Pioneer SX-680 problem

Discussion in 'Pioneer Audio' started by RS Steve, Aug 8, 2017.

  1. RS Steve

    RS Steve Tube Junkie Subscriber

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    My brother sent this unit to me to have repaired, but I wanted to see if it might be something simple before taking it to my tech. Looks like this model doesn't have adjustments for the amp section though.

    My brother says after playing for over 15 minutes, it sounds like someone turns the volume down 50%. He has fiddled with the switches to see if they were causing it, but he says it has no effect. Seems to be heat related, and in both channels.

    I just wanted to see if anyone might have an idea what would cause this.
     
  2. JHS2RT

    JHS2RT and Miss Sasha Subscriber

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    Well --I'm sure you thought of de oxing all switches--they are notoris for causing drop outs. Sometimes playing with them does not help.
     
  3. RS Steve

    RS Steve Tube Junkie Subscriber

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    I walked him through doing a good deox but he said it still did the same thing. I just did another deox and have it playing to see if I can make it act up. So far no issues.
     
  4. ringading

    ringading AK Subscriber Subscriber

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    Sounds like perhaps a transistor is overheating and starting to fail. If you are up to it start with the output transistors and then work your way back to the drivers to test all of the transistors.

    I hope the Deoxit treatment did the trick!
     
  5. JHS2RT

    JHS2RT and Miss Sasha Subscriber

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    How's it doing?
     
  6. zebulon1

    zebulon1 Back repairing the PL's Subscriber

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    Both channels? If the Deoxit fails to help then look at the power supply.
    Check the voltages when the set is in the low volume mode.
     
  7. RS Steve

    RS Steve Tube Junkie Subscriber

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    I did a thorough deox and played it for a good 1-1/2 hours at a pretty loud output, no volume drop was noticed. I think my brother didn't get any deox into the push button switches, looks like all is well. :thumbsup:
     
  8. zebulon1

    zebulon1 Back repairing the PL's Subscriber

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    Those switches are difficult to Deox. Taking them apart to clean is not worth the extra effort. The best thing is several Deoxit treatments and checking for low resistance across the switches with your meter.
     
  9. larryderouin

    larryderouin Do I get Food, Med's, or more gear this Month? Subscriber

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    Very carefully, (and I DO MEAN VERY CAREFULLY) R&I the STK modules and replace the dried out heatsink grease, this will help cool down the modules. Look for dry solder joints around the power supply area of the board, and the power regulators. Adding small heatsinks to the regulators will shed a lot of the heat that migrates down the legs (all TO 220). A lot of the preventative measures for 780's should also apply to the 680. Be advised that if you do add heatsinks to the TO-220's use mica insulators, heatsink grease and nylon screws/nuts. The back of the transistor is electrically live (Base connection) which is why the insulators. You don't want to be probing with your fingers in that area with live heat-sinks. Sometimes the regulators heat up the legs so hot that the solder starts flowing off the connection. Same with the Larger diodes in the Power supply. It's not common, but does happen (diodes heating the solder).

    Now would be a good time for some preventive maintenance.
     
  10. zebulon1

    zebulon1 Back repairing the PL's Subscriber

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    Good point Larry :thumbsup:
     

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