Bridge rectifier intermittent.

Discussion in 'The Projects Forum' started by zklrds, Jan 17, 2015.

  1. zklrds

    Thread Starter New Member

    Jan 17, 2015
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    I have a bridge rectifier that passes the diode test with my multimeter outside of the circuit, but when I solder it back into its place on the de-energized PCB, the AC pins read current across them. Also, when soldered (or gently held in its place, I tried) any test with any pair of pins yields a bias current reading instead of OL when incorrectly biased. I've tried with two different W02M bridge rectifiers that test well outside of the circuit. I'm losing my mind.
    Btw, this is a logic board power supply for a 1989 Nakamichi TA-4. If necessary, I'll post the schematic. Thanks for any advice.
     
  2. crutschow

    Expert

    Mar 14, 2008
    13,056
    3,245
    I'm afraid we need the schematic. ;)
     
  3. zklrds

    Thread Starter New Member

    Jan 17, 2015
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    0
    crutschow.
    Thanks for responding. Here's a link to the pdf in my dropbox.
    https://www.dropbox.com/s/wbg00j90pktszgk/Nakamichi_TA-4_service_manual.pdf?dl=0

    The bridge rectifier in discussion is D956 on the video & logic PCB. pg 42.

    This is where my troubleshooting skills have led me, at least. I could be way off.:confused:
    The overall problem that I'm having with the unit is that occasionally the display, tuner, and volume will suddenly shut down, typically with a loud click. The unit will still be on, as indicated by the power LED and remote functionality for the input selection, but there'll be no sound or radio. This will last for a few weeks, sometimes a few months, before I randomly turn it on to check it and it the unit somehow works again.

    A note: though the input selection on the front panel works (LEDs light as you press each button) the display above it (for the tuner, speaker selection indicator) is dead. Also, the 3V lithium battery on the logic board that I assume is for the tuner memory is only reading .8V. Maybe that helps.

    Fingers crossed.
     
  4. zklrds

    Thread Starter New Member

    Jan 17, 2015
    4
    0
    Removed the bridge rectifier from the board and I'm getting the same readings from the contacts at its vacant position. So...it's not the rectifier, at least. Any guidance?
     
  5. zklrds

    Thread Starter New Member

    Jan 17, 2015
    4
    0
    Turned out to be a loose connection on U501. After removing basically every component from the board, I found it.

    Thanks for reading.

    Also, if you need your Nakamichi TA-4 fixed, I'm your person.
     
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