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Cheapest way to display CGA

JonB

JonB

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Jan 26, 2014
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Hi

I have an Amstrad PPC640 and I'd like to use an external display, because its tiny "supertwist" LCD is utterly useless. The machine is equipped with an IBM compatible 9 pin CGA output and I would like to connect it to a (relatively) modern monitor. I'm hoping not to have to go looking for an old IBM monitor! I have a choice of analogue video via SCART (which I think is not going to work as the output is TTL digital) or standard VGA.

I guess the question is, can I get (or build) an adapter that will do the conversion? Do any of them actually work? I've seen simple things and others with PCBs having lots of surface mount components fitted (which make me wonder if conversion is non trivial).

Any ideas?
 
Analogue displays can handle digital signals, just not the other way round. I don't know much about SCART, but I think a PAL display would be close enough for CGA.
 
The Commodore 1084 is a great monitor that accepts RGBI video. There are different versions, with dsub9 or DIN connectors.
The commodore 1902A monitor also has a RGBI input with DIN connector
 
perhaps google CGA to composite (or PAL) converter. I believe it's relatively easy to convert disparate CGA signals into composite. More difficult the other way around.

Then you can use a tv set. You may have to fiddle w/the sync controls. If it is that PAL is that similar to American NTSC/Composite/RS-170 video.

But remember, even with the ideal circumstances of having composite video for your perusal and a ready to go American tv set, you still need to modulate that signal to be picked up by channel 3 or whatever, meaning you need a rf modulator. TV's don't accept composite video (yes more modern ones do I guess). O whatever.

Perhaps you can find an NTSC composite monitor somewhere for not too many pounds.
 
If you have SCART, I assume you are in Europe. As they don't (usually) have SCART in the USA most folks probably won't understand how useful it is. First you need to check which pins are implemented. Some TV's only implement composite on the SCART other implement RGB. Also CGA is US scan rates check it will handle those as well. Almost all modern i.e. flat panel TVs will cope with both those requirements. If it will handle RGB and US scan rates then you can use a simple converter. The issue with CGA is that it is RGB + Intensity. So you need to change the levels of all three RGB lines when the intensity line is set. This can be a little complex, but not expensive. This one looks really first class:-

http://gamesx.com/wiki/doku.php?id=av:g7000_av

A simpler adaptor is here, with pics of it being used with a PPC

http://www.retrowiki.es/fororw/viewtopic.php?f=700&t=31814

probably worth just knocking one up one of the second ones and just trying.
 
KC9UDX said:
Which one would that be?
Click to expand...

On my turbo 8088 XT I just use a Commodore 1084S, and grabbed a Commodore 128 CGA cable off ebay (new)
If it supports TTL, it'll have a small push button to enable it. Some models have even have a 9 pin plug, mine was just the usual DIN though.

Contrast isn't as good as an IBM 5153, but does CGA just fine.
 
The simple CGA->SCART adaptors seem to be a bit hit and miss. Mine works OK with the LCD TV in my kitchen but not with an older CRT TV.
I have tried various other things too (e.g. Extron RGB 202xi) but wasn't happy, so I've bought an IBM 5153.
An Amiga monitor (e.g. 1084S, Philips CM8833) would be a good compromise as you can use it for other computers too.
 
There were many variations of 1084 and 1084S. I guess I never ran into one that supported TTL.
 
I think that CGA to SCART layout by "Unknown author" exists in a few variations. Worth noticing is that standard CGA does not have a 5V nor a 9V output to drive your MOSFET (?) or 74 series chip, so if you find a layout that connects that line to the DE9, it is specific for some computer using a custom CGA that has a such power source. I tried to build this one earlier this year but got zero output. At first I thought it was due to my bad soldering, but then I found another forum where this particular design was slaughtered as fake or relying on properties not part of standard CGA, so I'll chalk it down to that.

I haven't tried Fishfinger's design though, I suppose it works better. In any case, you seem to require an external 5V source to power your 74 series chip. The same goes for the design on the Spanish forum, remember to bring your own power source in order to combine the H and V sync to a C sync.
 
KC9UDX said:
There were many variations of 1084 and 1084S. I guess I never ran into one that supported TTL.
Click to expand...
The Commodore monitors were rebranded Phillips-Magnavox monitors. Sometimes the Magnavox versions also turn up. The Magnavox CM8505 has inputs for Composite, Analog RGB, and IBM compatible TTL RGB. It also has a switch to easily flip between composite and RGB inputs.

The easiest way to tell for sure is by looking at the back. You will see an RCA plug for audio, RCA for composite, a DIN plug for analog RGB, and a second DIN plug for TTL RGB.
 
SomeGuy said:
The Magnavox CM8505 has inputs for Composite, Analog RGB, and IBM compatible TTL RGB. It also has a switch to easily flip between composite and RGB inputs.
Click to expand...

Neither my CM8833 nor my 1084S could display CGA composite in colour though.
Probably because they are PAL models, not NTSC. They can handle the 60 Hz signal though, so you get a stable image, just in monochrome.
 
I had a Daewoo one, and one other, don't know what that one was.

I did have an earlier Commodore monitor (can't recall the model) that did have composite and RGBI.
 
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