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Voltage supply to CD player issue...

Discussion in 'Audio' started by tom1970, Aug 23, 2021.

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  1. tom1970

    tom1970

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    Aug 23, 2021
    Hi everyone. I'm new here. Wondering if anyone can help.
    I'm trying to repair a Sony Micro Hi System...sony_hcd-bx77dbi
    The CD player is not spinning. Think both the sled and spindle motors are not turning. I believe this is due to the voltage supply to the CD unit coming off the main board. If you have a look at the attached pic (part of the main board) there should be 3.3V going into the pins 1 and 17 of the output ribbon which goes to the CD player. But I'm getting weird voltages from -2.6V to +1V at both. There is a little cluster of transistors (the 3.3V regulator circuit) - Q302 Q303, Q392, Q361 and the voltages are mostly wrong (in the pic the numbers in Red are Sony's correct readings, the numbers in green are mine).

    I thought it might be something to do with the zener diode (D304) so I swapped in a new one but still getting the same readings so could it be one or more of the 4 transistors - if so which one??? Q302's readings seem more or less correct but Q303's are just weird with the negative value on the collector. Any suggestions gratefully received...
    Cheers
    Tom
     

    Attached Files:

  2. Harald Kapp

    Harald Kapp Moderator Moderator

    11,702
    2,716
    Nov 17, 2011
    Check the electrolytic capacitors in the power supply. Look for leaking or bulging ones. Replacing those can often remedy power supply issues.
     
    tom1970 likes this.
  3. tom1970

    tom1970

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    0
    Aug 23, 2021
    Thanks for the advice. The caps seemed fine on inspection. Certainly the main power caps were ok because other DC voltage rails were good. - 7V, 9V etc. It was just these two 3.3V ones that were dodgy. I've actually given up on this thing now as I've spend more time than I should have on it. Thanks again for your help!
     
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