PDA

View Full Version : Olivetti M240 CGA composite with mono composite monitor



AlexC
September 8th, 2017, 06:05 AM
I'm not sure if what I'm trying to achieve is possible and my search-fu isn't optimal today. So...

Olivetti M240 monitor with OGC / CGA card, composite output connected to Olivetti amber monochrome CGA monitor. Works fine for 40- or 80-column text and CGA graphics.

Olivetti Prodest MM 1200 green composite monitor with RCA input. When connected to the above system it shows a distorted image broken up across the screen so it's effectively showing four narrow columns of the source image, but badly broken. This is true regardless of screen mode.

I'm guessing the Prodest monitor will work with old console-type computers such as BBC Micro (it came with a clone of the Master, I think), but not with a CGA composite source. Is there anything I can do to change that?

Alternatively, the Prodest monitor could be broken. Since I have nothing else to test it with at the moment, I can't be sure. Or the RCA cable I'm using might be of a poor quality. I've ordered a coax one but I don't think that'll make a difference.

Any ideas?

tipc
September 8th, 2017, 07:05 AM
Are there any external adjustments? Composite is composite, usually, rare exceptions. Sounds like it should be compatible. In any event if it is defective it's probably just a minor component. Hopefully. Please don't chuck it, in Germany of all places I'm sure you could find tons of tinkerers.

1ST1
September 11th, 2017, 11:20 AM
Hello, the M240 has the same DB 25 pin female video connectpor like Olivetti M24 and AT&T 6300. You can find analogue RGB plus H/V-Sync signals on there. (there is also +12V to power Olivetti's proprietary monochrome monitors)

You should be able to find it's pinout here or there:
- https://sites.google.com/site/att6300shrine/Home/downloads
- http://www.olivettim24.hadesnet.org/doc.html

1ST1
September 16th, 2017, 12:21 AM
Composite video is a single coax signal. It's also called FBAS. It's the same signal like Commodore 64 and Atari ST and Amiga has on a chinch connector or within the video connector (Atari ST and Amiga also have RGB). Also some SCART connectors have composite video signal. You maybe also know it from video recorders, video cameras, dvd playsers, there you have a three chinch connector cable with yellow, red and white connector, where red and white connector are stereo audio and yellow chinch is composite. Also the original IBM CGA card has a composite video output, that is what @Trixter uses for his display tricks in the 8088MPH demo to get some effects. This because video bandwith of composite is lower than CGA and all CGA signals are put to gether in one signal what means some quality loss, that basically is what Trixter uses in his demo to get effects.

See https://en.wikipedia.org/wiki/Composite_video

To complete my statement above, the RGB+H/V-Sync signal which M24 puts out, signalwise it is compatible with VGA, so most VGA monitors and displays can display it (maybe the video timing is a bit different for some monitors).

AlexC
September 16th, 2017, 08:29 AM
Thanks, guys. I've tried the monitor's adjustments but there are none for the card that I can see. I tried changing the motherboard switches for different installed cards but that made no useful difference.

The card has both DB25 and composite connections but I wasn't sure if composite was always composite. Sounds like it is, so I'll test with another machine I should have next week, which I know works properly with composite monitors. The coax RCA cable made no difference.

AlexC
September 17th, 2017, 02:07 AM
Today I tested the green phosphor Prodest monitor with the CGA composite output of a Commodore PC10-III and it works just fine. I've no idea why it doesn't work with the Olivetti PC's CGA/OGC card, but it's no big deal. At least I know the monitor is good.

Chuck(G)
September 17th, 2017, 09:15 AM
I'm having a little trouble understanding this thread. The Olivetti MM 1200 is a 15KHz (http://retrocomputing.altervista.org/macchine/pc128s/mm-1200-3.jpg) monitor; the output of the M24/240 is closer to EGA frequencies, which explains the image breakup.

AlexC
September 17th, 2017, 09:36 AM
I'm having a little trouble understanding this thread. The Olivetti MM 1200 is a 15KHz (http://retrocomputing.altervista.org/macchine/pc128s/mm-1200-3.jpg) monitor; the output of the M24/240 is closer to EGA frequencies, which explains the image breakup.

To summarise:

My M240 is equipped with an Olivetti OGC card which I believe is 'CGA plus some extra modes' and is attached to an Olivetti amber monochrome monitor via a composite/RCA cable. Connecting the Prodest composite monitor to that output doesn't work, even though the Prodest monitor *does* work with the composite CGA output from a Commodore PC10-III.

So it appears that either not all composite outputs are the same - which I didn't know and apparently I'm not alone in that - or the OGC card is doing something unusual but using an RCA connector to do so. Given that pretty much every connector on the M240 is non-standard, that wouldn't be surprising either.

But it's OK because at least I know the Prodest monitor works.

1ST1
September 17th, 2017, 09:59 AM
Do you have a Prodest PC1? I have, but no original monitor. I run the PC1 via RGB digital on NEC Multisync or RGB analogue on a Philips Monitor which is compatibe to ATARI ST and Commodore Amiga color modes (PAL).

AlexC
September 17th, 2017, 10:24 AM
Do you have a Prodest PC1? I have, but no original monitor. I run the PC1 via RGB digital on NEC Multisync or RGB analogue on a Philips Monitor which is compatibe to ATARI ST and Commodore Amiga color modes (PAL).

No, I don't. Would you be interested in buying my green-phosphor MM 1200? I'm not sure I'm going to need it now. PM me if so.

And to complete the puzzle, the amber Olivetti monitor definitely does *not* work with the CGA composite output from the Commodore PC10-III. So, same connector but different signals. I learn something new every day...

Touchme
September 27th, 2017, 10:32 AM
I'm not sure if what I'm trying to achieve is possible and my search-fu isn't optimal today. So...

Olivetti M240 monitor with OGC / CGA card, composite output connected to Olivetti amber monochrome CGA monitor. Works fine for 40- or 80-column text and CGA graphics.

Olivetti Prodest MM 1200 green composite monitor with RCA input. When connected to the above system it shows a distorted image broken up across the screen so it's effectively showing four narrow columns of the source image, but badly broken. This is true regardless of screen mode.

I'm guessing the Prodest monitor will work with old console-type computers such as BBC Micro (it came with a clone of the Master, I think), but not with a CGA composite source. Is there anything I can do to change that?

Alternatively, the Prodest monitor could be broken. Since I have nothing else to test it with at the moment, I can't be sure. Or the RCA cable I'm using might be of a poor quality. I've ordered a coax one but I don't think that'll make a difference.

Any ideas?

Sure, the coax may not be that handy in such a case. I ever tried adjusting the monitor and the motherboard to no avail. Would you mind a touch screen from https://comparily.com/best-touch-screen-monitor/ .Well, I'm asking because I got one from there and it's superb. Actually, I run it via RGB analogue and it's amazing.