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IBM 8503 Monochrome VGA Monitor - Cut VGA cable, need help wiring a new one.

J

Joudan

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Apr 15, 2018
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Hey all, I was recently given an IBM 8503-003 (200 - 240V version, US version is 001 I believe) monochrome VGA CRT. Unfortunately the VGA cable was cut off on the outside at some point and I can't find a service manual or schematic for this monitor online. I opened it up to see where the VGA cable connects internally and it goes to the main board and neck board, here are some photos of the connectors and cable:

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5.jpg

I have an IBM 4707 E01 monochrome VGA CRT which I assumed might have a similar connector inside, and it doesn't. Anyone able to help?
 
Bump, any help? I can't edit the original post for some reason so I'll add here:

Does anybody own an 8503? I would be eternally grateful if you could open up your monitor and use a multimeter in continuity mode to map the pinout of the VGA connector, it would only take you a few minutes. ;-)
 
Well, even with no data from what I can see you can start to narrow it down. The white wire is likely the H sync, the yellow one the V sync. The thin black on the same connector is likely the sync (digital ground) ground and the thick black, the same as on the other 3 pin connector, the signal and main ground most likely.

The interesting thing here, is you say its a VGA monochrome monitor, but looking at the 3 pin signal connector (the outer two terminals are grounds, one for the coax), the central connector is a single wire, not the R ,G and B signals of VGA. So this implies one of two things; they have just used say the green channel of the VGA signal to drive the monitor, but more likely, hidden inside the old plug that was cut off, there is a matrix of 4 resistors that mix the R,G & B signals in the correct proportions to make the single "monochrome" video signal that is fed to the center of that 3 pin connector. All of this, just guessing from the photos.I am uncertain about the brown wire on the 5 pin connector.
 
Hugo, I'm not so sure about that. If memory serves, two of the pins on the VGA connector identify the monitor as either color or monochrome (i.e. pin 11 NC, pin 12 gnd). Likely, there's only a single video signal.

See the following discussion here
 
Chuck(G) said:
Hugo, I'm not so sure about that. If memory serves, two of the pins on the VGA connector identify the monitor as either color or monochrome (i.e. pin 11 NC, pin 12 gnd). Likely, there's only a single video signal.

See the following discussion here
Click to expand...

So it was pretty well what I had guessed and its just the green signal used for the video. That really surprises me though because if you have a VGA graphic image (rather than text) it could look awful on a monochrome monitor without a proper grey scale as R & B is missing. If I was using a monochrome monitor on a VGA output I would mix the three colors in the correct proportions, much like can be done done with CGA, to generate a monochrome signal with a reasonable grey scale.
 
That's not really possible with a monochrome jug. Monochrome VGA has only 64 grey levels--the eye can't really discern more than that.

One occasional thing that I remember with early (CRT) VGA, it was sometimes possible for the adapter to boot in monochrome mode. I believe that the same signal was sent to all (RGB) pins in that case.
 
I'm sure that's the way it works. The solution was usually to re-seat the VGA connector. You can try it yourself. It should be pretty simple to change the ID pins.
 
A very late update to this, but somebody on vogons gave me a great pinout and I managed to get it working. For anybody else who needs 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

Aa01kYg.jpg
 
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