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Reparing my Citation 12

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  • Sydney
    replied
    How did you test the transistors?
    The schematic has voltage test points - did you test these?
    Yes bias pots are available.

    Leave a comment:


  • lasse
    started a topic Reparing my Citation 12

    Reparing my Citation 12

    Hi,

    I posted the beginning of this story...

    http://techtalk.parts-express.com/fo...ion-12-failure

    ...in this thread and I could really use some advice on where to go from here

    I finally came around last night to investigate which transistors is failing and other symptoms of failure:

    See the attached Pictures:
    -One driver and one pre-driver seems to be blown after diod-testing in situ but with the PCB removed
    -The Power-transistors are OK
    -The bad channel has a 8V AC on the output, almost no DC offset
    -According to the mounting-instruction (Yes, this was a kit in the 70ies!!), the heatsink is attached to the drivers (see pic nr 2)

    Now;
    -Is AC on the output logical if the indicated transistors are blown?
    -Are there modern replacement transistors?
    -Should both drivers be replaced in this situation?
    -I Think that the BIAS-trimpot caused this trouble in the first Place, is there good replacements?

    Any advice from you electronicians (is this really a Word) would help.

    Best regards//lasse
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