Weird problem with CTM644 and Atari STs

[Gryzor]

Ok, here something that got me stumbled.


Atari 520ST+/specially-built cable/CTM644: perfect
6218 and CTM: perfect.
Atari 1040STe/specially-built cable (just got it)/CTM644: oh damn.


After a minute or less the picture starts caving from the left and soon after starts rolling violently:


[attach=2]


You'd think that the STe is at fault, but the problem appears only when the CTM gets warm. If I switch on the STe first and let it run for a while, then switch the CTM on, then the picture will be perfect for a minute. If I switch the CTM on first, let it run for a couple of minutes then switch the STe on, then the picture will be screwed from the start.


So... what? Could the cable be faulty and *somehow* be causing this? I got it from coolnovelties (nice chap)...

[Token]

It's a stand alone cable? (DIN ST to DIN CTM644)
I now use a MP3f with my 1040 STe or 520 STf and stock SCART lead cable. But I also have this adaptor (see link), and the signal is too hot for the CTM644-2. With the help of Bryce I added some resistors on the RGB lines. I don't know if it could be the problem...
Amstrad CTM-644 RGB Scart Adapter Cable

[Gryzor]

Yes, it's a standalone cable, DIN to DIN. Coolnovelties doesn't have it on the website any more though. Unfortunately I don't have a french MP3 (oh how I want one!)...

[Token]

The Atari ST signal was too hot with my RGB modded MP3f as well. I added a 3 ways SCART lead, put resistors on SCART input 3. I can use the Atari 800 XL and C64 on the CTM644, I connect a 9V battery on the other SCART input...


If you don't have to reduce the brightness pot to zero on the CTM, the cable have resistors...


Btw I also have a CTM644 old logo, there's even more brightness.

[Gryzor]

But this is not SCART

In any case, if it's the cable's problem, that's no biggie, I'll talk with Coolnovelties. I am just trying to figure out if it's the cable or something else...


[EDIT] Though the technicals are useful, and I'll send this thread to Coolnovelties to take a look...

[Gryzor]

Anyone?

[Token]

I wish Bryce can help on this...


You wrote "specially-built cable" on ST and STe, it's the same cable I think. But not sure.


Does the screen is dark when you turn down to min the brightness on the CTM644?


If you have a flashy white and green GEM screen even setted this way, that mean RGB signal is too hot, bad for the monitor.

[Gryzor]

No, you're right, I wasn't clear enough, but that's why I wrote "just got it" next to the second one. They're different cables.

The screen *is* a bit too bright indeed but the problem appears even if I turn it all the way down, when it's pretty dark (not as dark as on the CPC though; and not sure it'd help anyway?).

What do you mean by "flashy" screen?

Thanks man

[Token]

Ok, so you must have swapped the cables etc (or I didn't know the DIN pinouts could be different between all ST's, I use the same cable on my STf and STe)



Flashy, sorry, I meant a nice "usual" brightness.
If the picture get dark when you reduce the brightness it's a good thing. 
A too hot signal (from the cable) could reduce the life/damage the monitor... (even if you reduce the brightness pot)

[Gryzor]

Appears that this specific model, an early 520ST+ (not F, not M) is a bit different hence the special cable.

Thanks for the explanation. What I meant was, if I turn it down, where brightness is still higher than the usual "low" brightness but low enough, will that damage the monitor as well?

[Token]

Oh now I remember this rare ST, thank you
I think it's ok if you get a +/- dark picture.

[Gryzor]

Heheh...

Let me rephrase the question:

if you send a signal that's too "hot", where does the damage occur? If it's the tube that gets damaged than by turning down the brightness you could probably avoid it. But if it's some other component before that then even turning down the brightness won't prevent it.

Anyhow, could the initial problem I mentioned be caused by the cable after all?

[Token]

Yep, turning down the brightness on the CTM won't prevent the problem. Indeed it must be some component before the tube. (probably burn something on the PCB) but on this I can't help)


Reducing the brightness on the CTM was just a test to know if your cable reduce or not the signal coming from the Atari.
Picture is dark = good


Of course it is possible that it's not the cable...
Now we know that at least it's not the RGB line that are too hot, I though it could be the problem.

[Gryzor]

Just what I thought, thanks. Just one question - at the lowest brightness setting, how bright should the image be? I can try posting a picture of mine, which I believe is still too bright for that low level... are you supposed to be able to see things (on the CPC at the lowest level blue appears as black, for instance)?

I'll email this thread to CoolNovelties, they offer excellent support for which I'm very happy, and we'll see.

By the way: it appears that my ST+ cable actually works!!!!!! Picture probably still too bright, but heck, it doesn't roll! This is fun

[Token]

Oh that's nice news 


Don't take it as a law, I'm not an expert but I think at the same level of brightness on the monitor it should be like the CPC.


If it's really too much you should see it. With my SCART/DIN adaptor the picture is bright with brightness pot setted to zero.


I made a white and green background on the CPC (poor test I know) and I had to set the brightness pot to 90% to look similar.
I can't tell how it's dangerous for the monitor.


In fact I was thinking that your monitor could be tired and couldn't handle the ST signal like mine anymore. But as you can see it now, that new cable must have a simple soldering problem.


My SCART/DIN adapter wasn't sold as specific, it's for every SCART lead, sold as "working" also with the ST. So it's not a cable with built-in resistors.
Also the seller didn't wrote any warning about the brightness.


Monitor compatible - CPCWiki

[roy bates]

just take the working cable apart and see if it has resistors in it anywhere...and compare it to the one that dont work

[Bryce]

if you send a signal that's too "hot", where does the damage occur? If it's the tube that gets damaged than by turning down the brightness you could probably avoid it. But if it's some other component before that then even turning down the brightness won't prevent it.

By "too hot" you mean the voltage levels are a little bit too high. This won't damage anything in the monitor unless of course the voltages were pumped up above 12V or something crazy. It just makes the screen too bright and looses some clarity on brighter shades. STs are above the standard levels, so resistors are needed to bring the levels back down.

Bryce.

[Gryzor]

So we're talking just normal wear of the CRT due to higher levels, correct? (does such a thing even occur?)

[roy bates]

sorry i cant see any wear on your crt from the picture,the cable probably just needs resistors on the rgb signals to lower the strength of the signal from the atari

[Gryzor]

No, I was talking about long-term, rather

[Token]

It's nice info Bryce!
On my CTM644-2 the 1040 STe seems to have correct colors if I reduce the brightness to zero with the pot on the side. I think that since the RGB line levels aren't a problem for the monitor then adding resistors are more an option to get a probably more accurate picture or reduce the light a little more...


Lately I connected my MP-3f to a GBS8200. I had similar screwed fx on screen then I tried to turn the 2 pots on the MP-3f, setted to zero picture became stable but that did nothing on the colors. I did the test with an Amiga 500, quite a dark picture, so I'll make another cable.. (one 6 DIN for every machine could have been cool, use the MP3f front with the 8200, SCART box connected to the back to make an easier connexion)
Will test other computers, Atari ST, C64, XL will also tried RF signal VCS, mattel)
I also want to try to connect my C64 on the GT-64, but it failed, I hope you'll try it in the future

[roy bates]

i would imagine the resistors need to be around 100 ohm in series on the rgb signals.or there abouts.
which would probably fix the brightness problem.

these take the same signal strength as a normal scart tv through the analogue input.

as for connecting a c64 to one i wouldnt bother,theres no luma for s/video at the monitor,trust me.
what i would do is this: convert the chroma/luma/composite to analogue c/sync and rgb signals and feed it in that way..that is possible as alot of commodore monitors do exactly that.

[Bryce]

I think I worked out at one time that 150R on the R,G and B lines was what's needed. I know that that's what I use when I make an ST SCART cable. @Gryzor if you open up the ST+ I sent you, you'll probably find I added them inside between the mainboard and the S-Video PCB.

Bryce.

[Token]

as for connecting a c64 to one i wouldnt bother,theres no luma for s/video at the monitor,trust me.
what i would do is this: convert the chroma/luma/composite to analogue c/sync and rgb signals and feed it in that way..that is possible as alot of commodore monitors do exactly that.

The GT-64 is a monochrome green monitor, it use luma. (center pin of DIN 6) The C64 video output is composite. (or correct me)
Bryce though it should work in an older topic, but my tests failed.


I an other hand I could connect the C64 (SECAM version) to a color monitor CTM644-2 and a MP-3f SECAM modulator and a 9V battery (AV).
It also worked with a PAL C64 but of course black and white picture. But also half of the time the C64 BASIC boot screen is in color! But running anything like games makes the screen B&W again.

[roy bates]

The GT-64 is a monochrome green monitor, it use luma. (center pin of DIN 6) The C64 video output is composite. (or correct me)
Bryce though it should work in an older topic, but my tests failed.


I an other hand I could connect the C64 (SECAM version) to a color monitor CTM644-2 and a MP-3f SECAM modulator and a 9V battery (AV).
It also worked with a PAL C64 but of course black and white picture. But also half of the time the C64 BASIC boot screen is in color! But running anything like games makes the screen B&W again.

yes an early c64 is only composite and luma on seperarate pins,all the others had composite chroma and luma.

yes i was thinking ctm640 ctm644 cm14...i dont use monochrome monitors...sorry,i went by the thread title.

early c64's had a trim pot to adjust chroma in the video circuit next to the vic II,you could try to adjust that...one board that comes to mind is the assembly 250407.