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Sansui 6060 Rehab. Please Help if Possible

Discussion in 'Exclusively Sansui' started by W.T. Holt, Jun 14, 2016.

  1. W.T. Holt

    W.T. Holt Member

    Messages:
    79
    I recently acquired a 6060. The unit didn't power on, but it cost me nothing so I figured I take it... why not. Upon opening the case, two fuses on the the power amp board (which are also directly connected to a pair of secondaries from the transformer) were blown (f602 and f603). First move - replace the fuses and retry powering on... they instantly blew.

    I am fairly new to audio repair but have seen a similar issue in a Pioneer receiver... replacing the output transistors took care of that problem, but replacing the outputs (and associated resistors for good measure) in this amp have not solved the problem.

    When the power switch is on and the blown fuses are still in the board, a specific resistor (r612) gets extremely hot and starts to smoke... testing the resistor out of circuit shows it is still good though.

    I have not found any shorts on the board near the problem areas... but more testing could always be done

    So far here are my thoughts, and this is where I'd love some input on whether I'm on the right track or not. The fuses are blowing due to either too much power coming from the transformer/power supply (the secondaries put out around 26V not the specified 24.8V) or a short somewhere else on the board. The overheating resistor is somewhat of a mystery to me, but I have to imagine it is related to the issue with the fuses.

    Anyway, if you can glean any insight from this mess I've described I'd love to hear your thoughts. Any help in trouble shooting will be greatly appreciated!
     

     

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  2. Hyperion

    Hyperion Roobarb & Custard Subscriber

    Messages:
    48,022
    Location:
    Hertfordshire, UK
    It would appear you have a short circuit on the power amp side of R612 (as opposed to the bridge rectifier side). This resistor is getting hot very likely because of some issue with the output transistors. If you found any one of them damaged originally and replaced them, it is very likely driver transistor(s) will also be damaged or perhaps more likely the bias circuitry, TR05 // VR01 is damaged. For example, an open circuit bias trimmer will cause maximum bias to flow in the output transistors - which would cause this effect. Have you made yourself a DBT? - this will help with future diagnosis and component preservation, as you can usually take measurements with power applied.
     
    Last edited: Jun 14, 2016
  3. DougBrewster

    DougBrewster AK Subscriber Subscriber

    Messages:
    521
    R612 is the +ve supply to the driver board and is clearly handling excess current due to over-driven or shorted TR7/9 and TR8/10 (both F602 and F603 are blowing showing a fault on both channels) so I'd be taking a look at R601 and ZD 601 on F2647 which are common to L and R. Your new outputs may well be blown...
     
  4. W.T. Holt

    W.T. Holt Member

    Messages:
    79
    Ok interesting thanks! Will be looking into this soon and will report back
     
  5. rotco

    rotco Active Member

    Messages:
    157
    @W.T. Holt
    it's been along time...
    but, how this story ends?

    i have a quite similar issue.

    thanks
     

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