Crybaby GCB 95 - Help to debug it !

[Samy]

I have a crybaby to debug it, it belongs to a person i know and the pedal stopped working.
I´ve build the audio probe and tried to follow the signal to see where he died, well ... after the second resistor there is a 0.1µF cap, after that the signal is gone ! I´ve replaced that cap but i have the same problem, no signal at all. After the cap there is one transistor the mpf A18 ...
I can´t find the crybaby schematics and if you can point me where to find it, it would be very helpfull.
Any tip ?

Thanks.

[Seljer]

Here is the Crybaby:
http://www.geocities.com/CollegePark/Library/1355/crybaby95.gif

the only .1uF cap there is part of the power filtering, theres no audio signal going over it

[Samy]

Thanks.
My mistake , it´s a 0.01µF cap  after the 68K resistor.

[Thomas P.]

Battery operation?

[Samy]

Battery operation ??
I´m using a 9V regulated PS .
Something is sending the signal to ground after the 0.01µF cap, or .... i might have a problem related to the DC feeding the circuit ... i can´t measure voltages higher than 0.3V , only exception when measuring after the DC Jack

[Thomas P.]

I asked because most of the time (100% of all "broken" dunlops I bought at ebay) the solder joints of the dc-jack are broke.

[Paul Marossy]

Here's some ideas:

1. Do you have a signal between the 0.01uF cap and the first transistor after the buffer? If not, then maybe your first transistor crapped out.
2. Are you sure that the wiring harness is properly connected to the PCB or that all the wires to the connector have continuity between and whatever they connect to?
3. Have you tried using a battery to see if anything changes? I bought a wah off of ebay once that was "broken". The only thing wrong with it was the power jack was a little corroded and power wasn't getting to the circuit. Cleaned it up and it worked great.
4. Have you removed to PCB to look at the back side? Maybe there's a faulty solder joint.

EDIT: And what tomboy just wrote...

[Samy]

There is no signal between the 0.01µF cap and the first transistor. Theres is no buffer, this pedal was modded to true bypass and the buffer components aren´t present, the input signal is directly connected to the 68k resistor.
I will Check the DC jack on Monday i try to use a battery but i have measured 9V on the pcb after the DC jack and just before the 9 V zener , after that the voltages are very, very low.
I´ve looked also  the back side of the pcb, everything seems ok.

Thanks for the tips, i will keep you informed about my debug progress.

[Paul Marossy]

No input buffer, huh? Did you just true bypass it?

[Samy]

No, the buffer components aren´t there, the input wire is connected to the 68k resistor and the pedal was working.

[Paul Marossy]

OK, well then, it sounds like the power supply is the place to look for your trouble.

[Samy]

I´ve found a braked circuit trace and repaired it, now i have 9V almost everywhere.
The signal now flows after the 0.01µF cap but doesn´t go trough the MPSA18.
Is there any MPSA18 equivalent ? Any close ones should do the trick, it´s just for testing.

Thanks.

[Paul Marossy]

Is there any MPSA18 equivalent ? Any close ones should do the trick, it´s just for testing.

BC109s are around the same Hfe. You could also try a 2N5088 - might be a little high on the Hfe, but not by too much.

[Samy]

Thanks Paul.
I´ll see if i have some of those to try it.

[Samy]

Thanks for all your help, i found the problem, it was the zener diode !!!
I don´t know why but the other day i was reading higher voltages on the circuit, perhaps i was measuring wrong ( it was late at night  ), today  the circuit was once more dead, i removed the zener and the voltages raised, i plugged the jacks and "wahhahahahaha" ! The pedal was working ...
I should have checked the zener on the first place ! The was quite obvious but a false reading messed all up .

Now ... let´s mod the Crybaby to make it more versatile.

[Paul Marossy]

Huh, I didn't think to check the zener diode, but that makes perfect sense now that you mention it. Good work!  I'm putting this in the mental rolodex.