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IBM XT CGA to composite (or VGA, or S-video...) ?

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giobbi

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Hi all,

I recently got an IBM XT but I haven't its own monitor here with me (yet).

it has an AST ColorGraphPlus video adapter (that should be CGA, I suppose). It mounts the 6845 CRTC and has CGA and LPT connectors (at least my memory is suggesting in the 80s they used to merge lpt and video output on the same card...)

Since the XT probably isn't working for some reason, but I have the CRT to prove it, I was wondering if there's a way to make (i.e.) a CGA -> Composite adapter to connect it to a modern LCD Tv or monitor.

Surprisingly, I cannot find anything on google about that, just some dubious CGA -> VGA adapter for sale.

Is it possible to make that, and how?

thank you

--Giovi
 
Most of the CGA cards have composite video output (60Hz NTSC 3.58MHz) via cinch type connector. You can connect it via direct cable to video-in (usually yellow) cinch on the TV set. Alternatively if the TV has SCART connector you can use it with a very cheap and simple passive connector adapter that in turn provides cinch-type video input connector. If your TV supports NTSC 3.58MHz most likely you'll have a colorful picture.
 
I have two short CGA/LPT cards that have no composite out. That said I would be interested too in a TTL->Composite adapter
 
george said:
Most of the CGA cards have composite video output (60Hz NTSC 3.58MHz) via cinch type connector. You can connect it via direct cable to video-in (usually yellow) cinch on the TV set. Alternatively if the TV has SCART connector you can use it with a very cheap and simple passive connector adapter that in turn provides cinch-type video input connector. If your TV supports NTSC 3.58MHz most likely you'll have a colorful picture.
Click to expand...


It would be too easy :)
The card has two connectors only, the CGA (DE9 female) and the LPT (DB25 female).
 
archeocomp said:
I have two short CGA/LPT cards that have no composite out. That said I would be interested too in a TTL->Composite adapter
Click to expand...
You'd better buy one with composite out on ebay . B/W composite signal can be made with IRGB resistor matrix plus some TTL triggers to create proper composite sync pulse from V&H sync pulses. But the effort is meaningless.
 
george said:
You'd better buy one with composite out on ebay . B/W composite signal can be made with IRGB resistor matrix plus some TTL triggers to create proper composite sync pulse from V&H sync pulses. But the effort is meaningless.
Click to expand...

yes but they're quite expensive and I'm not even sure if they'll work...
 
Some CGA cards had composite video on pin 7.
I remember selling some adapters that had db9 on one side and a female composite on the other end.


Later,
dabone
 
Thank you all for your replies.

I found this site: http://www.seasip.info/VintagePC/cga.html where it's shown a card similar, for some aspects, with mine. although mine card hasn't the composite out, the author mentions the P1 composite header. My card has it, and the pin 3 is connected to pin 7 of the CGA connector.

However I checked it with my multimeter, and there's no output (not even the +12v on the pin 1).

I didn't try to connect it to a composite output (yet), but I'm suspecting something on the MB (maybe) isn't working. I checked the voltages; I have the +5 and +12 on the FDD and HDD power connectors, and some voltage on the MB connector; however I don't know the right voltages of this era PSU; can I use an AT power source (like one from a 486) ? In other words, if the PSU has a suitable connector, should it supply a right power/voltage?

I don't know (I don't remember!) what to expect as an usual behavior; should the speaker beep during start-up? Should the HDD led blink?

I'm a little rusty with these old dinosaurs (I was a teenager when I used to write programs on them!) and I don't know what to do in order to bring it back to life....


-- Giovi
 
I would pull out the CGA card and put in a VGA card. Then you can use just about any monitor to test it. If you can't find an 8-bit VGA card, most 16-bit ISA VGA cards will work.
 
Hmm, according to the little bit of info out there, the AST ColorGraphPlus can apparently display 320*200*16 color graphics when used with the right software. Very interesting card there.
 
Plasma said:
I would pull out the CGA card and put in a VGA card. Then you can use just about any monitor to test it. If you can't find an 8-bit VGA card, most 16-bit ISA VGA cards will work.
Click to expand...

It would be a good, and maybe I will choose to do that. But in first I wish to be sure the PC is working; I don't want to waste 40 euros for a vintage 8 bit VGA card if I'm not sure it will work (of course admitting the problem isn't the CGA card!).

I absolutely need some kind of approach in order to get the rid of it....

--Giovi
 
SomeGuy said:
Hmm, according to the little bit of info out there, the AST ColorGraphPlus can apparently display 320*200*16 color graphics when used with the right software. Very interesting card there.
Click to expand...

I tried to find some info on this card but, since I found nothing, it seems your Google skills are better than mine :)
 
Great Hierophant said:
The Soviets were really efficient in copying the CGA card, even that portion of the card, the NTSC composite video signal that would probably never have been used in a SECAM country.
Click to expand...
In this case not soviets but bulgarians did that. There were many imported TV sets that supported NTSC so that system was useful too. Actually the french SECAM was never used for a monitor signal since it has many artifacts and awful colour resolution.
 
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