Date   : Tue, 31 Aug 2004 12:46:27 +0100
From   : Chris Jones <chris@...>
Subject: Re: Master 128 PSU info.

Robertpatton41@... wrote:
 > ...
> In most cases these units provide no output as the 1.6A fuse has blown. 
> Replacing it causes it to blow (spectacularly!) again.  Any suggestions 
> as to likely causes, please?

In my experience of repairing switch-mode supplies in general, the first 
place I look when the fuse blows violently is the bridge rectifier at 
the mains input. Frequently one of its diodes goes short circuit. The 
next most likely cause is a short-circuit chopper transistor, but that's 
difficult territory because there's frequently something more subtle 
which has caused it to die, a dried-up (low in value/high in ESR) little 
electrolytic capacitor mounted somewhere hot being a prime candidate.

The usual caveats about voltages high enough to kill you apply, of 
course: *don't* tackle any of this unless you're confident about working 
with components charged to 350V or more, even after the unit is switched 
off and apparently dead, and know exactly where to expect them.


HTH
Chris
-- 
Chris Jones - chris@...        
http://www.stumpie.com/