Re: Losing "North" Vertical Deflection Viewsonic PT775

From: James Sweet (jamessweet_at_hotmail.com)
Date: 11/09/04 

Date: Tue, 09 Nov 2004 03:35:08 GMT

"Nomen Nescio" <nobody@dizum.com> wrote in message
news:102860070e2ae28769d8d3a8b89617e2@dizum.com...
> My 6 year old Viewsonic PT775 occasionally loses vertical deflection for
> just the top half of the CRT. What happens is a very bright horizontal
> trace appears exactly midpoint across the screen, the top half is gone,
> and the image below is normal. Is this a yoke problem or something on a
> PCB? I wasn't aware that there might be circuits controlling upper and
> lower vertical deflection, but that's what appears to be happening.
>
> Of course this is an intermittent problem. Right now I'm using the thing
> and it's working fine. An hour ago it did what I described above. Was
> getting ready to take the back off (again) and wiggle some wires around
> the yoke, all in the hope of finding some loose connection. No such luck
> though, as now it's working perfectly normal. I can't seem to induce or
> reproduce the problem. Just happens on its own. If I should be lucky
> enough such that it fails continually as I described, what would be the
> areas to investigate?
>

Stop using it immediately before you damage the CRT. Find the vertical
output chip, it should be on the main circuit board bolted to a little
heatsink, it'll have 6-12 pins on it, resolder those pins and the monitor
should be back to normal. Chances are you'll see visible cracks in the
solder around the pins.

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