Boss CH-1 Help - No Effect/Very low wet signal!!

[aliceinchains88]

Hi! I'm new to the forum, I got to this place when I was looking for a solution to my problem, and I found a topic with a very similar issue, but it was unresolved. I see there is a lot of experienced people here!

The thing is that I bought a broken analog CH-1 to repair it myself, the problem was (at first sight) that there is no effect when the pedal is triggered on, only dry signal all the time.

After a little investigation, I found out that there is actually a wet signal at the output, but it is so low in volume that it cannot be noticed in the mix. I realized this by connecting both ouputs of the pedal to two different amplifiers. When connected in stereo, out B is OK, always dry signal, and out A has no perceptible output.....except when I turn the master of the amp all the way up, the wet signal appears!! but it is so weak that it can be barely heard.
This wet signal is affected by the action of the pots, I can change the depth and EQ by turning the knobs.

I have checked the most common issues:

1- I measured the Q2 (bypass fet) drain-source impedance to see if the bypass is working, seems to be ok (about 360ohm when on and more than 1Mohm when off)
2- I replaced the MN3007 IC with another I had from an older project, and problem is still the same. Considering this plus the fact that I do get some wet signal, I think the LFO and the delay parts of the circuit are working fine.
3- I tweaked the bias trimpot (R16 I believe) and it doesn't produce any substantial variation (it does distort the wet signal when it's all the way up).

I have also read something about the bias resistors for the LFO (R42 and R47) to be swapped and with wrong values, but when I swapped them, I killed the poor wet signal I had, so that's not the problem.

Any ideas? I would REALLY appreciate your help/comments/suggestions, maybe this will help others with the same issue.
I don't know if i can post links to other sites, I have the schematic and layout, and the related topics I found here and in other forums.

Thank you in advance!

James

[Fender3D]

If Q2 is ok (you may sub it with Q1) check if the E. Level control is ok (you may short its 3 lugs).

sadly without the proper tools (scope) it will be a hard job nailing it down...

[aliceinchains88]

Fender3D, thank you for your answer. Sorry I couldn't reply before.
I shorted the effect level pot leads like you proposed, but it didn't change anything. Actually, I shorted the leads of all the pots without success, nothing changes. The only interesting thing is that the EQ, RATE and DEPTH pots affect the delayed signal at out A (a vibrato-like signal), but the E.LEVEL pot does NOTHING to this signal when I turn it. I measured its impedance variation and it is ok. I believe this should at least vary the volume of the wet signal.
Unfortunately I don't have a scope handy, and even if I did, I don't know how to use it 

I also measured the DC voltage at all the ICs. This is what I have:

Opamps:
IC1
1- 4.25
2- 4.25
3- 4.18
4- 0
5- 2.11
6- 4.27
7- 4.27
8- 8.49

IC4
1- varies between 3.3 and 4.2
2- 3.8
3- 3.8
4- 0
5- varies between 3.3 and 4.2
6- 3.4
7- varies between 3.0 and 4.8
8- 8.37

IC5
1- 4.23
2- 4.23
3- 2.07
4- 0
5- 4.17
6- 4.19
7- 4.19
8- 8.42

BBD and Driver:
IC2
1- 7.3
2- 3.84
3- 3.95
4- 0.49
5- 0
6- 3.76
7- 4.6
8- 4.6

IC3
1- 7.28
2- 3.75
3- 0
4- 3.8
5- 0.4
6- 6
7- 2
8- 0.48

I used a 9V battery measuring 8.67V connected to the battery clip of the pedal and with both outputs connected.

I hope this helps a little.

Anyone else? any other suggestion?

Thanks a lot!!


James

[Govmnt_Lacky]

It sounds like your problem may lie somewhere in the EQ/ E. Level area. The lower voltage on Pin 3 of IC5 could be a clue.

Try checking you wiring between the main board and the control board (one with the pots) and also check that the E. Level pot itself is good.

Try measuring voltage again at IC5 Pin 3 while adjusting the EQ and see if the voltage changes.

Good Luck 

[Fender3D]

Voltage at IC5's pin 3 is strangely low.
You may unconnect E. Control's lugs 1-2 and use them as a signal probe bypassing IC5a and Q10:
connect them to IC2's pins 7-8, it won't work properly, but at least you'll realize whether you have a proper signal from BBD.
Whether signal remains low, then you have issues BEFORE BBD

[aliceinchains88]

Hi people, good news, it works!!!!

I have improvised an audio probe and tested diferent spots to see if I have a good wet signal. I tested the outs of the EQ and LEVEL pots (pcb pads 15 and 16), and I had a nice full-volume wet signal!! Also checked the emitter of Q10 with the same great result!!
So I kept checking, IC5 was OK at pins 1, 2 and 3, pots were OK, then I checked C40....I had no signal AFTER C40, so just changed it for a brand new 1u/50v capacitor, plugged in and that was it, full chorus effect on output A!!

Then I kept testing with the probe, and I see that R50 (connected after C40 and into Q2) with the effect ON I have no signal after it (actually it is the same weak signal heard only with vol all the way up), and I do have full wet signal after R50 when the effect is OFF.
That is something I don't fully understand, since I should always have wet signal after R50 and it should be "muted" by the large impedance of Q2 when the pedal is OFF.
Also checked the voltage at pin 3 of IC5 and it's still +-2V, which seemed to be too low voltage. Beside this, the effect works fine...for now.

Considering all this, is there anything else I should check, just in case?

Anyway, I'm very happy because I finally figured it out! Thank you people so much for your support!!


Kind regards from Buenos Aires, Argentina!

James