MXR Bummer

[humanbn]

My MXR distortion quit working. It's an early 70's model and I'm upset. I don't know what's up. When it's off my guitar signal still travels to the amp but when on there's nothing. New battery and everything. Tested all the components and the wires and all carry a current. No shorts in the circuit. What went wrong? If a cap would have worn out there would still be at least a little signal going through, right? If I remove the battery while the pedal is plugged in, even if it's on and there's no signal from the guitar going to the amp, there will be a pop in the speaker.

[ashcatlt]

I posted this in another thread, but it's exactly what I wanted to reply to this thread as well, so here you go:

Got an audio probe? If not, make one. All you need is a guitar cable you can afford to cut up and a capacitor (preferable non-polarized, but value isn't particularly important). Some aligator clips can make things easier. Remove one end of the cable. Twist the braided shield together and connect it to a convenient ground point, like the ground lug of the output jack from the pedal. Twist the central conductor of the cable and solder to it one end of the capacitor. Plug the intact end of the cable into an amplifier or other monitoring device.

Now you can touch around inside the pedal with the free end of the capacitor and hear what's happening at any point in the circuit. The capacitor is there to block any DC voltage from being passed on into the amplifier.

In your case you'll be poking around to find where the signal ends. You should find that on one side of some component there is sound, and on the other side there is nothing.

You will need to feed the input a recognizable signal, of course. I often use a synth in arp+hold mode, but you could use a cd player, have your friend strum the guitar, or whatever.

[humanbn]

Thanks for the help. I do have a question, however. About the cap being non-polarized, if I only have a polarized one which end do I connect to the cable? Does it even matter?

[ashcatlt]

I wouldn't use a polarized cap for this. I've never tried it, but I'd expect it to give inconsistent results at best.

You can, apparently, wire 2 x polarized caps in parallel (pointing opposite directions) to simulate an NP. Just remember that capacitance adds in parallel (unlike resistors).

The value isn't crucial, but shouldn't be too high, or it won't pass much in the way of audio frequencies. This link recomends .1uF. The forums on that site are a great resource for, like, DIY stompboxes...

Caps are cheap, buy a couple.

[humanbn]

I checked the circuit and it seems that the IC chip has gone bad. Any ideas as to where I can get a vintage replacement? I will settle for a new one if I have to but I would like to keep my pedal somewhat original.

[flateric]

Try www.vintage-parts.com in London, they may be abole to help you.