Rat volume dies sporadically

[57champ]

I've got a rat type B that I want to mod, It's quite old and beat up but sounds great when it works. It randomly, and for long periods of time, cuts out and I can only hear a signal if I crank the volume and Distortion. I thought the sporadic issue was due to a bad transistor, but I replaced this and it didn't fix the issue. Any help would be appreciated, could the pots have gone bad with age and shorted to ground? Do I have a bad cap? I don't know where to go from here and I would like to avoid replacing every part in the thing.

[Earthscum]

To me, it sounds like possible caps. From reading around, it sounds like the older the electrolytic caps are, they are more prone to fail, and a bit more than just the obvious age. Manufacturing techniques got alot better over the years, and things get proportionately (or not) more reliable.

I would check wires, solder joints, and all the visual things first, and consider at least swapping out the 'lectros. Also, check to make sure none of the pots have spun enough to loosen a lug from the board, or touch another wire. Lots of Ratxperts around here, so someone may jump in with a more specific idea. GL!

Oh yeah... you may grab yourself a multimeter and read through this thread, as well. Take down your voltages, and you can either post them here, or get the thing to work in it's intermittent mode and quickly take voltages again and post the entire thing here. They would give a ton of clues as to what's going on with it.

[pedalgrinder]

i disagree that its caps i believe you have a high resistive joint there somewhere thats coming and going with certaing conditions. could be a crazy one to diagnose

[GGBB]

I had a tone cap go in one of my guitars once and it did the same sort of thing.  Not sure if that would apply to a RAT, but I'd agree with earthscum that electrolytics fail earlier than others, so in an old pedal with a problem they should be suspects.  Start with the 1uF output cap, then try the 4.7uF cap connected to the filter pot as those are the only two electrolytics in the signal path.  When you crank the volume and distortion is the sound as expected or are you just getting a weak signal?  If it's weak, you could jumper 1 and 3 on the pots to bypass them and rule them out.

[57champ]

Thanks, I will try and look into this. I have an odd feeling that it might be the pots, they're really old and hard to turn and I made the thing cut out by moving one. I'm going to try and bypass them and see what happens.

[pedalgrinder]

I found using inox it is a lubrication spray really good for getting old pots up and running.

[57champ]

Ok so just worked through some more and came across something interesting, one of the mods I wanted to do to the pedal was to put a switch in that bypasses the clipping diodes to get more of a overdrive pedal sound, I de-soldered the ground side of them and plugged the thing in just for kicks. What was interesting was that my volume was back, I know bypassing the diodes will increase the volume on a working pedal but the fact that it made mine go back to working volume makes me think the diodes might be bad, even though they tested ok when I disconnected them. I'm quite confused, I don't know what other factors could be playing into this.

[57champ]

never mind that last comment, If I push down on the pots while its upside down the thing works fine, bad pots I think. Smallbear here I come.