Amstrad monitor - dull

[Minwah]

I have an old Amstrad CTM644 colour monitor (14"), which is 15khz and has a nice RGB input - I'm thinking about using it for a vertical bar-top.  However, its a good 15 years old and the picture is really dull, even with brightness all the way up.

I read that bad flyback transformers can cause this, but I know nothing about monitors so I'm not sure.  Anyone know what could be wrong with it?

[menace]

have you tried adjusting the screen control on the flyback directly?  a little goes a long way here so it sort of has to be on--be very careful though, it would be a pity to lose the creator of mamewah    especially when you have yet to create pinwah (wink, wink, nudge, nudge)

[Ken Layton]

Actually, a bad flyback would cause focus, blooming, or short circuit problems. If your monitor is 15 years old then in my expert opinion, I'd say you have 1 of these two problems: either bad capacitors (very likely) which affect brightness or you have a weak picture tube (that can be repaired most of the time by using a picture tube rejuvenator unit).

[Minwah]

Thanks guys

Are bad caps visibly bad (leaking?) ?

Is a 'picture tube rejuvenator' something I could personally buy / use, or would it need expert attention?

[menace]

not usually--they typically have completely failed when they leak--but after 10-15 years of service its a safe bet they are on their way out.  A rejuvenator is something only a tv repair place is likley to have and even then, doing an arcade monitor might be out of their range of operations--doesn't hurt to ask though. The guys around here looked at me like i have 2 heads whenever i asked.

So the flyback brightness(screen) control made no difference to brighten it?

[Minwah]

not usually--they typically have completely failed when they leak--but after 10-15 years of service its a safe bet they are on their way out.  A rejuvenator is something only a tv repair place is likley to have and even then, doing an arcade monitor might be out of their range of operations--doesn't hurt to ask though. The guys around here looked at me like i have 2 heads whenever i asked.

I know what you mean!

So the flyback brightness(screen) control made no difference to brighten it?

Sorry I haven't had chance to try yet...I'm not 100% sure what I'm looking for so I might be back to ask...

[AndyWarne]

Amstrads were always rather dull anyway... hehe.

I would agree, try the screen control.

Andy

[Silver]

Hey,

I believe the amstrad CTM644 has a variable resistor on the pcb for this...

Open up the back of the monitor. On the PCB there should be a variable resistor call "SUB-BRIGHT" or "BRIGHT-SUB" or something. Can't remember which way to turn it, but make sure the external "brightness" control is at max when you set this. Can't remember which way to turn it.

Of course, if the caps are knackered then this may not help much, but you may be able to squeeze some more juice from it.

The only other thing I can think of is Voltage levels....  I know the amstrad used an 8-pin din socket, but I'm not sure what voltage levels it was expecting (0.7V/1V/5v etc...).

Hmmm a rather cheeky (and no doubt someone will say why its a bad idea) idea is that you could un-terminate the video signal (inducing a fault where the picture is really bright) and then lower the brightness to your liking with the internal pot..... This may not work though, depending on the range of the pot.

[Minwah]

Amstrads were always rather dull anyway... hehe.

Hey!  Nothing wrong with the old CPC's! 

[Minwah]

The only other thing I can think of is Voltage levels....  I know the amstrad used an 8-pin din socket, but I'm not sure what voltage levels it was expecting (0.7V/1V/5v etc...).

I didn't even think of that...but you could well be right.  I tried it with my ArcadeVGA and it was dull......but I should get the old Amstrad CPC6128 and see what that outputs like, maybe it just needs a video amp.

Thanks for all the replies, I have plenty to look into!

[Minwah]

Good news!  I tried the monitor with the Amstrad CPC itself, and it looks fine, so I guess I just need a video amp for the ArcadeVGA output.

Thanks for all the help!

[Silver]

Good stuff - I think Andy sells a video amp if you need (or you could make your own). 

VGa cards output 1V levels I think, amp will up it to 4V or so. Of course easy way would be to stick multimeter onto your amstrad output....

[dabone]

Andy's is a lot cheaper than the roll your own, (Unless you already have the parts)

The avga card output is standard vga levels.. .7 volts point to point.
(Meaning the level varies fro 0v to .7 of a volt.. Not a lot of difference there now is there?)



The standard arcade level is 5 volts point to point.
0-5 volts, over a 500% increase in input levels.



His adapter is only 15 euros, and If I remember right, he's close to you.


Later,
dabone