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G5 Mac Power Supply Relay

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    #41
    Re: G5 Mac Power Supply Relay

    We appreciate follow-up posts though.

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      #42
      Re: G5 Mac Power Supply Relay

      Originally posted by Toasty View Post
      I want to check the output MOSFETs for shorts.

      Unit unplugged from mains.
      Black probe to the common output ground, black wire bunch as before.
      Check each of the 3 output lines (3.3v orange, 5v red, 12v yellow) for any voltage. I don't want you to damage your meter with the next step.

      If not zero, wait until they drop to zero before proceeding.

      If zero, change the meter to the Diode Check setting.

      Check the 3 outputs with the red probe and report the readings.
      You can probe them on P2 if it's easier. Expecting readings of 0.030Ω to 0.300Ω
      I am following this ancient thread trying to troubleshoot an identical supply and have reached this step as the first place where the conclusions might be different.

      Probing the outputs forwards, I get:

      Yellow ~0.160
      Red ~0.020
      Orange ~0.104 after a longer delay

      Probing the outputs in reverse, I get:

      Yellow ~0.135
      Red ~0.020
      Orange ~0.109

      Probing VDC on the cathode side of D2 shows a spike well over 300V. However the voltage here when the supply is off is about 93V not 160V.

      Suggestions welcome, if anyone can remember back this far.

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