Philips 4CM4270/00T red problems

[Andreas Schmidt]

Hi all,

The 4CM4270/00T is an old fully analog 14 inch multisync monitor.

The problem was originally that the red color was completely missing on
turn-on and would set in after about 10 minutes of warm-up. I reseated
the neck board and reflowed all leaded components. Now the picture was
good on turn-on, but after about 20 minutes of running, the red color
would completely go. Next I desoldered the red coupling cap and checked
its ESR, which turned out to be fine. Soldered the cap back in, removed
the neck board, cleaned the CRT contacts and put the board back on. Now
the picture has almost all of the red (but still a bluish tint) on
turn-on, but after about ten minutes of running, a) the color becomes
normal (more red) and b) the picture becomes brighter (could be due to
the red color coming back, not sure if the brightness change happened
before, but a) and b) occur at exactly the same time). BTW, all those
changes happen instantaneously, not gradually.

I'm starting to suspect the CRT itself. Anything else I could try? Could
the LM1203 or a transistor fail in a way that would produce these symptoms?

Thanks for your help,

Andi

--
If Mr. Edison had thought smarter he wouldn't sweat as much.
- Nikola Tesla

 

[Jerry G.]

If you can get a scope the best bet is to trace the signal back along
its path to see where the failure is. This is something you can guess at
forever, and there is too many parts involved. If the red bias and
signal is good to the CRT and the picture is bad, then you know it is
the tube. By your description, I would first assume it is a defective
component along the video path in the red channel.

--

Greetings,

Jerry Greenberg GLG Technologies GLG
==============================================
WebPage http://www.zoom-one.com
Electronics http://www.zoom-one.com/electron.htm
Instruments http://www.zoom-one.com/glgtech.htm
==============================================
"Andreas Schmidt" <me@privacy.com> wrote in message
news:bj9i5b$gnnhn$1@ID-205044.news.uni-berlin.de...
Hi all,

The 4CM4270/00T is an old fully analog 14 inch multisync monitor.

The problem was originally that the red color was completely missing on
turn-on and would set in after about 10 minutes of warm-up. I reseated
the neck board and reflowed all leaded components. Now the picture was
good on turn-on, but after about 20 minutes of running, the red color
would completely go. Next I desoldered the red coupling cap and checked
its ESR, which turned out to be fine. Soldered the cap back in, removed
the neck board, cleaned the CRT contacts and put the board back on. Now
the picture has almost all of the red (but still a bluish tint) on
turn-on, but after about ten minutes of running, a) the color becomes
normal (more red) and b) the picture becomes brighter (could be due to
the red color coming back, not sure if the brightness change happened
before, but a) and b) occur at exactly the same time). BTW, all those
changes happen instantaneously, not gradually.

I'm starting to suspect the CRT itself. Anything else I could try? Could
the LM1203 or a transistor fail in a way that would produce these
symptoms?

Thanks for your help,

Andi

--
If Mr. Edison had thought smarter he wouldn't sweat as much.
- Nikola Tesla