Solid State Bass Guitar Amp not Working

Discussion in 'General Electronics Chat' started by steve.pierce7, Jan 7, 2016.

  1. steve.pierce7

    Thread Starter New Member

    Jan 6, 2016
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    Good afternoon folks. I have a 60s National Valco solid state bass head that has 3 diodes that cannot be identified by the best repair guy in the area. I have absolutely no idea what the diodes are, the repair guy said they run with the output, and on the diodes are a 5, a T, and what looks like maybe an L or a 7. I was just wondering if anyone can help me out before I toss the thing for good. I've attached a couple of pictures of the diodes, and the bass amp circuit board, with arrows pointing to the locations of where the diodes should be.
    20160106_162837.jpg 20160106_163453.jpg 20160106_162825.jpg 20160106_162818.jpg 20160106_163447.jpg
     
  2. Lestraveled

    Well-Known Member

    May 19, 2014
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    It looks like a 1N4148. Is it bad??
     
  3. steve.pierce7

    Thread Starter New Member

    Jan 6, 2016
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    They're shorted out, so the repair guy couldn't get a reading. It's three of the diodes
     
  4. Lestraveled

    Well-Known Member

    May 19, 2014
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    OK, they look like 1N4148 diodes, which are rated at 1/4 amp. I suspect that other parts are bad that caused these diodes to fail. Have you tested (ohm meter) the D525 transistors??
     
  5. Lestraveled

    Well-Known Member

    May 19, 2014
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    Looking at the your pictures, the D525 transistors have been replaced before. Their true part number is really 2SD525. They might be bad.
     
  6. steve.pierce7

    Thread Starter New Member

    Jan 6, 2016
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    the repair guy had changed some of the bad parts, and said everything besides that was in good working order, I'll make sure he does a test once the diodes come in. Thank you so much for giving me a possible solution sir!!!!
     
  7. Lestraveled

    Well-Known Member

    May 19, 2014
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    Wait a minute, I didn't say they were 1N4148, they just look like them. Replace them with 1N4007 and forget about them.
     
  8. steve.pierce7

    Thread Starter New Member

    Jan 6, 2016
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    Ahhh, thank you so much!!!
     
  9. dl324

    Distinguished Member

    Mar 30, 2015
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    That's not saying much about his ability...

    Do you have a schematic so we have more to go on? Zeners are also common in that package, though not likely to be in the output.
     
  10. steve.pierce7

    Thread Starter New Member

    Jan 6, 2016
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    Unfortunately the schematic was so old the ink had chipped off virtually all it, so it was of no use to the guy I took it to.
     
  11. dl324

    Distinguished Member

    Mar 30, 2015
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    Any repair person would be able to trace the circuit and make a schematic. Are you able to do it for the circuitry around the diodes?
     
  12. Dodgydave

    AAC Fanatic!

    Jun 22, 2012
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    Its got a C on the diode body, it maybe a Zener...
     
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