Diagnosing a broken ProCo Rat.

[Dolmetscher007]

I have been putting off posting this message, because I am not extremely knowledgeable about PCBs and schematics. I know how brutal online forums can be when someone asks a question that is really difficult to answer in this format, especially when the OP (me) has a tough time keeping up with the tech.

Here goes nothing...

I have a Pro Co. Rat that I bought new in circa 2005. I am not sure which version of the RAT pedal it is. The PCB inside (photos attached) says PRO CO SOUND INC. RAT 3 REV B. I did a lot of reading online about the history of this pedal, starting in 1978, and I know there were a lot of Rat off shoots, like the "Dirty Rat" and the "Turbo Rat". I guess mine is a Rat 3, but it only says that on the PCB. The outer case is the black heavy gauge steel and just says RAT on it. No, "Rat 2" or "Rat 3" So... ()

Anyway... I do not have a 9V power supply with the mini jack connector the RAT uses. I do have a box of brand new 9V batteries, and I've put in several of them to make sure it wasn't just a dead battery issue. What's happening is, the pedal just appears to be dead. When I plug my guitar into the input jack, the red LED does switch on and off as I click the footswitch, however, there is simply no sound. The problem is also not my cables. I tried it with several cables, and I even used my multi-meter in continuity mode to test each cable to make sure it beeps when I touch the leads to each 1/4" jack.

I tried to look at the schematic online for the Rat, but... I guess I never really realized how different a schematic is from a detailed wiring diagram. None of the RAT schematics I could find online even show that there is a footswitch involved. I could be wrong, and just not seeing it right in front of my face, but it looks like the schematics just show the input, the 9V in, and the output... with a lot of resistors, capacitor, and an IC in between.

Can any of you guys point me in the right direction on where to even start as far as trying to diagnose what's wrong? I have a really nice multi-meter, but I'm not sure where or how to start.

[GGBB]

You have a USA made RAT2.

RAT schematic:


The switching should be similar to FS1 (purple - ignore FS2 green) in the drawing but the LED is a separate pole of the switch not related to the circuit switching.

It sounds like the IC might be dead, but that's just a guess - might be the switch or the FET. Can you post the voltage readings explained here: https://www.diystompboxes.com/smfforum/index.php?topic=29816.0?

[Dolmetscher007]

Wow!!! This is awesome @GGBB! Thanks man. I will get on this right now!

[Bandwagonesque]

hello. i'm rather green too but hope I can help. I don't seeeee anything wrong. nothing broken loose or burnt. you may want to check continuity now between your leads from the board to jacks and switches just to be sure. If all beeps like it looks like it should (I see no loose anything. C7 looks weird but it looks like its going through where it needs to), then you'll likely have to provide your readings for each pin on the IC (the chip) to help us help ya. Set your meter to voltage, park your black probe to ground on the circuit (see that green wire, measure off that) and then probe each leg of the chip with the red end. I hope this helps and hope i'm right. I fixed my broken rat last year and it was obviously the IC. Pulled it and replaced it and good as new. I reckon if that's your problem. If I wasn't out the door id find you some correct voltages to base off of but would be happy to get that in a bit if you can't track them down through here on your lonesome.

[willienillie]

I would add a little solder at lug 3 of the distortion pot, just for good measure.

[iainpunk]

in this case, i STRONGLY recommend building an audio probe:


the audio probe clips to ground and has a cable to your amplifier and then the probe is there to check if there is any audio signal in different points in the circuit. this allows you to follow the path of the audio through the circuit and find where it stops. that generally gives you a perfect indication where somethings wrong.

(in regards to your ''fear'' of posting here, this forum is very unlike other forums.
95% of the time, we are all nice, polite and helpful, even though this goes against the 'internet laws of physics' (we have little to no moderation on this forum, were just nice here)
[an unmoderated (censorship free) place becomes right wing over time, a moderated place (WITH sensorship) becomes left wing over time {unmoderated and right wing: 4chan // heavily moderated and left wing: Reddit/Facebook}])

cheers, Iain

[drummer4gc]

Do you get any sound in bypass?

[Radical CJ]

in this case, i STRONGLY recommend building an audio probe:

+1

In my (limited) experience identifies problems faster than a multimeter in most cases. Probably not a good idea to randomly poke one into a live 100w amp your trying to fix unless you know what you're doing, but into a 9v pedal is safe.