Re: Sick AppleColor composite monitor

[Rubywand <rubywand@swbell.net>]

Seedbat@webtv.net writes ...
> 
> Rubywand and Ed,
> 
> Thanks for responding.
> 
> The only capacitor that even looks suspicious is the wide, short
> cylindrical one right next to what I assume is the power supply. It's
> the only one with the plastic top, which is black. U9188 is printed on
> top. (Since it hugs the metal plate, I can't see what's printed on the
> side without first desoldering it.)
> 
> I don't know if it's normal with these types of capacitors, but its top
> is bulging. There is no discharge however.
> 
> Do you think it could be blown?

     A cylindrical cap encased in plastic may normally have a rounded top.
Plastic (or epoxy) is molded into all kinds of shapes. (If a typical
aluminum-cased electrolytic cap has a rounded top, it is suspect because these
caps almost always have flat tops.)

     The capacitor you are talking about _may_ have heated and swelled. You can
examine the cap and try to decide whether it looks discolored, deformed, etc..
If you remove it, mark its position with white-out (on the cap and board). Once
removed, discharge the cap by shorting its leads. Then, you can note its
capacitance, voltage rating and type. And you can look for any evidence of
cracks or leaking and check the capacitor for an 'open' or short.


     Checking the net led to "Notes on the Troubleshooting and Repair of
Computer and Video Monitors" at http://www.pacwest.net/byron13/sam/monfaq.htm 
by Samuel M. Goldwasser. This doc mentions symptoms similar to yours on other
computer monitors and indicates that the problem may be a blown "S-correction"
capacitor or, maybe, some capacitor(s) in the Vertical output.

     Evidently, the S-correction capacitor is typically located in the vicinity
of the deflection yoke connector or Horizontal Output Transformer. Value seems
to fall roughly in the .05uF --- .5uF range with a voltage rating of 400V or
higher (not sure about these specs, though).

     A posting about a similar problem (on a different monitor) mentioned blown
capacitors in the vertical output-- .1uF and .47uF mylar caps rated at 40V in
series with 2.2 Ohm resistors.

     You may be able to get some good suggestions by posting your question to
the sci.electronics.repair newsgroup.



Rubywand