Dead PSU

From: Max Eskin <>
Date: Sat Jul 4 17:22:15 1998

I counted with a stopwatch. It beat very fast, so it might be even
higher than 120Hz, but it certainly is much higher than 60. I don't know
if they'll actually let me do this repair anyway.

>I think we need to determine if it really is a 120Hz ripple, or
>near it. If it really is 2* mains frequency, then start looking around
>the mains smoothing capacitors first.

It's a very simple PSU, there's a bunch of capacitors, a single small
chip, and a couple of every other component and that's it. This does not
have the power-on from the keyboard thing. It uses a regular button
which cuts mains off from the rest of the PSU. Two questions: what is
the definiton of a Switch Mode PSU, and what is a Crowbar?
>> Don't worry about the complex circuit with thround resistors and
>> little capacitors, it's working becasuse of that fluttering fan and
>> it did power up when you commanded it to turn on by the keyboard.
>Agreed. This doesn't sound like a control circuit problem (although,
>having seen some strange SMPSUs in my time I'd not bet my life on it!.
>few, a very few SMPSUs have a separate linear supply for the control
>circuit that can inject mains frequency ripple).
>> Jason D.

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Received on Sat Jul 04 1998 - 17:22:15 BST

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