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IBM PS/2 Model 25 - Green Screen on Boot, No Post

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bushidounohana

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Apr 2, 2020
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Hello all!

Forgive me if this is already posted elsewhere, but I’m having trouble getting an old PS/2 Model 25 (8086) to boot up after digging it out of the closet. When I flip the power switch, the unit powers up (including power being fed to an add-on IDE hard disk attached to an expansion card that also feeds it power), but never actually posts, only displaying a dancing green screen. I took a look at the motherboard, reseated expansion cards and RAM, but don’t see anything terribly out of order, at least by my uninformed eye. Any one have any thoughts, tips, suggestions, or resources I can check out?

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Thank you, Trixter! I don’t have an illustrious POST card, (didn’t realize they even existed!) but I’ll cozy up to the maintenance manual and hopefully report back with progress!
 
the monitor should NOT be green like that, all my 25's have a black screen (both b&W and color)

It looks like a hardware failure either in the crt potion or in the video card. IBM is pretty good about having on-screen error codes, and if you solve the green crt issue, it might be telling you about the error as to why its not booting.
 
Thank you, luckybob! That's sort of what I'm afraid of ... I feel like the CRT is beyond my abilities to remedy and I'm not optimistic about scouring for a replacement motherboard, though I suppose that might be the lesser of the two evils?
 
Also—not sure where the angry emoji is coming from, I appreciate everyone's feedback so apologies on that slipping in there!
 
As far as my own personal knowledge with fixing CRT screens, i'd classify my self in the category of 'knows enough to be dangerous".

If I were in your position, i'd isolate the fault first. if you unplug the monitor from the motherboard and turn on the pc, does the image change? If the screen stays black, it would lead me to troubleshoot the monitor. If the screen remains green, I'd start to troubleshoot the crt.

In addition, you can make your own 2x5 header -> vga cable adapter. one of the members here has done it, and made a video about the process. https://www.youtube.com/watch?v=KjnbSpuq90I I don't recall exactly which member he is here, but hopefully he will be kind enough to chime in. Worst case scenario, just search this site, it should come up.

In most cases with the CRT, its bad caps that cause things to go all cactus. The fact the screen still comes up green, to me, is a good thing. It means the high voltage is working, and I'd wager the issue is in the "low" voltage side of the CRT. (if it is indeed the CRT).

As for troubleshooting the motherboard (if it is the cause), check the easy stuff first. Is the power supply supplying the proper voltages? (while under load) re-seat all the parts you can, look for obvious broken parts.
 
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luckybob said:
In addition, you can make your own 2x5 header -> vga cable adapter. one of the members here has done it, and made a video about the process. https://www.youtube.com/watch?v=KjnbSpuq90I I don't recall exactly which member he is here, but hopefully he will be kind enough to chime in. Worst case scenario, just search this site, it should come up.
Click to expand...

That would be me. ;)

My Model 25 has randomly started doing this actually itself, WITH a VGA card mind you (and grey because it's a black and white model). So far I've pointed at least my particular issue to the power good signal not going high, indicating some PSU issues. If you have a multimeter check the power connector for power good, that will be pin 1. If it's not that though, it could be a number of things and as mentioned a POST card would be needed since you're not getting any video output.
 
Thanks again, everyone! Unfortunately, I came down with COVID right after this posting, and have been ill ever since (yay for being a long hauler). Anyways, I didn’t want to just ghost, I’m still intending to get this guy back up and running! It’s in such great condition to just be sitting, so I’ll report back as stamina allows. Thank you again to everyone, stay tuned!
 
bushidounohana said:
Thanks again, everyone! Unfortunately, I came down with COVID right after this posting, and have been ill ever since (yay for being a long hauler). Anyways, I didn’t want to just ghost, I’m still intending to get this guy back up and running! It’s in such great condition to just be sitting, so I’ll report back as stamina allows. Thank you again to everyone, stay tuned!
Click to expand...
For the 'POST card' mentioned above, there is an easier option: A parallel port POST code reader. That is going to help to know whether the planar itself is functioning at some level.

There's a link to an unaffiliated eBay listing in the video description:
 
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