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giobbi
November 19th, 2013, 09:54 AM
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

Tronix
November 19th, 2013, 10:07 AM
I'm not sure but you can try this http://www.electroschematics.com/377/cga-scart-adapter/

george
November 19th, 2013, 10:09 AM
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.

archeocomp
November 19th, 2013, 10:26 AM
I have two short CGA/LPT cards that have no composite out. That said I would be interested too in a TTL->Composite adapter

giobbi
November 19th, 2013, 10:37 AM
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.


It would be too easy :-)
The card has two connectors only, the CGA (DE9 female) and the LPT (DB25 female).

george
November 19th, 2013, 10:38 AM
I have two short CGA/LPT cards that have no composite out. That said I would be interested too in a TTL->Composite adapter
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.

giobbi
November 19th, 2013, 11:01 AM
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.

yes but they're quite expensive and I'm not even sure if they'll work...

dabone
November 19th, 2013, 11:36 AM
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

george
November 19th, 2013, 01:48 PM
yes but they're quite expensive and I'm not even sure if they'll work...

Cheap and they worked:
http://www.ebay.com/itm/261320012720
http://www.ebay.com/itm/261320016690

Great Hierophant
November 19th, 2013, 02:27 PM
Cheap and they worked:
http://www.ebay.com/itm/261320012720
http://www.ebay.com/itm/261320016690

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.

giobbi
November 19th, 2013, 03:36 PM
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

Plasma
November 19th, 2013, 03:46 PM
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.

SomeGuy
November 19th, 2013, 03:56 PM
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.

giobbi
November 19th, 2013, 04:09 PM
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.

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

giobbi
November 19th, 2013, 04:11 PM
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.

I tried to find some info on this card but, since I found nothing, it seems your Google skills are better than mine :-)

SomeGuy
November 19th, 2013, 05:22 PM
A lot of stuff on uncommon vintage parts only turns up if you select Google's "books" search:
http://books.google.com/books?id=NFT964jBihIC&pg=PA52&dq=AST+ColorGraphPlus&hl=en&sa=X&ei=XByMUpyNLciokQfhsYHYCw&ved=0CB8Q6AEwAA#v=onepage&q=AST%20ColorGraphPlus&f=false

Caluser2000
November 19th, 2013, 09:40 PM
There is info in Hardware wiki about 8 bit compatible VGA cards.

george
November 20th, 2013, 12:13 AM
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.
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.

giobbi
November 20th, 2013, 04:45 AM
A lot of stuff on uncommon vintage parts only turns up if you select Google's "books" search:
http://books.google.com/books?id=NFT964jBihIC&pg=PA52&dq=AST+ColorGraphPlus&hl=en&sa=X&ei=XByMUpyNLciokQfhsYHYCw&ved=0CB8Q6AEwAA#v=onepage&q=AST%20ColorGraphPlus&f=false

thank you, I didn't think at it :-)

angel_grig
November 20th, 2013, 06:09 AM
You can also try the chinese converters like this one http://www.ebay.com/itm/New-Arcade-game-RGB-CGA-EGA-YUV-To-VGA-HD-Video-Converter-Board-GBS8200-/190881473083?pt=LH_DefaultDomain_0&hash=item2c716c223b or you can make a CGA to scart converter see here http://www.vintage-computer.com/vcforum/showthread.php?17610-CGA-to-SCART-adaptor (if you have a tv with scart input)

giobbi
November 20th, 2013, 06:37 AM
or you can make a CGA to scart converter see here http://www.vintage-computer.com/vcforum/showthread.php?17610-CGA-to-SCART-adaptor (if you have a tv with scart input)

That sounds fine, I will do a try, thank you!

btw I bought an 8 bit ISA VGA card for an outrageous price on eBay, but it will last >1 month to come here in Brazil (damn'd custom!). I will keep you informed!

--Giovi

giobbi
November 21st, 2013, 04:45 AM
You can also try the chinese converters like this one http://www.ebay.com/itm/New-Arcade-game-RGB-CGA-EGA-YUV-To-VGA-HD-Video-Converter-Board-GBS8200-/190881473083?pt=LH_DefaultDomain_0&hash=item2c716c223b or you can make a CGA to scart converter see here http://www.vintage-computer.com/vcforum/showthread.php?17610-CGA-to-SCART-adaptor (if you have a tv with scart input)

Ok just for future needs I bought at outrageous price an ISA, 8 bit VGA card on eBay.

However, thanks to the gentle soul (modem7) that told me about http://www.minuszerodegrees.net/ and thanks to the info and the troubleshooting on the site itself (terrific site!) I finally removed the two tantalum capacitors (C56 / C57) and my 5160 board resurrected.

So I decided to follow the Dabone tip and see if my CGA card has the composite output at pin 7. Since the card shown at this page: http://www.seasip.info/VintagePC/cga.html is quite similar to mine (even if mine has an LPT but not a composite out connector), I decided to draw the output from the P1 header.

It works, with some restrictions: the image seems to be B/W only (even if the MB switches are set as CGA 80x25) and it's a little plagued by some interferences (ok I'm not using a good cable, as you can see in these pictures). I tried to set the C1 variable capacitor, but it doesn't change anything.

But it was nice to discover the computer itself is working!

--Giovi

p.s. I was forgetting to post the pictures:

16054
The connector on the P1 header. green = GND at pin 4, white = composite signal at pin 3. Pin 2 = cut, Pin 1 = +12v

16055 16056
A couple of pictures of the small and cheap 5" LCD TV (with 16:9 ratio). It seems there's almost no difference switching among PAL, NTSC and SECAM; at least on this TV. Not very readable, though, but the image is really smaaaaaaaall.....

----------------------------------UPDATE

I discovered it retuns some kind of a color (blue) image on the composite output too, when I ran the "Strip Poker" game I found on the HD :-)
But other colors maybe don't work

----------------------------------SECOND UPDATE
It seems I can get some fine colors (ok, I mean fine CGA colors ;-) ) in graphic mode. I found here PacMan, IBM Cats and some moregames that worked in graphic resolution with colors; but I can't see the colors in 80x25 text mode. I eventually connected the composite out to an old NTSC 14" CRT TV. Not the best for my eyes :cool:, but it works....

modem7
November 21st, 2013, 09:39 PM
However, thanks to the gentle soul (modem7)
Gentle? Well, I don't know about that. There was that one time I swore in 1975 after dropping a hammer on my foot.


I finally removed the two tantalum capacitors (C56 / C57) and my 5160 board resurrected.
I have added your repair to the list at http://www.minuszerodegrees.net/vcf_motherboard_failure_history.htm


I eventually connected the composite out to an old NTSC 14" CRT TV. Not the best for my eyes , but it works....
Expected, because the composite output is NTSC.