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Newbie requesting help with a dead ProCo Vintage Rat

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  • #16
    Originally posted by The Dude View Post
    Normal pedal architecture has the ground path completed when a plug is inserted into the input jack. You do have a plug there for testing?
    Yes, good point!

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    • #17
      Originally posted by Dave H View Post
      It’s most likely because pin 4 is open circuit from ground/battery negative. With the battery disconnected check for continuity between battery clip -ve and pin 4. If it isn’t a very low resistance find out where the open circuit is and correct it then do as Juan said and check the DC voltages on the op amp pins wrt battery -ve. They should read 4.5V on pins 2,3 and 6. 9V on pin 7 and 0V on pin 4.
      This was instructive - there is an open circuit there. Didn't get far figuring out exactly where last night - maybe one of the capacitors just up from pin 4 is fried but not sure yet.

      This is great though - I have something to go on now. Thank

      The Dude: I did have a plug in the input jack, but worth pointing out!

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      • #18
        Maybe this will help- schematic with notes/changes for the various Rat pedals.

        https://music-electronics-forum.com/...6&d=1387061571
        "I took a photo of my ohm meter... It didn't help." Enzo 8/20/22

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        • #19
          Thanks The Dude - I found that very helpful indeed. That covers my circuit.

          Managed to get distorted but quite crap sounding audio out of it after connecting pin 4 direct to a known-good ground point. Investigating now where the open is between 4 and the point its connected to in the actual circuit, which is the DPDT switch. I have a feeling the switch is bad so the chip might not be the only thing that isn't grounded.

          I'm tempted at this point to make a clone of an LM308 rat and use my existing pots, jacks, and housing. Whatever it is that's broken will be fiddly.

          Thanks all for the help.

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