Guyatone PS104 Cross Over Box Auto Wah - PLEASE HELP!!!

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Guyatone PS104 Cross Over Box Auto Wah - PLEASE HELP!!!

Postby celestinocamicia » 24 Dec 2011, 01:36

Hello everyone!
A couple of years ago, I visited a small shop back in my native Italy which primarily sells CDs, music-related clothes and gadgets, but they also had a few instruments and some NOS 70s and 80s effects, mics and other stuff.
Amongst them was a Guyatone Cross Over Box Auto Wah, which I decided to buy as I knew the "Box" series pedals are quite collectable, but as soon as I got home and plugged it in, I got some really bad news as it didn't work properly, but instead of asking for a refund I decided to keep it anyway so that I could try and repair it in the future, and have a nice vintage effect that also works.
Fast forward to 2011, and I finally decided I want to bring that old brown box back to life; it will be reaching me (I'm currently in the UK) in a very short while.
Now, here are the faults: when I put the battery in and plug the guitar and amp into the respective sockets, the LED stays on even when the effect is not engaged, but it appears not to be a fault as I saw a video in YT of a working example doing the same, and when I switch it on, instead of the proper envelope filter I get notes swelling up when I pick them, à la Slow Gear, introduced by a sort of "spitting" noise, and the controls affect the length of this weird swell as opposed to controlling the sensitivity and depth of the wah sweep.
Now, here is a schematic I found on the web: Image
It says "Vox 1904" but it is the same circuit as the Cross Over which was put into a different case and sold as a Vox pedal at the time.
And here are pictures of the circuit board of the Vox version: front Image and back Image
As you can see, there's a big green capacitor slap bang in the middle of the board, just below the op-amp...well, that capacitor is missing from my pedal!
Could that be the cause of it not working? If so, which value should it be? I'm not much of an electronics expert, I'm not able to locate it in the schematic :-(
Could it be, instead, that the op-amp might be shot? Just in case, I got hold of a new LM1458N...shouldn't that be the case, it would still be a good thing to give it a fresh IC. :-D
Sorry 'bout the lengthy message and newbie content, but I want to fix this old pedal for good and I'm sure you will help me solve its problems :-) Thanks!
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