PCjr monitor repair

[hargle]

I have 3 PCjr monitors that are showing signs of their age.

#1 - no vertical hold. There doesn't appear to be anything gumming up the connector on the cable. Colors appear to be good when I can see them.
#2 - yellowish and dark. the monitor is just dull and anything that should be white looks like the teeth on a 60 year old smoker.
#3 - white out. At first power on, I can see the monitor displaying the IBM logo, but within 4-5 seconds the image is gone and the entire screen is white.

yes I've fiddled with the knobs on all of these and nothing helps. I have not taken any of these monitors apart yet.

My skillset in fixing monitors is limited- I have no desire to poke around around the yoke or tube. a chip replacement on a circuit board that drives the monitor would be doable. I don't want to play with big scary capacitors.

Any advice on what I should do with these 3 is greatly appreciated. At the end of the project, if I had 2 working monitors and a pile of parts from the 3rd, that's ok, but I'm not sure which bits to take from which ones. Which of these sounds easiest to fix?

 

[Stone]

The flyback is a likely culprit on some of them.

 

[mbbrutman]

There are additional adjustments you can do with the back cover off. That should take care of #1 and #2. Not sure what is going on with #3 ...

I also have the wiring diagrams around here somewhere. It's based on a very similar Mitsubishi model.


Mike

 

[wesleyfurr]

Not to hijack the thread...but I would be interested in hearing about the solution to the one with the #1 vertical hold issue as well. I've got one that won't stay still. I can adjust the v-hold and get it darn close, but it still keeps rolling one way or the other.

Thanks,

Wesley

 

[SomeGuy]

Not familiar with the PCjr monitor, but what I would do is start by opening the cases and get a good visual inspection of the logic board, and look for anything obvious that might be damaged or loose.

As mbbrutman pointed out, there should be some potentiometers on the main logic board can try adjusting.

My thoughts on each:

1: possibly a component failure in a low voltage part of the vertical. Possibly adjusting the internal pots might help. Check the continuity between the pin on the connector cable to wherever it is supposed go on the logic board to completely rule out any issues with the plugs. A schematic and an oscilloscope would really be needed to narrow things down, but in general work up from the input and around whatever IC controls that.

2: Pots on the logic board should let you adjust the brightness further than external controls. If that doesn't help sufficiently, it could be a problem with the tube itself. An easy way to determine that would be to put the logic board in monitor #1. Nothing you can do about a weak tube, but then at least then you would have one working monitor. I doubt this is a problem with the HVU/Flyback, if it were, you would probably hear a loud high pitch noise and the screen contents would likely appear wavy.

3: that is very strange. Is it constant about when it goes "white" after being powered on? Does it make any difference (longer, shorter) if it has been on for a while? Does it go white instantly, or fade to white? If it is instant and varies, it might just be a bad solder connection somewhere. Does giving it a whack do anything?