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?

54 responses total.

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).

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...)

I can get a refurbished monitor from Micromend for about $30 (last I checked).
I'm obviously looking for the cheap way out.

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.

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?

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?

Perhaps you should start by cleaning or replacing the intensity
control.

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. 

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.

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.

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.

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.)

If the fuse is soldered in place, you may want to replace that.  Fuses
DO wear out.

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.

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!

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.

I answered aruba in email, if you want to post the reply, go ahead.

That email was before I got here ...heh

Thanks, guys - I'm going to open it tonight, and then I'll let you know what
I find.

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?

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.

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! 

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.

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?

They are prob. both power supplies.  The box with the thick wire going
to it generates 20,000 or more volts to attract the electrons, from the
electron guns, to the front of the screen.  The large component with the
wire going to it, is the flyback transformer.  That is what generats that
high voltage.  It may also include one or several high voltage diodes.
The "focus" knob controls how much voltage the flyback circuit generates.
I don't know what "screen" knob does.
If this is the part that blew, you may be able to fix it w/o too much
trouble.  The flyback transformer is most often driven by the horizontal
sweep transistor.  It is not uncommon for that or the flybach transformer
to go bad.  Try to find out what part blew.  (The flyback shorting out
may have also taken out the sweep X-sistor, etc.)

 !! 755am??? geeze, what kind of hours do you keep, anyway ????
  
reagardless, n8nxf is right on. The large thing in black potting
compound is the HV transformer. If that is blown (burned open) then
you hae to replace the most expensive part. It might be relatively
inexpensive part, but it is the most expensive anyway.
  
However - those HV circuits are "tuned" and there are other
parts whose eectronic values are selected for resonance.
  
I would presume (at first) that the flyback is not open and that
some other part is fried (one way or the other).
  
The "screen" adjustment is somewhat like a brightness control
limiting adjustment and also a setting that "pre-judges" the
range of the focus control.
  Worry about that later.
  
Have you contacted anyone about the repair costs?  Obviously,
to me anyway, and probably n8nxf, you have a HVPS fault which
is the fussiest/weakest circuit in a tv. 

My monitor now has a blown flyback, and I was told tht if it weren't under
warranty it would be an almost $200 repair.

I have a maybe simpler problem. My CGA monitor suddenly goes blank. 
It *seems* to be affected (but not much) by wiggling the intensity
control. I took it apart and ran benzine through the intensity pot, 
and it worked OK again - until recently. Now, its is back at its old,
unpredictable, tricks. It's hard to believe that a bad contact point
in the pot can be the problem, when rotating it doesn't always bring
the screen on again. Any suggestions? (I think I mentioned this a
long time ago somewhere..maybe.., but new ideas would be welcome!)

replace the pot, rcurl, or use wd40 on it. 

I've stayed clear of solvents that contain any residue, especially oil.
Is that really OK on pots? I would think it would hasten it getting
gummy.

I don't think I have ever replaced a bad pot.  I have come across 
many but a squirt of Color TV Tuner Cleaner has put them all into
"like new" operating condition.  The tuner cleaner contains a solvent
to clean the pot and a lubricant to keep the element lubricated.  In
days gone by, I've even used Vaseline to lubricate pot elements.  I
started doing this after putting together a RC servo kit and the 
kit included a small tube of Vaseline to lubricate the servo pot with.
I have never had a problem with treated pots getting gummy.  I, however,
would stay away from lubricants that get get gummy or turn to varnish
with time.

You assuage my fears: WD-40, here I come.

Thanks for all your help guys.  Does anyone have a response for #21?

From the Programmers PC Source Book, there are a bunch of
9-pin and 15-pin video pinouts provided.
  
For monochrome (MDA) 9-pin
        1- ground
        2- ground
        3,4,5- not used
        6- intensity
        7- video
        8- horizontal
        9- vertical
  
There are monochrome-identified outputs in each of the
color video outputs as well. 
  
The VGA 15-pin connector *seems* to have both digital and
analog outputs. The green/monochrome output is pin 2. The
green return (analog ground) is pin 7. Horizontal drive is
pin 13 and vertical drive is pin 14. Pins 11 & 12 indicate an
+input+ to the computer for monitor sensor 0 (pin 11, digital
ground, color) and monitor sensor 1 (pin 12, digital ground,
monochrome). 
  
The only voltages listed are 0.0 to 3.5 vdc so we are not
dealing with life threatening stuff here.
  
I +suspect+ that a scope would help, just to look at stuff, but
that monochrome monitor is about the same thing.

My roommate's monitor is being fixed at Computer Medic, for about $100.
They said they had to replace the "deflector card" (not shield or dish,
mind you, but card).  In the meantime we've been trying to get the mono
monitor to work with the VGA card, but haven't had much luck yet.  I tried
doing what TS suggested, I connected pins in this way:

Monitor pin       VGA card pin
-----------       ------------
1                 7                ground
2                 11               ground
7                 2                video
8                 13               horizontal drive
9                 14               vertical drive

We get some noise on the screen (starting when the horz. and vert. drives
were plugged in), but that's it.  We've got a printer plugged in and hit
Ctrl-PrtSc at the start, so we know we're in DOS and sending text to the
screen.  When I do a "MODE MONO" from DOS, the screen goes blank for a sec
but comes back the same as it was before.  (It's not quite obvious to me how
to count the pins; could someone clarify that for me?)
   I went to Radio Shack to ask if they had a connector to do the above,
and the guy there told me that I could plug the mono monitor right into the
serial port, and it would work, as long as I took the VGA card out first.
It didn't work when we tried it, but is there any truth to what he said?

Hmmm, ask for that "deflector card" to be returned to you - i've
never seen or heard of such an animal in a crt circuit.
  
I don't have the time to analyse the configuration you tried, yet,
but I will, rsn. However, the two grounds are +different+. 
  
The pin numbers are +usually+ molded into the plug - use a
bright light ... and maybe a magnifying glass ... and also
look on the opposite connector, the numbers might be visible
there.

I suspect the "deflector card" has the horz. sweep drive circuitry on it.
I suspect}i this card drives the deflector yoke towards the back of the CRT.
This yoke deflects the electron beams from the electron guns up/down and
left/right.
 
So far as driving a MONO display from a VGA card, my guess would be that you
need to change some jumpers on the VGA card to tell it you'r driving a MONO
display.  Look at the manual that came with your machine or spend $15 for a
new MONO card ;-)

Aha!  - methinks me has it .... (it's contagious  watch out) ...
  
That pin 11/12 stuff on the card is a sensor/switch. The VGA
card itself has it's own digital ground (deparate from analog
ground). 

The card provides this digital ground on its pin 10. Apparently,
and with the excellant guess above, that "jumper" idea is
waht is necessary - Pin 12 (monitor sensor 1) is what needs
to be grounded for the VGA card to select mono. Pin 11 is
what is grounded so the card know color is needed.
 
On the card connector, jump pins 12 to 10 sothe vga card
will know what is expected.
  
leave pin 11 open. 
  
And a couple of other considerations ... the H and V rates
*might* be different (frankly, i dunno) - so tweek the 
horizontal hold and vertical hold controls, well, twist the
heck out of them if necessary to see if you can lock the
stuff up right.
  
"Noise" on the screen usually can be analyzed best in person.
  
One last thing - the MDA output has an "intensity" pin.
  
Currently you are leaving that pin open. That amounts to
a brightness control in effect. You might want to see if
connecting that pin 6 (intensity) to the VGA pin 2 (mono
out) as well as having VGA pin 2 also connected to the
MDA pin 7 (video).

   Well, we have a bigger problem now.  While the monitor was gone, I had
the computer running with a printer attached, and could see that DOS was
running fine.  I tried TS's pin configurations to get the mono monitor to
work, to no avail.  Then I turned off the mono monitor, and turned off the
machine.  The next time I turned it on, the monitor was still wired in,
but was off.  The computer wouldn't boot.  It spun the hard disk once, but
didn't get as far as hitting the A drive, which the CMOS is set up to do. 
I unplugged the monitor right away, of course, and tried again, but no
luck.  Nothing we have done has gotten it to boot.
   Thinking that the video card might be fried, I took it into work and
tried it in a 486 at work, and it worked fine.  (I had a bit of a scare
though - when I put the 486's original card back in it wouldn't work at
first - I had to take the card out and reseat it (and hold my breath)
before it worked.  For a second I had a vision of a virus that inhabited
video cards.)
   We picked up the fixed monitor today (we saw it working at Computer
Medic), and plugged it in, and ... nothing.  No action on the screen at
all.  I'm at a loss at this point.  Anyone have any ideas?  Help!

- Backtalk version 1.3.30 - Copyright 1996-2006, Jan Wolter and Steve Weiss