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Thread: Technics SC CA1080 Hifi amp

  1. #1
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    Technics SC CA1080 Hifi amp

    Hello
    Im hoping somebody can help me I have a Technics SC CA1080 hifi midi system in
    Iv'e had these before, Normally a dj or two on the output chip,
    This one had the same found a few djs , soldered them back up, and tested found still no sound. Headphone working ok as this comes from another chip

    Found i had correct supply voltage and see audio in on the scope and can see nothing at the outputs

    Replaced the chip ( IC501 RSN3403 and still the same.
    Signal is present at the inputs
    technics_se-ca1080.pdf
    all the voltages at the chip are present and correct apart from
    Pin 7= 0v
    Pin 12= 0v at collector junction with
    The chip i got new from ebay and UK firm had it shipped from china i have used them before but never for this item

    Anybody have any idea's

    Have a good Day

    BBB

    Forget the link below i attached the wrong one !!
    Attached Files Attached Files

  2. #2
    Senior Member Enzo's Avatar
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    Disk Jockey?

    What is a dj?

    Q201,202 are muting transistors at the PA input. Are they turned on?
    Education is what you're left with after you have forgotten what you have learned.

  3. #3
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    Dj = dry joint I have finished for the day now I will check tomorrow. Thanks enzo

  4. #4
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    I have finally got round to checking it again . I think myself the chip is faulty. Ebay seller ive used before has been good but has got some bad feedback for fault or cheap parts.
    Pin 12 on schematic says its should have 12V- but has 0v
    Pin 4 say it should have 4.5v- on but has zero

    These chips are hard to find either get from the usa or china


    pin out voltages are

    Pin 1 0v
    Pin 2 36v+
    Pin 3 36v-
    Pin 4 0v
    Pin 5 14v-
    Pin 6 0v
    Pin 7 0v
    Pin 8 14v-
    Pin 9 0v
    Pin 10 0v
    Pin 11 signal good
    Pin 12 0v
    Pin 13 signal good ( seen on scope )
    Pin 14 0v

    Does anyone have any thoughts on using a different type of power output chip and wiring in. Any unforeseen issues

    BBB

  5. #5
    Supporting Member Jazz P Bass's Avatar
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    Not too sure about pin 12 supposed to having -12.5v on it.
    It's the 'sync' pin.
    Usually it's grounded.

    Pin #7 is a problem.
    That is the 'mute' pin.
    Unfortunately the voltage is supplied internally.
    I would try replacing the cap on that pin.

  6. #6
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    I have changed the cap if my memory serves me right. Not in the workshop now. Will check tomorrow

  7. #7
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    As i thought i had changed the cap on that mute pin. 7. I did note that it was internal voltage when i checked it, so as it was a 0v i put 2+ 2 together and thought chips up the spout

    Ive rigged up a -4v on the the mute and the whole thing seems to work ok. just running it on test.

    BBB

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