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Need help T-shooting a fender SS

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  • Need help T-shooting a fender SS

    This is a "FM65", and I uploaded the schematic here...
    FM65.pdf

    The issue is with the 5v supply. I replaced everything in it including the rectifier, all 5 caps, and the 7805 regulator. Sill i only get under a volt at output of the rectifier which should be 11vdc. Then i cut the trace at the output of the rectifier and it goes up to the correct 11vdc. So something is pulling it down, but apparently not in the supply since i already replaced it all. I guess the next step would be lift the first component in every place of the circuit that draws from the 5v supply and see where exactly it's being pulled down. But i'm at the end of my rope and this amp is a real drag to work on. So i was hoping someone could tell me what the most likely place to look is, assuming there IS one. I'm not very good at circuit theory so what might be very obvious to some of you like Enzo is greek to me. Thanks for any help.

    Edit: oh, and i also replaced Q1 and checked the immediate parts there.

  • #2
    You've already figured out the next step, you have to find out what is pulling down the 5 volt supply. The 5 volt supply only goes to a few places, the channel led at Q1, ICs U5 and U6 and the DSP logic board.

    The easiest to check would probably be the DSP board. Pull the plug on it and see if the 5 volts comes back. Do either U5 or U6 get hot?

    Have you checked for bridged traces around the 7805 or the replaced caps?

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    • #3
      No bridged traces, and if i pull the DSP plug it goes up a bit but only maybe a volt or less. U5 &6....didn't check for heat but i will when i get back to it. since i posted this i've replaced a ton of parts even tho i had no reason to suspect them other than being in the line of fire. This is really a tough one. Thanks for looking, i appriciate it.

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