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Peavey JSX Switching Problem...Weird

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  • Peavey JSX Switching Problem...Weird

    Ok. Im a very experienced tech. thetonedoctor.net. Maybe I just need another set of eyes. Basically this is the JSX head. Started having a strange switching concern. Basically when you switch to ultra ch 3 via the front panel or footswitch...all is good. Same for crunch ch 2. However, when I switch to clean ch1 via the front panel or footswitch, the LED for the crunch channel 2 refuses to enter "off" state. Altho the audio path is indeed switching properly to clean sound..both the clean and crunch LED's stay lit. I cannot figure out why this ch 2 led will not turn off when in ch 1 clean mode. I already replaced all the switching fets. Have not changed any relays ... I have tested all 4148 diodes. They appear to be fine. Any thoughts?

  • #2
    What voltage do you read at LDSW in the 3 modes? ( cathodes of D24 and D22 )

    grtz,

    Strato56

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    • #3
      If all else REALLY works right, then follow the LED current, it comes through a transistor, and then,,,

      But if K3 works but K2 is stuck on, you might not realize it, so VERIFY each relay is pulling in and dropping out. Those relays are in series with the LED current.
      Education is what you're left with after you have forgotten what you have learned.

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      • #4
        Will report back with findings.

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        • #5
          And the other weird thing is..when I toggle between ch 2 and ch 3 ..the LEDs behave properly. Its just when I go to ch 1....that the ch 2 led refuses to turn off. Both 1 and 2 are lit up simultaneously. But like I said... when I go to ch 3....the ch 2 led DOES turn off as its supposed too. I just can't figure out the mechanism in ch 1 that is supposed to make the ch 2 LED turn off.

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          • #6
            Can we use part numbers? Like D4 is the green LED. I have no idea which LED is channel 1,2,or 3.

            Look at your circuit. It is more about what turns things on than what "turns them off".

            D4 is green, and is turned on and off by relay K1. Period. K1 is controlled by S1.

            K2 and K3 work with LEDs D24 and D22. The circuit is more or less a flip flop, in that one side inverts the other, so there can only be one of them on at a time.

            That is why I suggested earlier to verify the action of the relays.
            Education is what you're left with after you have forgotten what you have learned.

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            • #7
              It appeared to me as if the leds were feeding off the field circuit of the relays...not off of one of the actual switching contacts. Am I wrong?

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              • #8
                I believe the culprit is Q12

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                • #9
                  The switching relay contacts are all in the audio path. The relay coils are driven by transistors (K2,3), one transistor acting as an inverter so the other relay operates opposite the first.

                  Q12? Based upon what?

                  Please...tell...me...

                  What diode number is the LED that stays on? And can you please verify whether or not the relay coil circuits are energizing? You can't get at the relay coil terminals easily, but you can get at the diode in parallel with them, next to the relay. And you can get at the collectors of Q7, Q11, and resistors R91, R101.
                  Education is what you're left with after you have forgotten what you have learned.

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                  • #10
                    All 3 legs of q12 were open....not sure how it sustained damage. A common J174 fet.... Changed q12. All is well.

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