So I was asked to fix a Morley steve vai bad horsie wah for my first guitar teacher. He is a great guy so I want to figure this out.
Apparently a beer got spilled on the wah pedal and now it no longer works properly. I plugged it all in and it sounds as it should but the wah is always on. The effect does not turn off. For those not familiar, these wahs are turned on and when you put your foot on the pedal. I took a look under the hood and everything 'looks' normal.
My question is where to start. I think something must have shorted out when liquid got in there. I know I am looking for the switching part of the circuit. Am I right to think it could be some transistors that are controlling the on/off.
Any advice would be helpful.
There are 2 pairs LED/LDR. One pair detects when the pedal has moved slightly from the "at rest" position, and turns the effect on, at pin 13 of the CD4069.
I had an original Steve Vai Bad Horsie wah about 10 years ago. As I recall, there is a trim pot adjustment that controls the sensitivity of when the effect turns on/off. Have you checked this?
Didn't really care for that pedal because I could never adjust the off to on delay to disappear. It always took a second for the effect to engage when I pushed the pedal.
This may help too... scheme:
http://www.morleypedals.com/vai-1es.pdf
As Ian says: find the LED and LDR which is blocked by a light-blocker when pedal should be "off". From the symptoms, it does not see the light. Does LED light? Check for thick beer/dust crust or loose junk blocking the light. Check for pivot bent so that light-blocker is not blocking/un-blocking light.
Tack a 470 ohm resistor across the LDR terminals. If the pedal now goes "off", replace the LDR (exact type not very fussy).
Still stuck "on"? Examine the area from LDR to the two JFETs. Heavy damp beer-spill may leak enough to drag down voltages.
(http://i.imgur.com/YspOS.gif)
Old beer might be cleaned with very pure water with a drop of alcohol (drugstore or strong vodka), a swab, and then WELL-dried. Neglected beer is liable to have corroded leads, joints, traces: this may become a "mechanical" repair like patching old car floorboards.
> I could never adjust the off to on delay to disappear
The on-to-off delay is set by the 4.7uFd and the 330K or 1Meg+47K resistor.
The off-to-on delay is the 4.7uFd against the U1 CMOS output. I calculate this as less than 0.002 seconds. +Plus+ the 1Meg against the 0.047uFd over nearer the JFETs, which is 0.05 seconds. That's pretty quick. If you must have snap-off, try 100K or maybe 22K at R8 R9. But down in that range you risk a "click/pop".
I realize that this is an old post. But is it possible that this pedal could get stuck in the "off" position? I've got power to the pedal, but only one set of LDR's is lit up, (main ldr on lightblocker). The second LED is not lit, (at top of lightblocker). Should I replace LED? When I activate pedal, LED on face of pedal doesn't come on and there is no Wah effect. Signal goes through pedal, but no effect when pedal is stepped on. I've checked a few voltages based on the schematic in this post, everything seems ok.
LEDs rarely fail. I'd look for bad solder, then other bad parts.
Voltages at both ends of both LEDs would narrow it down.
I know this thread is quite old... But I have the same problem with a Bad Horsie. It refuses to turn off. sgmezei, did you ever fix the problem?
PRR, I tried what you said. I held a 470 resistor to the LDR terminal that, if I understand correctly, controls the on-off. The LDR1. It didn't turn off.
Is someone able to help me with this? I would greatly appreciate it!!
Thanks!
Welcome!
> I held a 470 resistor to the LDR
me> Voltages .... would narrow it down. (http://www.diystompboxes.com/smfforum/index.php?topic=94640.msg816864#msg816864)