[GreenKeys] CRT Left side char distortion...

Wed Sep 16 13:49:19 EDT 2015

Time to get out a pad of graph paper, a good eraser and a few sharp
pencils. One should be able to draw out the schematic of the monitor in a
couple hours. But before that fire up the unit .. oh btw, WATCH OUT SOME
PRETTY MEAN VOLTS .. look for caps in the sweep area. If you can't
find a value for a part don't worry.

Once you have a drawing, check the value of resistors, caps are a bit
harder if you don't have the ability to measure them, electrolytics if not
open are a bit harder. Don't find anything, start probing around with a
'scope.

Fingers crossed it is not a shorted yoke, but in the little monitors that
was pretty uncommon.

Worse case .. what size monitor is it ?

-pete

On Tue, Sep 15, 2015 at 12:33 PM, Chris Elmquist <chrise at pobox.com> wrote:

> On Tuesday (09/15/2015 at 03:19PM -0400), Keith Densmore wrote:
> > Good thoughts, and I thank you. The problem is made worse by the fact
> that Hal
> > rarely provided schematics for his stuff. The monitor section appears to
> be a
> > Japanese sub assembly but I have no schematic for it.
> > I
> > don't suppose anyone would by some miracle have a schematic for the Hal
> Telereader 6850? Or just a schematic of any greenscreen monitor, I'm
> > sure they are all similar.
> > I'd try replacing/checking caps if I had something to go by.
>
> I can't offer help with a manual but I did track down the vintage
> (1981 perhaps),
>
> http://www.eham.net/reviews/detail/5857
>
> but indeed it was built in Japan by "Comax" so you need to track down
> a Japanese monitor schematic I suppose.  Not sure what would be similar
> from that era?
>
> Neat unit though.  Curious what microprocessor is in it when you get
> the cover off...
>
> Chris NØJCF
>
> > Original Message:
> > From: Chris Elmquist <chrise at pobox.com>
> > To: Kenneth Gartland <trnsrme at gmail.com>
> > Cc: <GreenKeys at mailman.qth.net>
> > Sent: 2015-09-15 3:05:54 PM
> > Subject: [GreenKeys] CRT Left side char distortion...
> >
> >
> > I had similar thoughts as Ken but also the possibility that the CRT
> > may need a degaussing. Not sure when degaussing coils became integral
> > and automatic but it's
> > possible that while this tube "held down the
> > closet", it got magnetized
> > externally in a non-uniform way and this is
> > now distorting the image.
> >
> > I have seen this when a video monitor was stored next to the large steel
> > chassis of another piece of equipment and this warped the image after
> > that CRT was pulled out and powered up.
> >
> > If the gear has an integral degaussing coil and does it automatically
> > at power up (the image will wiggle right after power up if so) then you
> > can probably discount this idea.
> >
> > https://en.wikipedia.org/wiki/Degaussing
> >
> > Chris NØJCF
> >
> > On Tuesday (09/15/2015 at 02:51PM -0400), Kenneth Gartland wrote:
> > > Hi all...
> > >
> > >
> > Keith's problem of char distortion, is likely linear sweep as mentioned
> > > already, but maybe as simple as a 'Deflecting
> > magnet" having dropped
> > > (Unglued) from the CRT area just ahead of the yoke ass'y...
> > >
> > > Many of the older, especailly cheaper, CRT's used as computer monitors,
> > > used these stick on magnets to cure all kinds of deflection issues,
> especially
> > > in the corner areas of the tube...
> > >
> > > Some magnets were held on by a silicone seal adhesive, or equiv., and
> some
> > > were fastened with an adhesive pad...
> > >
> > > Best for Keith to check in the base of the CRT area to see if this is
> > > the case...
> > > They usually fall off and go straight down, where you can't. get at
> > > them of course!!
> > >
> > > Almost forgot!...If the CRT has 'Centering' tabs on the CRT neck,
> moving the
> > > tab up or down on the left side mite clr the problem...Use an orange
> stick or
> > > some other insulated tool to carefully move the tab...Lotsa HV in
> > > there so one has
> > > to be carefull!
> > >
> > > Hope this helps a bit...
> > >
> > > Cheers!
> > >
> > > Ken VE3-HMQ
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> > --
> > Chris Elmquist
> >
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> --
> Chris Elmquist
>
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