Date   : Tue, 31 Aug 2004 10:54:20 +0000
From   : Jules Richardson <julesrichardsonuk@...>
Subject: Re: Master 128 PSU info.

On Tue, 2004-08-31 at 09:37, Robertpatton41@... wrote:
> Apologies if you've received this once before. There is doubt whether
> I was actually subscribed when I sent it. (Does AOL work OK on this
> system?)   

Seems to be working!
>  
> Replacement PSUs for the Master128 are becoming scarce, so I must try
> to repair the six "duds" in my possession.
> Can anyone provide me with a circuit diagram of this PSU please? 

Hmm, I don't think I've come across that anywhere. However, the
following general info on switch mode PSU repair is probably useful:

http://repairfaq.ece.drexel.edu/sam/smpsfaq.htm

In particular from the intro:

"Supply dead, fuse blown - shorted switchmode power transistor and other
semiconductors, open fusable resistors, other bad parts. Note: actual
cause of failure may be power surge/brownout/lightning strikes, random
failure, or primary side electrolytic capacitor(s) with greatly reduced
capacity or entirely open - test them before powering up the repaired
unit."

If you don't have an ESR meter for testing caps with, there's details of
a nice homebrew unit at:

http://www.albany.net/~gwoods/esr_meter/esr_meter_index.html

> (The  servicing manuals published on the web do not include the PSU.)

That seems typical of Acorn; PSU diagrams for any of their equipment
seems hard to come by. I suppose they were farmed out to various
manufacturers over time and not designed by Acorn themselves.

cheers

Jules