VOGONS


First post, by Durandal

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Hey all. I was recently given an IBM model 8503-004 monochrome VGA monitor but the VGA cable has been cut. Would anyone happen to have this same monitor and be able to open theirs up? It would be very simple to figure out the pinout - the cable connects inside to the neck board and mainboard using 2 sockets, you would just have to use a multimeter in continuity mode to figure out which wire goes to which pin on the VGA connector.

If not, does anybody have a service manual or schematic for the monitor?

Here are some photos so you have a better idea of what I'm talking about:
https://imgur.com/a/Q8Vt7uJ

Hoping somebody can help me out on this. I'd love to be able to use the monitor with my IBM PS/55! 😊

Regards,
Durandal

Last edited by Durandal on 2019-08-27, 07:16. Edited 2 times in total.

Reply 1 of 7, by dkarguth

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Based upon a VGA pinout I've found on the internet and the silkscreen on the board, the pinout appears to be this:

5 pin connector, from the left side of the picture to the right:
HS (white wire) - Horizontal Sync, VGA pin 13
VS (yellow wire) - Vertical Sync, VGA pin 14
SC (thin black wire) - See below
GR (thick black wire) - Ground, VGA pin 6
?T (brown wire) - See below

The last two pins on that connector are ID bit 1 and Sync Return. On a monochrome monitor, ID bit 1 is connected to ground. Ohm those pins out, and whichever one has continuity to ground is the ID bit 1!

ID bit 1 is pin 12 on the VGA connector, and Sync Return is pin 10.

3 pin connector, from left to right:
G (thick black wire) - Ground, VGA pin 8
Video/P (thin white wire) - Green signal, VGA pin 2
G (thick white wire) - Green signal shield, VAG pin 7

Sources used:

https://blogs.uoregon.edu/projectiondesignpdw … ga-information/
VGA-Pinouts-16fe4wk.png

https://cfusion.com/parts/index/REF_IBM_8503-001.html
REF%20IBM%208503-001%207.jpg

This website has more pinout information, including the ID bit codes.
https://pdos.csail.mit.edu/6.828/2017/reading … adoc/PINOUT.TXT

"And remember, this fix is only temporary, unless it works." -Red Green

Reply 2 of 7, by Durandal

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dkarguth wrote:
Based upon a VGA pinout I've found on the internet and the silkscreen on the board, the pinout appears to be this: […]
Show full quote

Based upon a VGA pinout I've found on the internet and the silkscreen on the board, the pinout appears to be this:

5 pin connector, from the left side of the picture to the right:
HS (white wire) - Horizontal Sync, VGA pin 13
VS (yellow wire) - Vertical Sync, VGA pin 14
SC (thin black wire) - See below
GR (thick black wire) - Ground, VGA pin 6
?T (brown wire) - See below

The last two pins on that connector are ID bit 1 and Sync Return. On a monochrome monitor, ID bit 1 is connected to ground. Ohm those pins out, and whichever one has continuity to ground is the ID bit 1!

ID bit 1 is pin 12 on the VGA connector, and Sync Return is pin 10.

3 pin connector, from left to right:
G (thick black wire) - Ground, VGA pin 8
Video/P (thin white wire) - Green signal, VGA pin 2
G (thick white wire) - Green signal shield, VAG pin 7

Sources used:

https://blogs.uoregon.edu/projectiondesignpdw … ga-information/
VGA-Pinouts-16fe4wk.png

https://cfusion.com/parts/index/REF_IBM_8503-001.html
REF%20IBM%208503-001%207.jpg

This website has more pinout information, including the ID bit codes.
https://pdos.csail.mit.edu/6.828/2017/reading … adoc/PINOUT.TXT

Thank you for this EXCELLENT response! And so fast too, I've been waiting for help elsewhere for a while... I should be able to try this out tomorrow and will provide an update post.

Reply 4 of 7, by Durandal

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dkarguth wrote:

No problem, always happy to help! Besides, I love a good puzzle. 🤣

Thanks to your help, I got it to work! And then it promptly stopped working... the image pretty much flickered out and disappeared entirely a few minutes after I finished soldering the wire and tested it for the first time. I quadruple checked my wiring and even re-soldered a totally different VGA cable to it, but it still isn't working anymore. The tube seems fine since I get flickering when I plug it into the PC I was testing with, and the brightness and contrast controls yield results, but no image at all. Oh well, into a $0.99 eBay auction it goes I guess!

Reply 5 of 7, by dkarguth

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This is a little late, but that sounds like bad caps. If you still have the monitor, and possess some soldering skills, you should open it up and see if there are any obviously bad capacitors. Be careful to discharge the caps before handling them, however, as they can hold a lethal shock.

"And remember, this fix is only temporary, unless it works." -Red Green

Reply 6 of 7, by Durandal

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dkarguth wrote:

This is a little late, but that sounds like bad caps. If you still have the monitor, and possess some soldering skills, you should open it up and see if there are any obviously bad capacitors. Be careful to discharge the caps before handling them, however, as they can hold a lethal shock.

I got fed up and shelved it... until yesterday when I gained some confidence from fixing an IBM 4707 E01 9" monochrome SVGA CRT by simply replacing a fuse. I dug out the 8503, re-examined your post, re-drew my wiring diagram and gave it a shot. It took me far longer than I'd like to admit (this sort of thing confuses the hell out of me), but to my surprise:

50XJV9t.jpg
P2sj6hK.jpg
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It worked! Here's how I wired it:

5-pin connector:
Yellow (VSync) --> VGA pin 14
White (HSync) --> VGA pin 13
Silver shielding (ground) --> VGA pin 5

3-pin connector:
Thin white wire (green signal) --> VGA pin 2
Thick white wire (green shield) --> VGA pin 7

And then I just cut the unused wires and sealed everything with heat-shrink tubing to make sure there weren't any shorts.

Aa01kYg.jpg

There's a pic of it with my new teeny tiny Flytech Technology Carry-1 12MHz 80286 PC. Thanks again for the info, I couldn't have done it without you. 😁

Last edited by Durandal on 2019-08-27, 07:16. Edited 1 time in total.

Reply 7 of 7, by Caluser2000

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Well done.

There's a glitch in the matrix.
A founding member of the 286 appreciation society.
Apparently 32-bit is dead and nobody likes P4s.
Of course, as always, I'm open to correction...😉