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Display Issue

PostPosted: Thu Mar 23, 2017 6:29 pm
by MedicGoalie84
just acquired a PCjr, and when I power it on there is no display. The fan on the floppy drive is working, the floppy drive itself appears to be working. There is audio out, just no video. I have tried with composite out and a PCjr monitor, neither of them are showing anything. I've looked at both sides of the system board and everything looks fine. The traces are intact, there are no scorch marks or signs of excessive heat. None of the chips appear to be damaged, and the capacitors all look good.
I'm starting to think that it might be the Motorola 6845 chip, but I am unsure of how to test it. How should I go about continuing to troubleshoot this?
Edit: It would seem that disassembly did the trick! I'm still not out of the woods yet though. The output to the monitor does not appear to work, though composite is fine. If I try to run FS 2.0 the composite signal cuts out completely. The monitor seems to be working Ok (lack of display notwithstanding), I opened it up and there were no signs of damage to any of the components (I'm not that comfortable doing anything beyond looking at this point when it comes to CRT monitors). Does this mean that I need to start looking for a new monitor?

Re: Display Issue

PostPosted: Fri Mar 24, 2017 1:12 pm
by Vorticon
Did you check the connector? I have intermittent display issues with it. There might be some dirt or corrosion in there.

Re: Display Issue

PostPosted: Fri Mar 24, 2017 3:38 pm
by Trixter
The most basic test for a PCjr is getting output from the composite connector. If you're not getting that, don't bother opening up the PCjr RGB monitor because the problem is at the source.

You wrote "composite is fine" but later wrote "FS 2.0... composite signal cuts out completely" so I'm not sure how to interpret those results. Did you try other games that support Composite color output? FS 2.12 is the only version I've run on a PCjr that works 100% correctly, maybe try that specific version?

The "is this PCjr monitor basically working" test is to unplug the video source and turn it on. You should get a pure white screen that fills all overscan areas.

If disassembly "helped", then you may have cracked traces, dodgy solder joints, or some corrosion somewhere. I'd look at it again just to see if anything stands out.

Re: Display Issue

PostPosted: Fri Mar 24, 2017 10:14 pm
by MedicGoalie84
Sorry for the confusion, I can get composite output, I even ran it through through test tag 4 and 8 without any issues. However when I try to run flight simulator (upon further review I do believe it is 2.1, it says it is for PC and PCjr), the display signal cuts out, or at least my TV tells me that the signal is gone. I've looked over the disk in DOS and there were no read errors, so I don't think it's a disk issue. I also tried a copy and had the same result.
When I turn on the monitor and it is not hooked into anything the screen stays black, there is no white screen. The connector looks clean with no signs of corrosion.
I hope that helps with the confusion. And thank yall so much for your input!

Re: Display Issue

PostPosted: Sat Mar 25, 2017 11:18 am
by Trixter
If the composite color tests in the diagnostics is 100% successful, that's a very good sign that the PCjr's video output is ok. I am blaming Flight Simulator at this point (does it display a menu when it starts up? If so, are you picking the "composite" option?) Try some different software that supports composite color graphics.

If you turn on your monitor with it not connected to anything, and you see only black, that's not good. Try fiddling with the brightness and contrast knobs; you should be getting a completely gray or white screen with nothing connected. If you still don't get a picture, then I'm leaning towards your monitor being faulty.

Re: Display Issue

PostPosted: Sat Mar 25, 2017 1:03 pm
by MedicGoalie84
I'm inclined to agree on the monitor being bad. I don't really have that much in the way of software (yet), the only thing I've been able to load so far that is not in black and white is PFS write, and that works fine, I just can't read it because as far as I can tell it is 80 column only. With Flight Simulator the signal cuts out while the game is still loading before any part of it can display. The computer also came with GEM Desktop (I don't know which version), and that does the same thing.

Re: Display Issue

PostPosted: Sat Mar 25, 2017 3:45 pm
by Trixter
If you have a DOS boot disk, you can put the system into 80-column B&W mode with "mode bw80". PFS:Write will likely be easier to read if you do that.

Re: Display Issue

PostPosted: Mon Mar 27, 2017 6:06 pm
by MedicGoalie84
That worked a treat thank you so much!!!