imsai 2

From: Richard Erlacher <>
Date: Tue Aug 17 21:54:21 1999

Assuming you've used a real wire, it certainly will keep the two points at
the same potential. I thought you meant bypassing the already installed
regulator by attaching a feed directly from the power supply, which
indicates what I was thinking rather than what I should have been. What I
was trying to envision is what kind of external booster they intend to put
on a PC PSU.

I can't imagine any worse sort of arrangement, though. By this I mean that
the one functional component which seems to fail most is the power supply.
WHile I've only had about half a dozen motherboards die over the years, I've
got a 55-gal drumful of dead power supplies, on most of which the fan is
what failed. In many cases, the fan fails and then the supply gets hot and
dies. The common PC PSU is overdesigned by a fair amount. I doubt that a
single 250-watt PSU is adequate for a typical S-100 setup. I know, that's
50 Amps on the +5! I've never seen one supply, even a 450-watt server
supply that could approach its rated loading. They're out there, I'm sure,
but I've never encountered one.

Back to IMSAI's problem . . . I can't see financial justification for
booster supplies from a PC PSU when you can buy a 450-watt open-frame
switcher and set the outputs to the required voltage and be done with it. A
day's work behind making the decision will eat up all the savings associated
with using a PC PSU.


-----Original Message-----
From: <>
To: Discussion re-collecting of classic computers
Date: Tuesday, August 17, 1999 6:46 PM
Subject: Re: imsai 2

>>I'm not sure that "jumpering across" the 7805 will be healthy for the
>>Of course, if the input doesn't drop below the output during shutdown this
>>may not be a concern.
>Maybe I was unclear on what I meant by "jumpering across": you put a
>wire between pin 1 and pin 3 of the regulator. With such a jumper,
>it's impossible for the input to drop below output at the regulator.
>Of course, you've got to remember to remove the jumper before putting
>the resulting card back into a system with unregulated power busses!
>Like I said, regulated S-100 power busses were done by several
>in the early and mid-80's with great success. It's a non-issue.
> Tim Shoppa Email:
> Trailing Edge Technology WWW:
> 7328 Bradley Blvd Voice: 301-767-5917
> Bethesda, MD, USA 20817 Fax: 301-767-5927
Received on Tue Aug 17 1999 - 21:54:21 BST

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