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From: kim@amdahl.UUCP (Kim DeVaughn)
Newsgroups: comp.sys.amiga
Subject: Re: Popping monitor
Message-ID: <4344@amdahl.UUCP>
Date: Tue, 25-Nov-86 16:46:09 EST
Article-I.D.: amdahl.4344
Posted: Tue Nov 25 16:46:09 1986
Date-Received: Wed, 26-Nov-86 03:43:06 EST
References: <685@husc6.UUCP>
Distribution: net
Organization: Amdahl Corporation,  Sunnyvale, CA 94086
Lines: 68

In article <685@husc6.UUCP>, may@husc4.harvard.edu (jason may) writes:
> 
> 	Since I got my Amiga over the summer, I have had a problem with
> my monitor frequently making popping or snapping noises, very quietly,
> accompanied by a flash from the screen.  This is not a normal Amiga
> error-screen-flash flash, but a very fast jump of the whole image.

Yeah, my monitor started doing the same thing about a month or so after
I got it.  This was one of the early units, from over a year ago, and at
that time, someone on the net from CBM said that there had been a problem
with "overspray" of the material that's used to conduct the the high-
voltage from the connector in the side of the CRT to the front of the tube.
The suggested fix was to return it to the dealer who could remove the over-
spray.

Since it was still in the Warranty period, I took the monitor in, and of
course it didn't arc at all for the dealer :-).  Back home, it arced every
90-120 seconds.  Back to the dealer with the whole system ... no arcing.

OK, we're dealing with a high-voltage leak, which are very sensitive to
humidity, temperature, etc., so the only thing to do is shoot the bug
"in place".

I took the cover off, and inspected all around the CRT, high-voltage
connector (where the fat red wire attaches to the side of the tube), CRT
socket, and high-voltage power supply (where the fat red wire comes from)
for any sign of "overspray" or "carbon tracking" (fine lines of black soot)
on/around these areas.  Nothing.

Finally, with the cover still off, I powered the monitor up in a DARK room,
and waited until it started arcing.  After a few pops, I spotted the tiny
flash from the spark coming from underneath the high-voltage power supply,
somewhere near the left-most edge of the circuit board.

I powered down the monitor, and removed the H-V supply (after first making
SURE that the CRT was unplugged, *and* that the H-V connection at the CRT
had been discharged to ground using a wire attached to ground on one end,
and clipped to a screwdriver on the other;  you touch the tip of the screw-
driver to the H-V connection under the little plastic insulator cup where
the fat red wire attaches to the tube).

Anyway, inspection of the bottom of the H-V circuit board showed no sign
of an H-V leak (carbon tracks, etc), but some of the solder spots where
the various components are connected were "sharp".  Carefully, with a pair
of finger-nail clippers, I clipped all the little tips as close to the
PC board as possible, and then smoothed them down using a small nail file.

Reassembled the H-V supply and cover, and ... no arcing!  And none since.


Hope this little narrative helps!

/kim


P.S.  If you try this make VERY SURE that the H-V terminal at the CRT gets
      fully discharged!  That circuit can hold onea helleva big charge
      (20-30 kV) for a LONG time (hours).


-- 
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[  Any thoughts or opinions which may or may not have been expressed  ]
[  herein are my own.  They are not necessarily those of my employer. ]