Re: Problem Using a Commodore 1084s Monitor on a IIgs

["Polymorph" <polymorph@a2central.com.remove-3n-this>]

 To: Polymorph
Good and bad news...

OK, I have wired up the 200 Ohm pot and it does successfully fix the 
sync problem. The monitor produces a nice crisp image.  :-)  I thought 
it was a matter of case closed. My daughter played with the computer for 
quite a while before I noticed different troubles.

Unfortunately, after the monitor is turned on for about 30-40 minutes, 
it starts making a noise and the screen shimmies a bit (horizontally). 
It seems to be related to the brightness/contrast somehow. Lowering the 
brightness and/or contrast makes the problem appear worse, setting high 
contrast/brightness make the problem go away.

All testing from this point was done with the monitor standalone - i.e. 
there was no input source. I simply left the monitor on until the noise 
recurred and attempted the following.

I opened the case again and tried the horizontal hold adjustment, and it 
changed the pitch of the noise being produced, but that is all.

Originally I thought it was probably the main 150uF 400V capacitor 
making the noise (by ear it sounded in the vicinity), so I replaced it 
with a known good one that I had. It made no difference.

By moving a microphone *carefully* near the components, I was able to 
determine where the noise was coming from (without the use of the 
microphone it was impossible to tell where the sound was coming from). I 
narrowed it down to two components - L301 or L202. I copied the 
schematic for the 1084S-D onto my website:

http://apple2.sytes.net/1084S-D.gif

I took a couple of photo's of the suspected noise makers:

http://apple2.sytes.net/1084a.jpg
http://apple2.sytes.net/1084b.jpg

Now, for my questions:

1) is it likely that one of the components making the noise is faulty, 
or one of the surrounding components? (e.g. a capacitor)
2) if L301 or L202 faulty, are those parts easy to find replacements for?
3) is there something else that is likely causing the noise? Bear in 
mind that I'm fairly confident that the location I have indicated is 
where the noise is coming from (the record levels peaked out around here).

I swear by the end of all this I'll be able to open my own monitor 
repair shop.  :-)

Oh yeah, and why can't I get a monitor that just works?!?

Thanks,
Mike
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