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| Author |
Message |
fes
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Monitor help needed (a good cause)
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Aug 24 15:39 UTC 1991 |
I have a number of dead/buggered/otherwise-infirm pc monochrome monitors. Some
of them are Magnavox PC-80s for which I have schematics. For all I know about
electronics, my dog might as well have the schematics. Anyway, here's the deal:
I am donating a functioal PC to the Unitarian church and I need to have one of
these monitors fixed. I have two right now that work except that the bottom of
the screen is badly compressed (lines of characters on the bottom third are
compressed to the point that they look like bright underlines). If someone can
help out by fixing one, the Anyone?
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| 54 responses total. |
fes
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response 1 of 54:
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Aug 24 15:40 UTC 1991 |
and that got buggered by line noise - what I'm trying to say is that if anyone
can fix one of them for me, they can have the other one (and a few others if
theyre interested).
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aaron
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response 2 of 54:
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Aug 24 16:15 UTC 1991 |
I had a similar problem with a TV, that cost about $90 to have repaired.
(Although, I can't say that line noise was buggering my TV... Perhaps
you should remind your line noise that Michigan has a sodomy law on the
books...)
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fes
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response 3 of 54:
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Aug 24 21:53 UTC 1991 |
I can get a refurbished monitor from Micromend for about $30 (last I checked).
I'm obviously looking for the cheap way out.
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klaus
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response 4 of 54:
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Aug 26 11:04 UTC 1991 |
If I had the time, I could fix it for you. Unfortunatly time has become
a scarce commodity for me. Seems to be a problem in the vertical sweep
circuit. For some reason it's not generating a linear ramp.
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fes
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response 5 of 54:
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Aug 26 20:00 UTC 1991 |
My wife has decreed that (since I usually keep my hardware stash in the attic)
these monitors can no longer reside in their current location. I don't want to
put them in the attic and I hate to throw them out. Anyone want them?
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rcurl
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response 6 of 54:
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Aug 29 18:43 UTC 1993 |
My CGA Zenith ZVM-133 monitor is showing symptoms of its age. The screen
blanks, but I can get it back by wiggling the intensity control - usually
by turning it up all the way and jiggling. Then I can back off, until
the next time it blanks. Generally the screen is totally blank when it
goes, but once I noticed that some letter components of a display
stayed (though I don't recall which, and what color they were). Does anyone
recognize these symptoms, and know what to repair?
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danr
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response 7 of 54:
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Aug 29 20:18 UTC 1993 |
Perhaps you should start by cleaning or replacing the intensity
control.
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rcurl
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response 8 of 54:
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Aug 30 04:40 UTC 1993 |
That sounds like a good start. But why would *part* of a display remain?
I have now determined it is the gray lettering from a WORD 5.5 window,
when using Colors 1. The blue (and most of the yellow mouse cursor) go,
but the gray parts remain as white. Weird.
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danr
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response 9 of 54:
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Aug 30 10:53 UTC 1993 |
Hmmm. That is weird. Perhaps it's because some spots on the screen
are naturally brighter than others and even under reduced intensity
they show up where others don't.
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rcurl
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response 10 of 54:
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Aug 31 00:51 UTC 1993 |
I checked the intensity control. Turning it dim is *not* the same as
the "blackout" fault, for the WORD5.5 window. What is grey in Color 1
comes up as what's left when the fault occurs. These would be white
in the default (no "color") mode. The fault if more complicated than
just a loss of intensity.
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n8nxf
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response 11 of 54:
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Sep 1 11:22 UTC 1993 |
My guess would be a cold or broken solder joint somewhere in the area
where the intensity pot is mounted. Moving the pot cleans the oxide
from the cold solder joint and it works for a while again. It
may also be the pot... I've seen the crimps where the pins on the pot
contact the resistive element, become intermitent. This can do weird
things to the circuitry aroud the pot, things that don't happen when you
simply thurn it up or down. i.e. like an open resistor.
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rcurl
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response 12 of 54:
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Sep 1 13:25 UTC 1993 |
I guess there is nothing for it but to go in with a hot iron. Are there
any other parts I should replace, while the patient is open? (I once had
an intestinal operation, so I asked the surgeon if he would snip out my
appendix, while he was in there. He gave me a disgusted look. I figured
it was because he could get his full fee for doing it separately.)
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n8nxf
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response 13 of 54:
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Sep 2 16:16 UTC 1993 |
If the fuse is soldered in place, you may want to replace that. Fuses
DO wear out.
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rcurl
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response 14 of 54:
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Nov 8 14:15 UTC 1993 |
I opened the monitor (r 6ff), exercised all the board connectors, and
gave the intensity pot a dose of paint thinner, while exercising same.
Display is now steady, and even reaches higher intensity. I think danr
was the monitor diagnostician in this case: it must have been an 8 year
accumulation of grunge in the pot. (But, we can't discount possible
bad contact in one or more of those dozen or so connectors.) Of course,
I forgot about the fuse, not having looked back here before starting
the job. Incidentally, the intensity pot must carry some significant
current - it is a 5K pot, connected to a pc board with a 3 pin molex
connector.
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aruba
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response 15 of 54:
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Nov 20 23:26 UTC 1994 |
My roommate's monitor just flamed out today. It's been jittery for a couple
of months, and today it started making sparky sounds, and smoking, and the
display went wild. Clearly (from the smell) something burned out. Can
anyone advise what to do about it? We're both pretty much software guys,
but I have used a soldering iron before. Is it possible this is something
we could fix ourselves, or should we take it somewhere, or what? Help!
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n8nxf
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response 16 of 54:
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Nov 21 12:57 UTC 1994 |
First thing to do is open it up and find the sourse of the noise and
smoke. If you are luck enough to find and replace the smoked device,
there is a good chance that it will do it again. In many instances,
the device that smokes was acting as a fuse. i.e. It smoked as a result
of another part failling. In that case it is good to have a schematic
to see if another component, connected to the failed part, might have
caused the failled part to fail.
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tsty
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response 17 of 54:
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Nov 21 16:05 UTC 1994 |
I answered aruba in email, if you want to post the reply, go ahead.
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tsty
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response 18 of 54:
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Nov 21 16:05 UTC 1994 |
That email was before I got here ...heh
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aruba
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response 19 of 54:
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Nov 22 01:04 UTC 1994 |
Thanks, guys - I'm going to open it tonight, and then I'll let you know what
I find.
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aruba
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response 20 of 54:
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Nov 22 06:23 UTC 1994 |
Well, I opened it, up, but I can't find anything that looks obviously
burned. The power supply still smells a little like the whole thing did
yesterday, though, so maybe that's the source of the trouble. Unfortunately
the power supply isn't on a separate card, it's attached to the mother
board with kind of a metal box around it. Is there anything more I can
do to diagnose it?
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aruba
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response 21 of 54:
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Nov 22 13:02 UTC 1994 |
I have another question too: my roommate has an old monochrome monitor
with a 9-pin plug. The color monitor which blew up has a 15-pin plug.
Is there any chance of getting an adapter so that he can use the mono monitor
until the other is fixed/replaced? The display card is some form of SVGA.
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n8nxf
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response 22 of 54:
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Nov 22 13:54 UTC 1994 |
Blown power suppy? It prob. has one of those switcher supplies, making
repair difficult and expensive. Fixing massive electronic servo loops
is a real !#**! even if you do have a schematic. You'll need to take a
very close look at the components on that board to find the blown one.
Look for tiny blisters in the epoxy cases of the diodes and transistors
or FET's. Good luck!
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tsty
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response 23 of 54:
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Nov 22 20:47 UTC 1994 |
I agree with n8nxf. And would add that a very close sniff test,
like get your nose w/in touching range of the parts, will help
isolate where the burn is.
What does the thick wire connect to? That's the thick wire that
goes to the side of the picture tube.
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aruba
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response 24 of 54:
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Nov 23 00:17 UTC 1994 |
The thick wire to the side (actually the top) of the picture tube
is going to the metal box I talked about, which means the box is the
power supply, right? It has inside it one really large component
encased in black insulation. On the side, it has two dials labelled
"focus" and "screen", though, which make me wonder if it really is the
power supply. There is another thing inside which is labelled
"High Voltage". Is *that* the power supply?
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