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VGA and EGA display - no connectors - what to do ?

Sandisk78

Experienced Member
Joined
Apr 2, 2016
Messages
111
Location
Moscow, Russia
Hi, people ! I have two displays - EGA (called Cortan - works with EGA and CGA) and VGA - early 90's VGA - thay have no connectors - they were cut by vandals - is it possible to pick the combination of the cables running into it, without burning them or it's hopeless ?
 

justanotherhacker

Experienced Member
Joined
Mar 22, 2013
Messages
72
Location
London, UK
Hi,

what a shame! sorry to hear it. Definitely NOT hopeless though. All depends on your electronics confidence but it's nearly always worth at least a basic investigation before giving up. Personally I would try it.

EGA and VGA work a bit differently so I'm not sure there can be a universal rule here. Unfortunately as far as I know there is no absolutely standard colour code for VGA wires. (no idea for EGA). I assume you don't have the existing one. However...

- EGA is simpler and ought to be easier
- it's worth taking the backs of the cases off (if they have been powered up recently they can retain dangerous voltages, but if not they are usually fine) and looking at where the wires go into the board, because sometimes the wire attachment points have names/labels (in which case it's straightforward to fit a new cable) and sometimes they have an arrangement that is easy to relate to the plug arrangement (ie same shape, or are in a line numbered 1..9 or 1..15 which corresponds to the pin numbering). Only if you have NONE of this info do you start needing to trace where things go on the circuit.
- it's usually easy to identify the ground wire and that can help you decipher the rest (because you know which pin it's meant to be)
- identifying which wires are the synch wires and which is which is pretty critical. If you swap over a colour the result is weird but not likely to cause burning :)
- sometimes the main r, g, b wires on VGA are a different wire type than the others (with their own screening)
- sometimes r, g, b wires have corresponding colour codes (eg I've seen cables where they're all white with a stripe of the relevant colour) which makes it a bit easier
- I have no direct experience of EGA, only CGA and VGA. However it looks like EGA ONLY has ground, h and v sync, and digital colour signals so as long as you can find the ground and sort the sync out, the remaining pins are sending comparable signals
- VGA has both analogue signals (for the picture) and digital (for variations around digital identification/communication of setting info with the card) so there are quite a few more things going on on the VGA cable and it may be harder to figure out. The one time I had to worry about this I was lucky and the arrangement of the board made it clear.

Good luck!
 

Valerio

Experienced Member
Joined
Aug 20, 2017
Messages
131
Location
New York, Rome, London
At least the VGA one I think should be doable. Once you eliminate the wires that are a dead short to ground, look for those that have a ~75ohm resistance to ground - these should be the colour lines. The rest are TTL so anything with a high impedance to ground should be safe to connect to H & V from the video card. Then trial and error!
 

Sandisk78

Experienced Member
Joined
Apr 2, 2016
Messages
111
Location
Moscow, Russia
thanks for the advice ! on EGA workers by mistakes damaged the connector while rebulding our appartment and on the VGA the data cable was lost on a computer expo - it went by mistake to another town - as the retrocomputer event was organised by people from St Pete, while I'm in Moscow, Russia.
 
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