Re: Problem with AppleColor composite monitor

[mjmahon@aol.com (Michael J. Mahon)]

RPM (sirarlias@webtv.net) wrote:

>I'll clarify a few things (I'm learning):
>
>By "tabs" I meant the trimpots along the right side. I didn't touch the
>magnet adjustments on the back of the CRT.

Good!  The magnets can be hard to readjust without a test
pattern generator.

>I hooked the monitor to two other computers and it still exhibited the
>same problem.

So we know it's the monitor--unless you used the same cable
for all tests.  Check the cable, too.  And the connector on the
monitor.  Something as simple as a bad connection or a bent or
broken pin could produce the symptom you describe.

>I ran a program that uses a white backround and pushed the color kill
>switch: the screen has a bluish-green tint.

Yep--no red signal.

>Thanks for your help.

You're welcome--hope you get it working.  If it _is_ the internals
of the monitor, then you should first verify that the red gun is
working--by getting _some_ red on the screen, even if weak.

If this works, then you are looking for a break (or big loss of
gain) in the red video signal.  The easiest way to find this (after
a simple inspection and maybe some continuity tests) would
be to use an oscilloscope to compare waveforms on the red
channel versus corresponding points on either the blue or the
green channel, while displaying something that's black and white.

When you find the earliest (closest to the input) gross difference,
you've located the problem in the immediately preceding (in signal
flow) component(s).  Needless to say, this is easier with a circuit
diagram.  ;-(

Good luck!


-michael

 Email:  mjmahon@aol.com
 Home page:  http://members.aol.com/MJMahon/