Date   : Thu, 25 Aug 2005 15:11:41 +0100
From   : "Jules Richardson" <julesrichardsonuk@...>
Subject: Re: Master 128 PSU ticking

> >Hi,
> >
> >I have a M128 with a PSU that generates a ticking/pulsing sound when
> >turned on. The sound appears to be coming from the middle of the PSU
> >somewhere. The M128 does not power up.
> >Has anyone experienced this before and is there a fix?
>
> Ticking is usually a sign of a short somewhere on the output
> power rails..

Actually it can also be a result of too little load - the supply tries to
start up, finds itself unable to regulate the output voltage and then shuts
down quickly, before everything repeats.

Usually switchmode PSUs just monitor and regulate on the main voltage rail
(5V in this case), so putting a dummy load on this rail alone and then
checking all output voltges would be a good place to start I suppose. (I
tend to be lazy and use an old scrap hard disk as a dummy load for supplies;
it normally draws enough current on the 5V rail to convince a supply to try
and start up normally)

A visual inspection's probably a good place to start after checking outputs
on a meter - look for broken solder joints or obviously leaking capacitors
etc.; then probably follow that with a check of any larger diodes on the
output stages.

cheers

Jules