CTM640/CTM644 SCART INPUT

pacomix · 16:21, 25 February 20

Hi everybody! After a long time without posting here I go. I have been recently trying to attach a SCART/EUROCONECTOR to my CTM64X monitor (CM14 will come) so I can connect any RGB + SYNC to it and the first attempt, as usual, went wrong.

With a Spectrum +3 scart I get a distorted image and no white color. Would that be a matter of just only adjusting the H-SYNC internally?

With a CPC464 using a tested and working SCART cable I get a stable image and right colors but they are really dark.

I have connected only the RGB SYNC and GND to the respective pins in the SCART female connector and I left the LUMINANCE pin disconnected. Is that the right approach or should I perform something else?

I have been thinking about it a bit. The SCART cable coming from the +3 and the CPC464 has resistors attached as stated in several places. Could there be the possibility that the CTM has already these resistors in the PCB of the monitor in the RGB and SYNC signals?

Any help will be appreciated. Thanks!

I will keep you posted with the CM14 attempt.

Bryce · 09:28, 26 February 20

Definitely remove the resistors, they aren't needed on the CTM.

Bryce.

pacomix · 13:58, 26 February 20

I was thinking it was the origin of the problem. I guess the best thing to do in order to be flexible when connecting all kind of SCART sources to any RGB monitors (not only CTM/CM) is to have a small connection box with variable resistors on each line.

@bryce do you know if there is such device somewhere?

Bryce · 14:02, 26 February 20

You'd have to make it yourself, but I doubt you would ever need it. The resistors in the cable are there to lower the levels going to a standard SCART input, which is expecting lower levels than the computer puts out, but CTM isn't a standard SCART device, so if anything you would probably need to amplify the signal if you connected a real SCART device to the CTM, not reduce it.

Bryce.

pacomix · 19:30, 26 February 20

Thanks for your always helpful explanation Bryce.

I cooked today the adaptor for the CM14 and I attached my MSX2 through a fully wired standard SCART cable (no resistors) to both with similar results. This time I think the problem is somehow the horizontal sync.

I managed to leave the vsync stable after touching the vhold knob though. Any clue?

Quote from: Bryce on 14:02, 26 February 20
You'd have to make it yourself, but I doubt you would ever need it. The resistors in the cable are there to lower the levels going to a standard SCART input, which is expecting lower levels than the computer puts out, but CTM isn't a standard SCART device, so if anything you would probably need to amplify the signal if you connected a real SCART device to the CTM, not reduce it.

I don't plan to connect any other devices to the monitor other than retro computers so I think I don't need to amplify anything but this box with variable resistors was intended to avoid having different SCART cables for TVs and monitors.

pacomix · 21:24, 26 February 20

@Bryce I updated my last post with pictures. Any help will be more than welcomed!

Fessor · 23:06, 26 February 20

According to this thread, a 70ohm resistor should be connected between sync and gnd
https://www.msx.org/pt-br/node/8440

Bryce · 08:18, 27 February 20

Yes, it's not catching the sync signal. Unfortunately, I don't know what the sync signal of an MSX looks like, so it's difficult to give advice. Make sure the GND of both the MSX and the CTM are at the same level (ie: a good connection between the GND in the computer and monitor) and if that doesn't help, then you could try pulling it lower as Fessor suggests above.

Bryce.

pacomix · 11:52, 27 February 20

I thought that just adding a SCART female connector and a point-to-point SCART cable would make any standard RGB + SYNC device work out of the box but I see this is not really true...

I'm a bit surprised since my old CM8833 displays fine all of my computers without having to mess with resistors/capacitors...

Thank you very much for all the support!

BSC · 14:22, 25 February 23

Hi peeps,

I want to connect my SNES with an existing Scart-RGB-cable to my CTM-644 monitor and I discovered those two offers (I am sure there are more if I keep digging):

http://retrocables.es/tienda/index.php?id_product=18&controller=product&id_lang=1#idTab5

https://coolnovelties.co.uk/coolnovelties/amstrad-video-cables/26-amstrad-ctm-644-monitor-rgb-scart-adapter-0705693505299.html

Has anybody bought any of those and can tell me if they worked for that purpose? I am thinking of ordering
at retrocables.es for the price and the fact that Spain is in the EU ..

TotO · 14:33, 25 February 23

What I think is a lot of electronic is missing compared to a TV to connect others system to a CPC or Plus monitor through RGB. It can works with a simple cable, but the luminosity will be probably not good and can't be adjusted. The best it to use the MP-3 module.

BSC · 16:27, 27 February 23

Quote from: TotO on 14:33, 25 February 23What I think is a lot of electronic is missing compared to a TV to connect others system to a CPC or Plus monitor through RGB. It can works with a simple cable, but the luminosity will be probably not good and can't be adjusted. The best it to use the MP-3 module.

I am not sure if I understand your response. Are you saying that the display will be dimmer than it should be when using any Scart-Cable?

TotO · 16:36, 27 February 23

Quote from: BSC on 16:27, 27 February 23I am not sure if I understand your response. Are you saying that the display will be dimmer than it should be when using any Scart-Cable?

I mean, the CTM was designed to boost the Gate Array RGB signals and to remotely adjust its luminosity. If you directly connect a SNES or a Mega Drive through a simple cable adapter, the display will be probably saturated and the luminosity can't be adjusted.

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CTM640/CTM644 SCART INPUT