Re: IBM 5150: What happened!?

thewises wrote:

Marten Kemp <martendespamkemp@xxxxxxxxxxxxxxxxxxx> wrote in
news:xz3if.3888$aA2.1095@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx: 


thewises wrote:

"David L. Beem" <David@xxxxxxxxxxx> wrote in
news:43877325$1@xxxxxxxxxxxxxxx: 

"thewises",


Oh, no. This power supply was 165 watts. As far as the old power
supply(which was 120 watts), it was dead when I got the computer.

I'm with Rick here. You have a short somewhere. The hard drive
is the most common suspect (do I have it right that with the bad PSU before
you haven't seen the system be operational?).
I'd take the system apart for examination. Look at both PSUs to
see if you can find out if it is the +5 or +12 rail (I doubt it would be the
others, as they are just used on the motherboard). With the handy use
of a voltmeter you might even see which component is shorted
(electrolytic capacitors are known to leak & do this).
Swallow pride & open your mind to not discount suggestions
because you think you have done everything right. With the system in an unknown
condition it could be where the previous owner just gave up on the
problem. Once you are certain there is no shorts on the components,
test from least suspects (like just the motherboard & video card
alone) forward with another PSU.

I did remove the floppy drive(big full-height Tandon drive) and stuck
in my old 133Mhz Pentium, and it worked fine. As far as the other
stuff, the video card is a full-length MDA card. I can't test that
because the Pentium's power supply doesn't have a pass-through, so
there's no place to plug the monitor(since the 5151 monitors use the
pass-through). My 386 has a pass-through, but I think the case is too
short to fit the video card. 

About the hard disk, I suppose I could put that in the Pentium(along
with the controller card) and see if it works, so I can find at least
find out what's on there.

But I don't believe that the hard disk ate the power supply. Lots of
people used hard disks in IBM 5150s, mostly because they wanted a
hard disk, but didn't want to pay for an XT.


Plug a standard PC power cord into the pass-through monitor plug.
There's no magic in the pass-through port on the power supply.

If you have a meter try checking for dead shorts on the +5V and
+12v power leads ofthe hard drive first, then don't go to the
trouble of mounting the hard drive in a computer to test it. Just
plug it into a power supply and see if it spins up. Sit it with
the circuit board on the top when you test, though. I've fried
a couple of drives by being careless that way.

Ok, I did what you said. I put the MDA card in the Pentium and plugged a power cord into the monitor plug. I performed a clean DOS boot and switched the MDA card to active by typing MODE MONO. And sure enough, the DOS prompt appeared on the 5151 monitor. So now I know the video hardware works.

But more importantly, I sat the old power supply on the floor and plugged it into a wall outlet. I flipped the switch, and the fan started spinning, which it did not do when it was in the computer. So maybe there is something in the computer that's preventing the power supply from working.

If you have a volt meter check the +5V and +12V outputs,
mainly because they're easy to check (+5V on one side and
+12V on the other, with the grounds in the middle).

Did you try to shake the system unit, looking for a rattle
that indicates a loose mounting screw, or just remove the
system board from the case? You can get a dead short across
a pair of traces on the system board. Remove the offending
object and you have a good chance that the PC will run just
fine (yeah, I've had that happen, too).

--
-- Marten Kemp
(Fix name and ISP to reply)
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