15khz monitor luminance question

[Minwah]

I've setup my old Amstrad (CTM644) monitor with my Dreamcast using a VGA adaptor.  The picture looks really good but at times seems too dull.  With my Amstrad CPC6128 the picture looks as good and bright as ever.

I know that when wiring up the monitor I ignored the 'luminance' pin as the old Genesis>Amstrad monitor cable I took apart to make my current cable seemed to ignore it.  The name seems to suggest this would make a difference in brightness.  If so, would I be right in thinking I should just connect this pin to ground?

[dabone]

Thats like the old commodore monitors.
It's basically and old style svideo connector. i.e. 2 different composite connectors form the one svideo input.

 Y/C Video, also known as S-Video:
     separate composite luminance (Y) and chrominance (C) signals.




SVIDEO PINOUT

1 GND Ground (Y)
2 GND Ground (C)
3 Y Intensity (Luminance)
4 C Color (Chrominance)

So a svideo connection would go from 3 to the luminance connector (along with it's ground for the shield)
and pin 4 to the composite connector on the monitor (also along with it's ground)



On my commodore 1084 monitor there is a switch to switch between CVBS/LCA (Lca is what they called the original svideo)

hope this helps more than it confuses.

Later,
dabone

[Silver]

But is it using Svideo? I presumed from the VGA adapter comment that its some form of RGB from the dreamcast....

[dabone]

Ok, ignore what I said, it has nothing to do with amstrads.

(Never saw one, I'm from the USA.. just remembered what the commodore monitors of that era were like.)


Does that monitor have a digital and analog rgb mode?

If so maybe it's another label for rgbi?


Later,
dabone

[Minwah]

Thanks for the replies...I should have been clearer.  The monitor has the following pins:

Red
Green
Blue
Gnd
Sync
Luminance

...so I connected all except 'luminance' up as you normally would to an arcade monitor.  As I say it basically works fine, but the picture just looks too dull.  The brightness is on full, but it looks absolutely perfect with the Amstrad computer itself.  I am guessing that the Amstrad monitor lead has this 'luminance' pin wired up somehow.  I've never seen a luminance pin on an RGB monitor before so I am just not sure what to do with it - I think I will try just grounding it and see what happens, unless anyone knows better ??

Cheers

Edit: probably not too important but I found this page with the monitor pinout (scroll down to 'Monitor Connector' 'CPC'):

http://andercheran.aiind.upv.es/~amstrad/docs/connect.html


Edit 2: thinking about it, it would probably make more sense that a voltage should be applied to the luminance pin...maybe I should try connecting R, G or B to it?

As you can tell I am guessing really so any help would be great!

[dabone]

Luminance, Composite Sync and Gnd are the only signals required for a black/white or green-screen display. (e.g. Amstrad GT64 and GT65 monitors).

This line makes me think it just a black and white signal derived from the rgb signals for the older monochrome monitors.


What are the voltage levels of the amstrad? 5v point to point?

Maybe you just need a video amp.



Later,
dabone

[Minwah]

This line makes me think it just a black and white signal derived from the rgb signals for the older monochrome monitors.

Yeah I think you're right...I should have read this

'Red, Green, Blue, Composite Sync and Gnd are the only signals required for a colour display. (e.g. Amstrad CTM640 and CTM644 monitors)'

What are the voltage levels of the amstrad? 5v point to point?

Maybe you just need a video amp.

I am not sure the levels...will try to find out.

I did try a video amp before but couldn't get a stable picture.  I will try again, maybe I wired it up wrong.

Thanks for the help.

[AndyWarne]

Those monitors were probably digital not analog. This means that the red, blue, green guns are either full on , or off. The luminance pin gives another degree of brightness. I am not sure if it needs to be grounded or connected to 5 volts for max brightness, worth trying both.
Andy

[dabone]

Interestingly enough, the graphics chip in early (non-plus) models was the MC6584, the same one used on IBM-PC and compatibles CGA graphics adapters, although the CPC monitor was fully analog and better-suited for multiple resolutions and greater color depths than the typical digital CGA monitor.

Stolen from Wikipedia.

Nope it's analog rgb.

Give the video amp another try, but don't hook up the sync thru it.

(just the rgb)

Later,
dabone

[Silver]

Its possible Luminence is simply a composite input - I've seen old monitors where the luminence input is simply a composite input. Is there any kind of selector on the monitor? I could be wrong though. You could try hooking up some composite video to it and seeing what you get... I can't see any harm in grounding/+5V the luminence pin either.

My bet that its TTL level RGB - ie analog, but expect 5V peak to peak - and your 1V output from a VGA card is just too low. The earlier suggestion of a video amp for the RGB sounds good.

[Minwah]

Give the video amp another try, but don't hook up the sync thru it.

(just the rgb)

Just curious as to what the amp would do to the sync if it is hooked up?  I did hook it up before and the picture seemed very bright and was rolling - not sure if this is due to hooking the sync to the amp or my incorrect wiring.

Thanks again, I have plenty of things to try!

[Silver]

I've not used a video amp - does it even have an input for syncs? - but basically if your syncs are "working" - you have stable pic - theres no need to mess with them. I can only imagine that it was amping your sync signals....

But your sync signals may well alreay be 5V - I think thats what VGA outputs on syncs. No idea if the video amp is trying to up these even more, or just failing to pass them correctly. But if pre-amp its stable and post-amp its not, its definately doing something you don't need. If it was bright and unstable, then sounds like only amping RGB and leaving the syncs will be perfect.

[dabone]

The ultimarc video amp generates a amped composite sync.
PC's have seperate h/v syncs.

Since your dreamcast has the correct sync already don't mess with it.


Later,
dabone

[Harry Potter]

Give the video amp another try, but don't hook up the sync thru it.

(just the rgb)

Just curious as to what the amp would do to the sync if it is hooked up?  I did hook it up before and the picture seemed very bright and was rolling - not sure if this is due to hooking the sync to the amp or my incorrect wiring.

Thanks again, I have plenty of things to try!

I've done a similar hookup before with a 1084S.

All I had to connect was RGB and HV sync to composite. Luminance was not connected.

Also the 1084S style monitor run on NEGATIVE sync. That could cause the image to roll.

[Minwah]

I found this thread:

http://forum.arcadecontrols.com/index.php?topic=31796.0

...basically I'd completely forgot about it (it was just before I went to Oz, that's my excuse  ).


Mostly the same people answered in that thread too...I decided to have the monitor apart and check the 'sub bright' pot as suggested (by Silver).  Adjusted it and it now seems great, and also adjusted the vertical-size to fill the screen too 

Thanks again guys, and sorry for this thread which is a bit dedundant