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From: hans@umd5.umd.edu (Hans Breitenlohner)
Newsgroups: comp.sys.atari.8bit
Subject: Power supply problems on 130XE
Message-ID: <1812@umd5.umd.edu>
Date: Thu, 23-Jul-87 19:14:08 EDT
Article-I.D.: umd5.1812
Posted: Thu Jul 23 19:14:08 1987
Date-Received: Sat, 25-Jul-87 09:14:18 EDT
Reply-To: hans@umd5.umd.edu (Hans Breitenlohner)
Distribution: world
Organization: University of Maryland, College Park
Lines: 25

I helped a friend with a power supply problem on his 130XE this weekend,
and thought I would pass on what we found in case anybody had similar
problems.  

He had expanded a 130XE to 320K, and everything seemed fine.  Then he
expanded it to 576K, and everything still seemed fine.  But after a
while the following problem occurred:  After the machine had been on for
an extended period (many hours to a day), and then was turned off, it would
not power up correctly.  The screen would turn black, and nothing else
would happen.  Turning it off for a while seemed to fix the problem.

With the help of a scope we found that the power supply, when hot, would not
supply 5 volts on powerup.  It would oscillate at 105 kHz around 3 volts.
The unit pulled only 900 mA, and the supply is rated at 1.5A, so overload
was not a problem.  It turned out that any disturbance, such a inserting
a VOM in the supply line, would make the problem disappear (which made 
chasing it down real fun!).  The final solution was to put a small choke
(about 10 micro-Henry, but I don't think the value is very important) into
one of the power supply output leads, and the problem has not been seen
since.

I don't know if this is typical behavior or if the power supply was defective.
Does anybody know what kind of regulator is in the supply?

It was great fun, I hope somebody can use this info.