Twin Peaks Tremolo troubleshooting help please

[AntKnee]

Edited after realizing I shouldn't use IN/OUT in the typical wiring.

I am using the "SND" as the input and the "RET" as the output.

I have no output signal. After probing, with tone at 50%, I have dry signal at both octocouplers, but nothing at C7 or C8, or anything after that in signal path.

My tap switch and LED are functioning and LED1 is lit.

My voltages look fine to me, but please feel free to check these:
TL074
1- 4.5
2- 4.5
3- 4.5
4- 0
5- 4.5
6- 4.5
7- 4.5
8- 4.5
9- 4.5
10- 4.5
11- 0
12- 4.5
13- 4.5
14- 4.5

LM356
1- varies
2- 3.3
3- 3.3
4- 0
5- 3.3
6- 3.3
7- varies
8- 5.0

TAPFLO
1- 4.95
2- 2.3
3- 2
4- 5
5- varies
6- 1.5
7- varies
8- 4.95
9- 2.5
10- 2.8
11- 2.2
12- 4
13- 2
14- 0

T1: O= 5, G= 0, I= 9.3
T2: O= 4.9, G= 0, I= 9.2

Edited after realizing I shouldn't use IN/OUT in the typical wiring.

[AntKnee]

Also, with my JMK test rig, I can crank my test tone volume and headphone volume way up and just barely hear the effected signal. Like if it were bleeding through somewhere. At this point, I have verified my component values are correct.

[bsoncini]

I have a working I haven't fully boxed up yet. I'll post my voltages tomorrow.

[bsoncini]

Do you have audio before the ldr? And after the ldr? Are c6 and c7 bipolar? Have you tried another tl074?

[drolo]

Hi Anthony,

can you check if your optocouplers are correctly oriented?
Check if you are getting a voltage variation on the LED side of the optocoupler and a varying resistance on the LDR side.

It might be just typo but can you check if you used a LM358 and not LM356?
Also voltage at pin 8 of that opamp seems low. It should be 5v + you LED voltage drop. Can you double check ?

pin 4 on your tl74 should be close to 9v. Can you double check your voltage?

[AntKnee]

I believe my octos are correctly oriented, I matched up the + on the component with the symbol on the pcb.
I am getting slight variation on the LED side, from 1.40 to 1.44, back and forth.

I did use LM358.
Pin 8 of that is 6.8v, must have been a bad reading earlier.

Pin 4 of TL074 is 9.2, I misread my notes.

[drolo]

ok that makes more sense at least :-)
could you try to measure the resistance of your optocouplers on the LDR side (on and off, use the square wave setting at full depth)

[AntKnee]

On square wave, full depth...
The LED side varies from 1.29 to 1.46
I'm not getting any reading on the LDR side, but I'm not sure if I am measuring it correctly. I am using the resistance setting on my meter and touching the probes to the two LDR legs of each octo. Is that right?

[drolo]

it might not work with every multimeter, measuring resistance in circuit while operating
in theory the optocouplers should be working, you have some voltage going into them.
If the signal stops after the optocouplers, you may have some short somewhere in that area

[AntKnee]

David, I sincerely thank you for your help.
I'm done with this for today. I'll check it over with fresh eyes and report back tomorrow.

[AntKnee]

it might not work with every multimeter, measuring resistance in circuit while operating
in theory the optocouplers should be working, you have some voltage going into them.
If the signal stops after the optocouplers, you may have some short somewhere in that area

I rechecked all joints and components and don't see any shorts. I have audio at on leg of the LDR of the octocoupler, but no audio at C6 and C7. Looking at the schematic, it looks like this would be where the failure is since C6 and C7 come directly after the octocouplers. I pulled C6 and C7 to rule them out as a short. I am not getting any audio at their solder pads. Should I be able to hear audio with a probe there? I am using VTL5C1 vactrols. Like you said, they are getting voltage and audio, so it seems they should be working.

[drolo]

if you pulled the 2 caps out, now is a good time to measure the resistance of the optocouplers. Try to measure how it changes using the square wave at full depth with a slow rate your multimeter can cope with

[AntKnee]

if you pulled the 2 caps out, now is a good time to measure the resistance of the optocouplers. Try to measure how it changes using the square wave at full depth with a slow rate your multimeter can cope with

I was able to get a measurement now. I get varying resistance on the LDR side, from 0 to 30m.

[drolo]

very strange ....
you said you had signal up to one leg of the LDR, is that thr left side, and then nothing on the right side of the LDR ? (if facing the PCB component side)
maybe some shorts to ground after the LDR's?
Just to rule out the possibility of the optocouplers having some issue (which I doubt) can you bridge the LDR's with a 1k resistor. and adjust the volume trim pot to see if you have any output

[AntKnee]

It is the same on both LDRs. I have tone set at 50%, on classic mode.

Am I correct that if the octos are working properly, I should hear audio with a probe at C6 and C7?