Path: utzoo!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!samsung!think!snorkelwacker!mit-eddie!mit-amt!dlleigh
From: dlleigh@mit-amt.MEDIA.MIT.EDU (Darren Leigh)
Newsgroups: comp.sys.amiga
Subject: Re: A2000 Power Supply
Summary: yes, they are fixable cheap
Message-ID: <1739@mit-amt.MEDIA.MIT.EDU>
Date: 2 Mar 90 20:08:04 GMT
Reply-To: dlleigh@media-lab.media.mit.edu (Darren Leigh)
Organization: MIT Media Lab, Cambridge MA
Lines: 68

In article <8249@pt.cs.cmu.edu> dpm@k.gp.cs.cmu.edu (David Maynard) writes:
>
>A friend of mine has an Amiga 2000 that stopped working a few weeks ago.
>When he turns it on, the power light comes on for a few seconds and then
>shuts off.  He disconnected the power supply and discovered that it will...

The power supply in my 2000 broke about a year ago.  The LED wouldn't
even stay on for a few seconds -- it would turn on and then off again
almost instantly.  I'm not sure what is causing your failure, but you
should not try a component level fix of a power supply unless you
really know what you are doing.  Remember that you have thousands of
dollars of equipment relying on this power supply, and one bad glitch
could trash it all.

>So far he hasn't found anywhere that has the power supply in stock.  It

Deja vu.

>looks like it will cost ~$180 when places do get them.  So the question is,
>can we hook up a standard (~200W ?) PC power supply?  The Commodore supply
>only lists +5, -5, +12, and -12 voltages which are all standard, so it would
>seem that a little custom cabling (and a large, ungainly external power
>supply) would fix things for <$75.  Would he need to add a cooling fan to
>the enclosure (it is currently a 2-floppy system with no expansion boards)?

I'll tell you what I did that fixed mine for about $50.  First the
disclaimer:

DISCLAIMER: The following is provided for informational purposes only.
I make no claims that this will work for your system or that it can be
done safely.  The equipment described contains hazardous voltages and
should only be opened and modified by trained personnel.  If you don't
know what you're doing, take it to the shop and let someone who does
fix things.  Otherwise you are endangering your equipment and your
life.

I first got the idea of just replacing the entire internal power
supply.  I ordered a really small (in physical size) PC clone supply
(I think it was 150W), but when I got it, I found that it would not
quite fit inside my case.  Remembering that most of the clone hardware
is made by the same companies and that defacto standards abound, I
checked inside the metal cases of both the Amiga and clone power
supplies.  It turned out that the power supply board inside each was
the same size.  I put the clone board inside the Amiga power supply
case, added a little custom cabling and voila!  The one subtelty was
that was that I had to change one of the jumpers on the 2000
motherboard.  The amiga power supply has a TICK output which is a TTL
60Hz signal derived from the power line.  Your new power supply
probably won't have one of these so you need to tell your Amiga to use
the VSYNC signal instead.  I think it's jumper J200, but I don't have
the docs with me.  Check the schematics in the back of the user
manual.  The problem with this is that your real-time clock will only
run at 59.94/60.00 the proper rate.  This is significant over the
course of a single day, so you'll need to run "setclock load" at least
that often.  If you're serious about having a clock run at the right
speed, you can generate your own 60 Hz tick signal.  If you generate
this from the power line, PLEASE be sure to isolate it properly.

Just using the entire PC clone supply externally would also work, but
it would be ugly and less portable.  You'll still have the clock
problem too.  Putting a fan inside the 2000 (even though the power
supply is external) would be a good idea.

Please e-mail me if you have questions, problems or success stories.

Darren Leigh
dlleigh@Wmedia-lab.media.mit.edu (Internet)
mit-amt!dlleigh (UUCP)