Re: Red Streak on picture.....

The message <fxKki1DEdPFDFwOL@xxxxxxxxxxxx>
from tony sayer <tony@xxxxxxxxxxxx> contains these words:

> In article <2005083003511085168@xxxxxxxxxxxxxxxx>, Johnny B Good
> <jcs.computers***@xxxxxxxxxxxxxxxx> writes
> >The message <m5UqAeB7O3EDFwhr@xxxxxxxxxxxx>
> >from tony sayer <tony@xxxxxxxxxxxx> contains these words:
> >
> >> In article <3nh951F1gfjcU1@xxxxxxxxxxxxxx>, Ivan
> >> <ivan'H'older@xxxxxxxxx> writes
> >> >
> >> >"Ivan" <ivan'H'older@xxxxxxxxx> wrote in message
> >> >news:3nh5ucF1h449U1@xxxxxxxxxxxxxxxxx
> >> >>
> >> >> "Advid" <advid@xxxxxxx> wrote in message
> >> >> news:devmsa$n7b$1@xxxxxxxxxxxxxxxxxxxxxxxx
> >> >> > ... for the past few weeks my TV (Sony Trinitron - 29 inch -
> >> >> > 4:3) has a
> >> >> red
> >> >> > streak on the right hand side of any part of the picture that
> >> >> > is bright
> >> >> > (white). Is this a sign that the red tube gun is wearing out or
> >> >> > that the
> >> >> > tube itself is on its way out....
> >
> > If that were so, you _wouldn't_ be seeing any red.
> >
> >> >> >
> >> >> > It seems to be getting worse... any bright part of a picture
> >> >> > has a red
> >> >> > shadow 'outline' on the right up to about a quarter of an inch
> >> >sometimes -
> >> >> > but usually about 1/8th inch...
> >> >>
> >
> >> Sounds very much like the Red gun is coming to the end of its useful
> >> life!...
> >

> Years ago we used to look after some 3000 odd rental sets, and we
> replaced numerous CRT's for this very symptom and in every case that was
> the cause.

> If you think its an electo on its way out, then which one, and where is
> it and what does it do, and can you explain how it can cause this
> effect?......

Let's put it this way, To get bright white requires all 3 guns to be
working. The symptom suggests he's getting a little more red than he
should be getting. It's as if the red channel of the three video amps is
being driven to clipping and latching up due to lack of LF response in
the negative feedback circuit.

Of course, this could also arise if the gain of the red channel has
been turned up to compensate for reduced cathode emission in the red gun
(assuming seperate cathodes for each 'colour gun'). However, this sort
of colour balance adjustment either requires access to a PCB mounted
trimpot or, in later designs, access to a service menu.

Since Advid failed to mention making any such adjustments, I'm making a
reasonable assumption that the most probable cause would be dried out
electrolytics in either the red channel or possibly similar defects in
the green and blue channels.

Of course, since even with improved emission red phosphors, the red gun
is worked harder to get the red brightness to match the green and blue,
it might be that compensation by increasing the contrast and brightness
has pushed the red into clipping whilst the other two video channel amps
still have some clipping headroom left.

I know that dried out caps can produce the inverse effect such as the
green channel losing LF response and only allowing green to be present
on the left hand side of what should be a larger patch of green. I was
simply suggesting another possibility other than the 'one size fits all'
snap diagnosis of attributing almost every fault to the picture tube.

--
Regards, John.

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