Dunlop Crybaby Wah Help

[Scotty3072]

Hey,

I got a broken Crybaby GCB-95 from a friend to fix.  Everything seems to be connected correctly, and there are no loose wires or poorly soldered joints.  How can i go about finding the malfunction in the unit?  Any help would be appreciated.

Thanks,
Scott

[vanhansen]

Start with an audio probe and work your way through the circuit. You'll find the problem pretty easily that way.

It could be a bad electro cap, lifted trace or solder pad, pad inductor, cold solder joints.  The list goes on.

[sir_modulus]

Heres a good path to trouble shoot:

First off state the problem: you haven't done this yet

Next find the corresponding schematic: Crybaby GCB-95

Now do the basic tests:

1) Inductor test: find the 33k [?] resistor paralleling the inductor (it can be another value, if so, to keep things simple, just desolder and put in a 33k. Now test the resistance across this resistor (it parallels the inductor, so you can check if the inductor has broken (usually inside), by checking if it's open), and you multimeter should read under 100 ohms. (even like 90 ohms is not too good (whe I did mine I got under 10 ohms)). If you get a high value, it means the inductor is open circuited somewhere.

2) Trace test: Go from solder joing to solder joint and test joints that are supposed to be connected for continuity, and the check the unconnected places (ie, the legs of the transistors), so that you know there are no shorts, or cut traces.

That's all I can tell you for now with no symptoms...


Nish

[Fret Wire]

I just want to add that in addition to the above, check the wiring harness that plugs into the circuit board. Sometimes the crimps that retain the wires in the harness come loose. When you describe the problem, find out if the owner used a power supply (describe it) or battery.

[petemoore]

Are the input/output jacks soldered into the PCB ?
 This is a good source for problems to occur, some models are built this way, FWIU.
 If you have a DMM, you can check many debugging items mentioned, including voltage readings that may narrow the problem down quickly.
 Don't try this with lethal voltage potential items like amps, but plug the unit in an amp, start with the output jack tip, and see if you get a buzz sound when you connect your thumb to it [sounds like finger touching tip of live cable], then trace through the signal path of the circuit toward input and see where the sound buzz sound gets lost.
 You could plug a cable in a guitar, have someone strum the guitar, connect the sleeve [other end of cable] of the plug to ground, and the tip, with the signal in it, use that to start from output toward input as alternate source, as it should sound louder than the thumbuzz technique, does the same thing, [better for small Si Amps to use the guitar YMMV], instead of a piece of wire touching your thumb and the circuit points, you need a strummed guitar, a cable, a test clip and a test clip/wire/probe.
 Another way is useing a junk electronic keyboard for source, with a key taped down for continuous output.

[petemoore]

Are the input/output jacks soldered into the PCB ?
 This is a good source for problems to occur, some models are built this way, FWIU.
 If you have a DMM, you can check many debugging items mentioned, including voltage and continuity readings that may narrow the problem down quickly.
 Don't try this with lethal voltage potential items like amps, but plug the unit in an amp, start with the output jack tip, and see if you get a buzz sound when you connect your thumb to it [sounds like finger touching tip of live cable], then trace through the signal path of the circuit toward input and see where the sound buzz sound gets lost.
 You could plug a cable in a guitar, have someone strum the guitar, connect the sleeve [other end of cable] of the plug to ground, and the tip, with the signal in it, use that to start from output toward input as alternate source, as it should sound louder than the thumbuzz technique, does the same thing, [better for small Si Amps to use the guitar YMMV],
instead of a piece of wire touching your thumb and the circuit points, you need a strummed guitar, a cable, a test clip and a test clip/wire/probe.
 Another way is useing a junk electronic keyboard for source, with a key taped down for continuous output.
 It probably has the input jack wired to cut battery power, plug a mono 1/4 cable in to power it up for circuit testing.

[raf]

HI there

I have a problem with my wah (gcb95) that when it is on, there is no sound at all. No wah no guitar, nothing.

I have measrued the resistance across the 33K resistor (in mine there is a 67K). The seult is 20ohms . Is this ok or is the inductor bad?

[SnooP_Wiggles]

sounds fine to me. i measured  20-30ohm (can't remember exactly) when i was fixing a broken dunlop wah.

[raf]

Any ideas what the problem could be.

Problem: When wah is switch on, no signal is passing through, no sound.

I have put a new DPDT switch in. True bypassed.
The inductor is fine as it measures 20ohms across the 33K resistor.

Could it be a broken pot? I will measure the resistance later in the pot, But i am sure i did measure it yesterday and it was ok.

Any ideas please let me know.

[zachary vex]

the first thing i do when... aww, heck, i hate the word troubleshooting.  the first thing i do when starting failure analysis is to put a current meter (mA) between the battery and clip... i pull the battery clip off halfway and just leave one side connected, and put the mA meter inbetween the other two contacts and look to see what the pedal is drawing.  most pedals draw between 1 mA and 40 mA.  if it's not drawing anything, the first thing to check is the battery clip wires, and the next thing to check is the ring connection on the input jack to make sure it's clean and touching the MONO plug so as to short the black wire on the battery clip to ground.

actually, the first thing to check is the battery.  8^)

[raf]

Thanks Zachery for the info as I know you are extremely busy.
I will try it when I get home. I will let you know how I get on.

Thanks again

[raf]

I tested the current in the circuit which reads 3mA

I think it is time to make an audio prob.

[raf]

just made an audio prob.

I have checked the circuit and i dont thing there is anything wrong.

How are you suppose to use an audio prob correctly?

[raf]

just made an audio prob.

I have checked the circuit and i dont thing there is anything wrong.

How are you suppose to use an audio prob correctly?

[raf]

I have just plugged the wah in instead of using a battery and it is working.

I have clipped the battery in and measured the red and black leads from the battery and the reading is 7.5 volts.

Why doesn the wah work with the battery ?

Any ideas?

[Ed G.]

It is probably not working because the 9V adapter jack has an internal switch that breaks contact with the battery when the adapter is plugged in. If this switch is stuck, it will only let the pedal work with the ac adapter.
This happened before for me with the Dunlop-made MXR dyna comp.
You can either replace the switch or wire a jumper to bypass the adapter.

[raf]

Cheers Ed

I just tested the 9v battery by measuring the voltage to the board, which was fine and then i followed the trace, and the power stopped after the first 9v adapter jack lug (no power registered on the second lug).

For now I will use the adapter and when I pass the elec shop I will pick up a new 9v jack.