Testing Power Supplies! Re: Norsk Data Nord-10/S restoration effort on the way!

From: Joe R. <rigdonj_at_cfl.rr.com>
Date: Mon Nov 15 10:27:55 2004

   Testing power supplies before powering up a system is just plain paranoid! (And I'm trying to be polite here!) There are a thousand parts in modern computers that can cause just as much damage!!!!!!!! Just last week I THOROUGHLY tested a HP 1000 including running test on ALL of the firmware ROMs (About three dozen of them!) plus CPU tests, memory tests, PSU test etc etc etc. I'd had the machine running for several days testing it. THEN I connected the Floating Point Unit (this was a F series HP 1000). As soon I turned it on the internal memory tests started but it acted goofy. After removing the FPU and further testing I found that the FPU had toasted the CPU card :-( It has one bit in the Microcode section that's stuck high. I'm guessing it's a bus transciever or something similar since the stuck bit appears in every memory location and every register. (Anybody have schematics for the HP F-series CPU?)

   Further example: YESTERDAY I was testing a "new" HP 1000 (an E-series this time). A quick check of the PSU outputs showed it to be normal and we powered up the computer, cleaned and reseated some cards, reconfigured some cards, installed other cards, etc etc and powered it up and down numerous times over the course of several hours. THEN it happened! The PSU started making a loud sizzling sound and poured out copious smoke! All that testing and prior running gave no hint of the impending failure! What's more, this is the SECOND time that I've had a HP 1000 PSU fail after running for over an hour. FWIW I pulled the PSU out of another untested machine, put it in this one (without testing it!) and everythings working again.

   IF I had an absolutely unrepairable, irreplacceable computer and IF I had all the PSU specs and pinouts it MIGHT justify the trouble of testing a PSU before using it to power up a computer but otherwise forget it!

   Joe


At 11:13 PM 11/14/04 +0000, you wrote:
>> > Which is 11 years ago....
>> At the very most 11 years ago, which still isn't bad.
>
>I check the PSUs of machines that I own and have run before if I've not
>powered them up for, say, a year oe more.... It doesn't take long to do
>(especially not if you're familiar with the machine and/or have
>schematics), putting right the damage can take a lot of time and money.
>
>Most of the time you'll have no problems, sure. Most of the time when I
>get a machine on the bench (wheter a 'new toy' or something from my
>existing collection), the PSUs behave perfectly on dummy load. But if
>something does got wrong, you really don't want to kill all the chips....
>
>There is anotehr issue, actually. PSU problems -- marginally low
>votlages, ripple, and so on, can cause all sorts of odd behaviour that
>will take hours to find if you don't initially suspect the PSU (like the
>time my PDP11/45 would run for 1botu an hour and a half before falling
>over in all sorts of odd ways -- I traced that to a '+5V' supply to the
>memory that was actually about +4.6V). Checking out the PSUs can
>eliminate such problems.
>
>> I think it suffices to say that the guy who cut his teeth on the machine
>> and has supported them since 1986, and *owned the company since 1992*
>> didn't have any problems with it... He said that the PSUs were sturdy
>
>That would not be enough for me. Heck, the assurance of the designer
>wouldn't be enough for me (and nor, for that matter, would anybody else's
>assurance). The risk is just too great.
>
>Sure the PSU will have built-in protection -- all decent machines do
>(although HP omitted it from their desktop calculators for some unknown
>reason -- the HP9815, 9825, 9832, etc desparately need a crowbar!).But
>I'd rather not rely on it. Better to be safe than sorry.
>
>> I may have been mistaken, but at the time, as presently, I didn't see
>> the need to delve deeper into the PSU.
>
>All you need to do is disconnect the PSU from the machine, connect it to
>dummy loads (car bulbs are what I noramlly use -- 6V ones on the +5V
>line, for example) and check the output voltages. You don't need to
>investigate the internals of the PSU unless there's something wrong.
>
>-tony
>
Received on Mon Nov 15 2004 - 10:27:55 GMT