I am learning a little here... I think. So could a bad component be causing the open circuit?

 

[ADAOCE]

4.7K is right, thats R101

Yep that’s what I thought

 

[Chas Grant]

Yes it could, but if you took at the schematic, measuring from the 9V pad to ground pad, there are only 3 components, the 1N5817 R101 and R102. If you measure them you get ok values. If you can, try to measure the 3 components from back side of board, try to stay on solder joints only, not the leads of the components. And check the diode both ways, one way should be resistance and the other an open.

 

[ADAOCE]

Ok so I get OL and 9.6k on the diode. I get the right resistance values on 101 and 102 as well but it’s difficult to keep a consistent reading trying to touch the solder instead of the component leads. Touching the leads it’s the right value and is consistent

 

[Chas Grant]

You should get clean readings on the solder pads, unless the solder joints are cold. Zooming in on the pics they get blurry, and on some the joints look ok and on others I can clearly make out the lead, which could be a cold joint. Try to reflow R101 and R102. After touching the joint, wait till you see the solder melt, then count to 3 or 4 before removing the iron. No pause or Mississippi's on the count, just a normal 1 2 3...

 

[ADAOCE]

Ok I’ll go give that a shot... gotta get some heat my garage lol

 

[Chas Grant]

I hate winter time!!! Luckily I have a work space in my house.

 

[ADAOCE]

I hate winter time!!! Luckily I have a work space in my house.

I’m working on that!

 

[ADAOCE]

Reflowed R101 and R102 and D100 and there’s no change

 

[Chas Grant]

WTF

 

[Chas Grant]

OK lets check continuity of board,
BTW I'm not used to taking this kind of a butt whooping from electronics, so its a good one.
If you measure between the colored circles, you should have near zero ohms readings

 

[ADAOCE]

Yes to all circled points for continuity

 

[ADAOCE]

I’ve built pedals that looked way worse than this and work flawlessly (Angry Andy Plus). This one is definitely puzzling

 

[Chas Grant]

I doesn't look bad, a good cleaning does wonders. And you have continuity on all those points, this should work

 

[Chas Grant]

...but it doesn't

 

[ADAOCE]

Think i have to call it for tonight. Thanks again for trying to help me out. I’ll try plugging it all back in tomorrow and seeing what it sounds like but without that Vcc/2 after the divider it really should NOT work right?

 

[Chas Grant]

I have a hunch, but no way to prove it, and its based on something I have only seen a few times. You could have a flakey component. Its rare but it does happen. I once troubleshot a bistable amplifier for 2 weeks before I found a component that would fail, and only under certian conditions. After replacing it the circuit worked fine. We have 3 suspects but no way to confirm definitely