Proco Rat 2 - Weak volume! - Solved

[Boksholm]

EDIT: Problem solved. It was a broken footswitch!

Hi!
I have a Proco Rat 2 (one with the old power socket). Everything works well but it's has very weak volume, even with vol+dist. on max it's lowers the volume compared to when it's bypassed!

The same problem occurs with both battery and ext, power supply.

Where do I begin? I have a simple multimeter but not alot of experience!

Kind regards!
/Filip

 

[BuddytheReow]

You could start by sharing some pics of the inside of the pedal. Both front and back. My guess is there is a weak connection somewhere

 

[Boksholm]

Of course! Before taking photos I installed the small jumper from one of the pots that can be seen, that was the only connection that looked a bit shady to me, but it didn't work!

Photos:

4 new items by Filip Böksholm

photos.app.goo.gl

Also attached!

 

[Sturdag Lagernathy]

Is that an original footswitch?
IME, a RAT usually fails op amp first, at least if it has a few years on it. We would need voltages.

 

[gonzo]

Not the original switch in there. That would be my first guess.

 

[Boksholm]

Sturdag: I see, I'm not really sure which components to measure and where!

Gonzo: Ok, I could just switch it, but I would install it the same way, would you guess that the switch is faulty (can volume loss be caused by bad switch?) or that it's installed the wrong way!

Thanks for your answers! =)

 

[gonzo]

Sturdag: I see, I'm not really sure which components to measure and where!

Gonzo: Ok, I could just switch it, but I would install it the same way, would you guess that the switch is faulty (can volume loss be caused by bad switch?) or that it's installed the wrong way!

Thanks for your answers! =)

Could be both. I would check the wires going to the board to the switch first before pulling anything. Bypass the switch with alligator clips if possible or an audio prob. Also check if the switch wiring is correct.

 

[Flying]

It's probably nothing, but just check this trace:

 

[Sturdag Lagernathy]

In 30 years, I've repaired maybe 10 odd RAT 2 pedals, probably 7 of those had a faulty op amp. Seems all would be OP07. The boards are fairly robust, but I do remember one had some liquid damage, and was de- laminating. Wires are very cheap feeling, but adequate. Your experience can vary, but voltages are a first step!

Put your black meter probe on ground. Touch each pin on the IC chip starting to the left of the "dot" on top. Thats pin "1". Go counter clockwise, down, then up the other side. Give voltages of each pin, 1-8. Set meter for DC, <20v.

Edit: That open trace is worth investigating, good catch Flying!

 

[Boksholm]

Flying: That was just some dirt, but yeah, good catch! =)
Sturdag:
1: 8,4
2: 4,2
3: 2,0
4: 0
5: 0 (This one is the leg furthest from the dot)
6: 4,2
7: 8,5
8: 8,4

 

[Guilherme Collateral]

I would check the JFET, then the Opamp, then the footswitch

 

[Sturdag Lagernathy]

Ok back to it!
Those voltages look good at a cursory glance, and Guilherme is right, JFET next!
Flat side facing you, left to right, pins 1,2,3 voltages please.
Is it a 2n5458?
Edit: just realized we're in general. We should probably move this to troubleshooting..

 

[Boksholm]

=)!

1. 8,53
2. 2,81
3. 0

I can't read what it says on the transistor because a cap is in the way!

 

[Boksholm]

Bump on the readings from the JFET! =)

 

[BuddytheReow]

Your JFET voltages look ok if the pinout is indeed DSG.

 

[Sturdag Lagernathy]

Can you get some resistance readings on the pots,( mainly just a continuity measurement, but if the resistance is odd speak up) [back in the day a fat slob slamdancing on my pedalboard comes to mind]) maybe a bad pot. Check continuity on that FS as well, it's been eyeing me funny. If not either of those..

And now, what you all have been waiting on: Audio Probe Time!

 

[Feral Feline]

Can this thread be moved to the Troubleshooting sub-forum?

 

[andrewsrea]

If this is a vintage era RAT, weak volume was part of the design. Some folks remove the 10K resistor which parallels the 100K volume pot to ground. The purpose of that leak resistor is to change the taper of the pot and leak off a lot of the signal. Removing it should provide a few more dB.

 

[Sturdag Lagernathy]

From the pics, its probably less than 20 yrs old. (Dammit ) it should have plenty of volume.
Edit: I see from the pcb it's a RAT 3 Rev. B..

 

[jimilee]

Audio probe?