Zenith Z-100 Power Supply Problem
Charles Richmond
me where to get a *replacement* supply that is a switching supply,
instead of replacing it with an original supply with a big honkin'
transformer???
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| Charles and Francis Richmond |
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| plano dot net at aquaporin4 dot com |
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Barry Watzman
NOT have a "big honkin' transformer".
Is this for the "low profile (Z-110 series) or the "All-in-One" (Z-120
series)? What is wrong with the power supply? I ask, because there are
no replacements available, in general, anywhere at any price (unless you
run into someone who has a spare, or buy an entire Z-100 just to steal
the power supply).
As I mentioned to Herb, I have a schematic. Getting it fixed may be the
best solution if you can find someone who can do it.
Barry Watzman
Wat...@neo.rr.com
Charles Richmond
You and Herb have been very kind to reply to my problem. The Z-100
is a system a friend of mine gave me. I have *not* done much with
it yet, but I was under the (mis-)impression that it had a
transformer. I do *not* have money to put into it right now.
I thought this might be a good question to ask now, while there
still *is* a Z-100 Usenet group!!!
Barry Watzman
Charles Richmond
watched to prevent this kind of thing!!! :-(
Herbert Johnson
> You and Herb have been very kind to reply to my problem. The Z-100
> is a system a friend of mine gave me. I have *not* done much with
> it yet, but I was under the (mis-)impression that it had a
> transformer. I do *not* have money to put into it right now.
>
> I thought this might be a good question to ask now, while there
> still *is* a Z-100 Usenet group!!!
The following applies to many kinds of switching power supplies, other
than specific component values.
If you have a voltmeter and ohmmeter, you can still do some tests for
free. It would be helpful to describe the problem and symptoms. Did it
fail some time after power up, did it power up very briefly, or did it
not power up at all? Did you smell or see smoke, a flame, a flash of
light? What kind of smell? All of these are diagnostic events.
The input to the power supply amounts to a switch and fuse and a full-
wave rectifier to some large capacitors. There is also a noise filter
circuit on a small separate board, which is probably OK. Unplug the
Z-100 from the AC line, turn on the Z-100 power switch and put the
ohmmeter across the AC outlet on the Z-100 supply. It will probably
read megaohms, suggesting a blown fuse. But the failing component
likely shorted to blow the fuse. It is a 6A fuse, a 3AG type available
from Radio Shack - see my previous post for a link to my Web page
about this.
If there is low resistance across the AC input, then the fuse and AC-
side circuits are likely intact. You may have a short on the DC side
of the power supply at one of the S-100 boards or video board or the
motherboard. If there is a shorted tantalum capacitor on one of those,
the power supply will shut down and only come up briefly - that's a
good thing.
If you disassemble the power supply, you can measure components like
the full-wave bridge rectifier, looking for shorts. Or check the fuse.
Look visually at the fuse; is it simply open (your ohmmeter will tell
you) or is it BLASTED inside with black stuff? The latter suggests a
short somewhere on the AC side, and not just a power surge.
These are the sorts of tasks and procedures one needs to do, to fix
these switching supplies or at least diagnose the problems. My Web
page goes through these issues, to educate and encourage people to do
their own repairs, to obtain parts and instruments I discuss, and to
learn more about their computers at the component level. This is
completely practical to do for 1970's and early 1980's computers, even
decades later because parts are still available, the tools mentioned
are cheap. But the skills and the "I can fix that" presumption, are
becoming a "lost art", as practitioners of repair are becoming an
"endangered species".
Herb Johnson
Herbert R. Johnson, New Jersey USA
http://www.retrotechnology.com/ retro-technology home pages
-- S-100, CP/M history by "Dr. S-100"
email: hjohnson AAT retrotechnology DOTT com