Dirty Sanchez - impasse

[pdfermat]

So I think I’ve isolated the problem to somewhere in the IC3 loop, but can’t figure out where exactly the problem is. Signal is good coming into pin 2, and nearly gone coming out of pin 1. I’ve verified all the components are correct, swapped for a known good IC, and can’t see any solder bridges in the area (or anywhere). Pin voltages on IC3:

1: 7.89v
2: 7.64v
3: 8.43v
4: 0.0v
5: 8.37v
6: 7.80v
7: 7.89v
8: 8.43v

Any ideas?

 

[Nostradoomus]

What are your other IC voltages? These are pretty much all wrong and should be around 4.5v barring pin 4 and 8

 

[pdfermat]

What are your other IC voltages? These are pretty much all wrong and should be around 4.5v barring pin 4 and 8

IC1
1: 4.42
2: 4.42
3: 4.21
4: 0.0
5: 4.42
6: 4.42
7: 4.42
8: 8.41

IC2
1: 4.42
2: 4.42
3: 4.38
4: 0.0
5: 4.40
6: 8.42
7: 8.41
8: 8.41

IC4
1: 7.89
2: 7.87
3: 8.41
4: 0.0
5: 7.81
6: 8.05
7: 8.04
8: 8.42

 

[Nostradoomus]

Are the ICs firmly in their sockets? Maybe try swapping IC 2 for one you know works. Voltages are good until IC2 pin 6. Double check all your values and soldering around the power/VREF sections. Is R13 220K? It could just be the lighting making it look funny. R101 and R104 as well, doesn't look like 20k.

 

[pdfermat]

Are the ICs firmly in their sockets? Maybe try swapping IC 2 for one you know works. Voltages are good until IC2 pin 6. Double check all your values and soldering around the power/VREF sections. Is R13 220K? It could just be the lighting making it look funny. R101 and R104 as well, doesn't look like 20k.

ICs re-seated with known good ones. No change. R13 is indeed 220k, but I’m getting weird readings from R101 and R104. Maybe I should try to measure those from the back and possible replace components in the 2nd IC2 loop.

 

[Stickman393]

IC2 is generating the strange voltages you're seeing on IC3.

there are three resistors to be concerned with here: R104, R105, and R106.

R104 and R105 are the most important: they form a voltage divider you should see about 5 volts to ground at the point where those two connect.

I suspect that r105 is a 330kohm resistor. If that was the case, I'd expect to see about 8.44vdc at the junction between r104 and r105 with a supply voltage of 9vdc. It's hard to tell though, as the photo is too dark to make out the colors.