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1979 Fender Twin Reverb - can't turn off reverb

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  • #1

    1979 Fender Twin Reverb - can't turn off reverb

    I have a '79 Fender Twin Reverb Silverface that worked fine for couple of months, a few days ago, I noticed that I can't turn the reverb off with the footswitch. I've checked the footswitch and it's ok. Please help, THanks.
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  • #2
    Does the reverb shut off when you unplug the footswitch?

    How did you verify proper operation of the footswitch?

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    • #3
      The reverb doesn't shut off when I unplug the footswitch. The vibrato side is working so I switch the plug and the vibrato is still working, also I test the footswitch with a multi-meter and they're all function properly. Thanks.

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      • #4
        135 watt twin right? The reverb on/off is a simple circuit. The foot pedal basically grounds the grid of the recovery tube. Without the foot pedal the reverb would be on. If the foot pedal is making, then there must be a bad connection between the recovery grid terminal and the jack pin. I assume you can eliminate the reverb by turning it's control fully CCW right?
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        Warning! Some Electronics devices contain lethal voltages that can kill you. If you do not feel qualified to work with dangerous voltages, refer your repairs to a qualified technician. By giving you online advice, I am assuming no liability for any injury or damages you might incur through your own actions.

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        • #5
          Yes, it's 135w twin. And I can eliminate the reverb by turning the reverb knob fully CCW. THanks much.


          Originally posted by bnwitt View Post
          135 watt twin right? The reverb on/off is a simple circuit. The foot pedal basically grounds the grid of the recovery tube. Without the foot pedal the reverb would be on. If the foot pedal is making, then there must be a bad connection between the recovery grid terminal and the jack pin. I assume you can eliminate the reverb by turning it's control fully CCW right?

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          • #6
            I posted on this a while ago, I must have hit the wrong button.

            When you ohmed out yoour stomp switch, did you measure it right at the switch terminals? What you need to do is go to the plug end of the footswitch cord - the shielded one, and measure resistance from the plug tip- to the outer contacts. Does it still off/on when the sdwitch is pushed? If not the wire connections are broken somewhere.
            Education is what you're left with after you have forgotten what you have learned.

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            • #7
              Originally posted by bnwitt View Post
              135 watt twin right? The reverb on/off is a simple circuit. The foot pedal basically grounds the grid of the recovery tube. Without the foot pedal the reverb would be on. If the foot pedal is making, then there must be a bad connection between the recovery grid terminal and the jack pin. I assume you can eliminate the reverb by turning it's control fully CCW right?
              Having this info... make a shorting plug with an RCA connector or an RCA cable that you can sacrifice.

              Plug it in and see if there is a change of state. After all you are looking to isolate where the problem lies.

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              • #8
                Problem solved, found a bad connection between the recovery grid terminal and the jack pin as bnwitt described. Thanks much.

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