Crybaby Idiot Wah Problem

[homer1co]

I have been messing with my Dunlop GCB-95 Wah (I don't know why, don't ask). Installed Fasel, and tru-bypass and replaced a few resistors for tone. It was working perfectly, until I decided to install a 12 volt LED indicator, which worked when hooked directly to a 9-volt source. My bypass involved a 3-way switch, and somewhere during installation, my Crybaby died. The bypass still works, but that's all folks. Like the idiot I am, I was probing with the LED, 9-volt connections, and an ohmmeter to the switch while the unit was hot and hooked up to my system. It appears I smoked something on the board, but I don't have a clue what. I tested the transistors and the resistors with said meter, and they check out OK. I even changed out the inductor for a known good one. I know I can replace the board for $20, but this is the second one I'm working on (I really f**ked up the original). Does anyone have any ideas what component I may have smoked.

[xFallen]

What LED works for any length of time at 9VDC? The highest foward voltage device I found was 4.6VDC. Typical red LEDs are like 1.5 VDC. They all need a dropping resistor, generally, to limit the current the diode junction sees.

Does the LED still work?

It could be anything, really, including the stomp switch.

A safer way to trace the circuit is to probe the signal path with a low level audio signal tracing the circuit backwards from the output jack toward the input jack while plugged into a small amplifier. The output from a small radio will do the trick, or there are ways to use one's computer soundcard output. Check the web for instructions, or maybe it is here somewhere.

Just please be careful or you may end up frying something else. Sounds like you're having a run of misfortune.


Barry

[Baxthorpe]

If you are probing for the signal, don't forget to put a capacitance in series with the probe to decouple the DC.

I sounds like you inadvertently killed a capacitance. If the one associated with the inductance dies, the thing usually turns into a swell pedal. No sound, and you have to look at all the others - where the signal dies, the miscreant lies ...

[homer1co]

Crybaby Idiot Wah

I was probing for 9 volts and ground at the stomp switch while wah was hooked to sound system. I was probing with both DVOM and the diode itself. The diode still works, but I removed it from circuit. I got it to work by grounding it to the case and running the hot through the stomp switch. Could I have smoked a capasitor?

[52 Bill]

The only things that may have been damaged by probing with 9 volts are the transistors, but even they are blocked by caps at both the input and output.

Unplug everything and diode test the transistors with your meter. Test the switch and the wiring going to it. An open coil will not cause the circuit to die, just not wah. Check for solder bridges on the board and for bad solder joints. If your wah has the plug in wiring harness, check the push on connectons at the plug. If it has the soldered on wires, check them for broken connectons. If everything tests ok and still no sound, power it up and check the voltages on the transistors.

Hope this helps.

[homer1co]

Crybaby

Thank everyone for taking the time to address my little problem. I did as 51 Bill suggested and traced the voltage with the unit hooked up. I have 9 volts going into the power transisor and 3.36 coming out, with 2.36 as the trigger. I traced the 3.36 to a capacitor. There is only .63 volts coming out. Is this my bad guy?

[52 Bill]

I don't know which cap you are talking about, but it sounds like you are reading the voltage coming from the following stage, not through the cap. There should be no dc voltage bleeding through any cap. Just like in tube amps, these caps are designed to let the sound signal pass, but block the dc voltage from stage to stage. Sometime they are referred to as blocking caps.

Try unsoldering the low voltage side of the cap and then read the voltage on the second side of the cap. It should read nothing or next to nothing. If you do read a dc voltage on the open end of the cap then replace it.

[Steve Conner]

Why not just replace all the transistors and the diode? They're only a couple of pennies each.