Guyatone OC-7 octaver clone : issues with octave up

[eh la bas ma]

Hello,

Here is a sound sample to show you the symptoms :

https://soundcloud.com/ehlabas-ma-chaussure/oc-7-issue

This octaver worked perfectly for a year. It suddenly started to misbehave one day.

schematics :
https://www.delykpcb.com/product/up-down-daddy-pcb/?attachment_id=1089&download_file=k0sve9jvlkveb

I already posted a thread about the apparent cause of this issue :

https://www.diystompboxes.com/smfforum/index.php?topic=131025.msg1272492#msg1272492

Sometimes i just have crackling noise issues upon activation, when oct.up control isn't fully CCW. These noises can appear also when the effect was already engaged, if i turn up the octave up.
Sometimes i get a loud fuzzy signal instead of crackling noises, always related to the octave up, with the same pattern (effects is fine unless i turn up the octave up control). Everything sounds ok with the octaves down.

I changed all ICs, all transistors, all electrolytic caps, 3PDT, DC power jack, Oct. Up potentiometer, reflowed many pads, performed lots of continuity tests, cleaned the pcb soldering side with some soldering residue cleaner, to no avail.

Once out of 20 times, the up octave effect works, but it's unstable. No issues with the octaves down, but i suspect they don't sound as good as usual.

Now i am thinking about replacing the diodes.

I know i'm walking blindly step by step here, replacing parts, etc... I know you won't approve this unscientific approach, but using the audioprobe didn't help me narrow it down. This effect is too complex for me to use an audioprobe efficiently, and the issue is unstable. I can't easily test with my audioprobe, while pressing the 3PDT on and off, for exemple.

Do you think a damaged diode could be responsible for the issues described in the sound sample ?

After all the time spent debugging this build without much progress, i ordered a new kit, so i can compare both circuits with an audioprobe and narrow it down. But it will take weeks before i receive the order.

Every observations and suggestions are welcome !

[eh la bas ma]

Here are some voltage readings :


Q1 J201

G= 9.46
S= 9.46
D= 4.60

Q2 2N5457

G= 5.36
S= 5.39
D= 0V

Q3 2N5457

G= 5.36
S= 5.39
D= 0V

IC1 TL72

1= 5.15 8= 9.46
2= 5.08 7= 5.45
3=4.68  6= 5.45
4= 0V   5= 4.88

IC2 LM324

1= 4.84 14= 8.27
2= 5.38 13= 5.15
3= 5.33 12= 4.87
4= 9.46 11= 0V
5= 5.34 10= 5.15
6= 5.38 9= 5.38
7= 5.30 8= 0V

IC3 CD4013

1= 5.70 14= 9.46
2= 3.8  13= oscillating from 0V to 9.46
3= 0V   12= oscillating from 4.50 to 7.50
4= 2.1  11= 3.8
5= 0V   10= 0V
6=oscillating from 2.5 to 5.38 9= oscillating from 0V to 9.46
7= 0V    8= 0V


IC4 CD4013

1= oscillating from 4.35 to 9.46 14= 9.45
2= 9.45                          13= 9.45
3= 9.45                          12= 0V
4= 0V                            11= 0V
5= 0.5mV                         10= 0.5mV
6= 0.3mV                         9= 0.4 mV
7= 0.3mV                         8= 0.3mV

IC5 TL74
1= 5.46 14= 5.46
2=5.46  13= 5.46
3= 5.42 12= 4.99
4= 9.45 11= 0.5mV
5= 5.02 10= 5.42
6= 5.45 9= 5.46
7= 5.45 8= 5.46

IC6 TL74

1= 5.36 14= 5.46
2= 5.37 13= 5.37
3= 4.93 12= 4.94
4= 9.45 11= 0V
5=4.92  10= 4.93
6= 4.93  9= 4.93
7= oscillations between 2.3V and 3.5V 8= 7.55

[ElectricDruid]

Start at the beginning. As you say, blindly replacing parts is unlikely to work, and may well introduce other problems.
It's a big complicated circuit, but actually we don't need to worry about most of it. If the problems are only in the upper octave, then it could be in that filter based around IC1B, or the fullwave rectifier stage IC6D/IC6A. That's *it*. The rest of the circuit is *irrelevant* as far as upper octave problems are concerned.

Problems are possible earlier in the circuit, in the first FET buffer, or the op-amp stage IC1A that comes after it, but we'd expect problems there to show up in the lower octaves too. You can easily check those stages by audio probing the output of IC1A at pin 1. If that's ok, those two stages are fine, and you can move on.
Next probe the filter output, IC1B pin 7. If that's ok, move on to the junction of R13 and R16. You should have distortion (a half-wave rectified signal) there, but your fault was crackling. Failing that, check IC6A, pin 1, the final output for the fullwave rectifier.

At some point along that path your good signal will go away and your problem will show up, and that tells you the problem is between the bad point and the last good point.

HTH

[PRR]

, reflowed many pads...

Did you take it in bright sunlight with a 4X magnifier and inspect the joints??

If the parts/pads are dirty, "reflowing" just moves fresh solder over the dirt/tarnish.