Jim Dunlop crybaby GCB-95 Problem

[Zito]

My crybaby is a 1994 GCB-95

I bought it used.

My guitar signal is fine but when I step on the it to Wah it goes completely dead!

My battery reads 9.20 Volts (it's new)

As far as I know this Crybaby is totally Stock, although it has a HotPotz-II in it. I don't know if they came like that or not.

[Aharon]

When I bought my CryBaby years ago it had a similar problem.
Ended up being a crack in a trace on the PCB.
I would start by checking if there's voltages where it should be like transistors.
Other than that a I would rig a signal going through it and see where it stops.
If you read the Technology of the Wha at GEO it also mentions caps a a possible problem.
Aharon

[Zito]

The traces on the board look perfict.

I have voltage at across all three transisitors although I'm not sure what they should be.

I'm now hunting down how to check the caps with my DMM.

[p1_ind]

Don't forget to check the switch or the output wire of the effect to the switch (which I think is a blue wire coming from the pot).

Adam

[Zito]

I checked the switch and and the wires from the back of the board.

Purple to green when the wah is off.  It is good.

Switched the wah on and checked purple to blue and that is good also.

I continued to check the rest of the wires (black and yellow) from the solder point on the back of the board to the HotPotz II and they are good.

I'm back to hunting down how to check a cap.

[Zito]

I made an audio probe and trace the signal to first component (a diode I think) and the signal dropped way off.  

I continued to trace the signal to the middle leg of the first transister (in the buffering area) and there was no signal from either outside leg of that transister.  

Is that transister bad?

[smoguzbenjamin]

Almost no signal at the base, and NO signal at the emitter or collector? Busted tranny. I think the first component would be a resistor though, which would explain the loss of volume. Try replacing that transistor, without damaging the copper tracks. They tend to let go when you overheat them.

[william]

I'm having a similar problem but when I probed it the signal stopped after the first Cap of the buffer.  I was getting a clear signal before it, but nothing but a pop when I connected it to a probe.  Is it common for a cap like this to malfuction?

[smoguzbenjamin]

Cap problem. All you need do is replace that cap and you're hopefully back in business

[Zito]

Does the voltage of the cap matter?  

Could I use a 50 volt .01uf cap?

[Ed G.]

Does the voltage of the cap matter?  

Could I use a 50 volt .01uf cap?

That would be fine.

[Zito]

It wasn't the 0.01uf cap.  

After replacing it (0.01uf), using the audio probe it had that same hollow sound and loss of volumn right up to the base of transister MPSA13 and no sound at the collector or emitter.

Time to order a MPSA13 and try again.

[Zito]

Well I got my parts and replaced the MPSA13 and still nothing past the center prong on the trany (base I think).  

The voltage on the one side of the MPSA13 trany is 0.79.   Does that sound correct?

[Zito]

I Changed over to the true bypass and got rid of the the input buffer.

I now have good sound in bypass but when I hit the switch I get just a faint thin sound and no Wah when I rock the pedal.

Suggestions?

[brett]

Time to order a MPSA13 and try again.

Shouldn't that be an MPSA18 ??  An MPSA13 is a Darlington pair, with hFE of >5000.  An alternative for an MPSA18 is a 2N5089.  When you've got the right tanny in there, check that the base (middle leg) voltage on the first transistor is a reasonable value (something like 1.5 to 2 V).  The emitter (left leg when looking at the flat face, I think) will be 0.7V less than the base.  The collector (probably the right leg when looking at the flat face) will be more like 3 to 6V.  There should be a small signal on the base and emitter and a very large signal on the collector.

[Zito]

The MPSA13 was in the input buffer and was removed when I changed over to the true bypass.

Q1 MPSA18
Bass voltage is 0.17V
Emitter voltage is 0.00
Collector voltage is 0.66

Q2 MPSA18
Bass voltage is 0.45
Emitter is 0.79
Collector is 0.00

Voltage after the wall wart plug and before the 1K resistor is 8.93V and after the 1K resistor it is 0.79

When I measured the 1K resistor with my DMM it read .974 ohms

[Zito]

Bumping this to the top.

I'm really lost here.

Still no Wah just a hollow sound in the wah position.

[Fret Wire]

Since you already modded your's, use this as a reference, and double check that all your connections are correct:

http://homepage.ntlworld.com/s.castledine/greenfuz/wah.html

[Zito]

Fret Wire,

That is the exact link I used to mod my pedal.  I removed the input buffer components as I thought it would be a much cleaner job.  I rechecked the mod and it is perfect.

It seems as though I have a voltage problem as my voltages on the MPSA18s are no where near close to those posted by Brett earlier in this thread.

Following the neg. battery (black) wire to the board my voltage drops after the 1K resistor to 0.79V.  Before the 1K resistor it is 8.93V.  I removed and replace that resistor, but that didn't help.

I got this wah in non working condition and it would only work when the effect was bypassed.  After I made the mod I got a very faint sound in the effect position but no wah effect.  

I thought repairing and moding this wah would be a good place to start learning before I actually tried to build anything from scratch.  I can't believe how good this board is and much I have learned from from the links and ALL the people who are helping me with this as I know less than nothing about this stuff.

OT.  I live in Western New York.

[Fret Wire]

I'll check the voltages on mine and compare. Western NY, huh? We got pounded with snow last nite!