[Intel-devsys] switching power supplies

Jack Mcmullen forjack842 at aol.com
Fri Aug 23 11:21:25 MDT 2019

The switchers aren't black magic. One needs a isolated variac, load resistors, stock of good ESR caps.90% of the time the caps fail due to cap aging. Like old electronics the output supplies caps need to be rep[laced.Regulation is by pulsing feed back generated by a voltage sensing circuit driving a opto coupler LED. The receiving transistorenables/disables the power inverter. Typically the 5v or 12 volt main is the controlling voltage with the rest slave regulated.

-----Original Message-----
From: Herb Johnson <hjohnson at retrotechnology.com>
To: Discussion list for Intel development systems <intel-devsys at lists.brouhaha.com>
Sent: Fri, Aug 23, 2019 9:10 am
Subject: [Intel-devsys] switching power supplies

Some months ago, Bill Beech and I posted about our struggles with Intel 
systems which used a now-failing switching power supply. Bill "fixed" 
his by buying a modern working switching supply for modern PCs.

Recently, I was contacted by someone who has an early 1970's 
minicomputer. They diagnosed by swap and other means, their particular 
switching supply had failed. They wanted me to fix it; I've told them I 
cannot, but I at least identified their power supply was probably an 
"OEM" model not designed (or documented) by the computer's manufacturer.

That's the same situation Bill and I found ourselves in. But this older 
supply produces 24 volts, which is uncommon in modern supplies. And it 
may be harder to swap-in something modern.

So I'm asking: has anyone come across a repair-service, that can fix 
switching power supplies "cold" - no docs, without sending them the 
whole computer? I'm sure companies offer such services - a Web search 
will find those. I'm asking for real (and current) experiences, not for 
a Web search I can do.

Of course, many Intel development systems did not use a switcher. But 
some did, and my friends here have experiences with other systems.


Herbert R. Johnson, New Jersey in the USA
http://www.retrotechnology.com OR .net
preserve, recover, restore 1970's computing
email: hjohnson AT retrotechnology DOT com
or try later herbjohnson AT retrotechnology DOT info
Intel-devsys mailing list
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