Short raster on Toshiba TV

[Roger Blake]

My Toshiba 19" color TV set (Model CE910) has developed a problem where the
raster is about an inch or so short at the bottom of the screen, leaving
a black strip which cannot be adjusted out. This can be seen here:

http://s291.photobucket.com/albums/ll302/rogblake/tvproblem/?action=view&current=tvproblem.jpg

The problem occurs no matter what the video source and has actually
gotten a little worse since the above picture was taken. It has
been going on for quite a few years, there is a height control
inside the set and every once in a while I'd just go inside and
adjust it to get the full picture back. Now it's at the point where
the height control is maxed out and the black stripe at the bottom
is creeping up.

On a conventional TV I'd probably check the vertical output tube
for starters, but this is a transistorized set and I'm not quite
sure how to approach it. It actually has been quite reliable over
the years despite the "Made in Japan" label -- aside from occasional
tuner cleanings this is the first repair that has been needed.
(Maybe electrolytic condensers are going bad? The set is about 28
years old.)

Any tips on a possible fix appreciated! (Quips about "buying a new set"
can be sent to /dev/null...)

 

[Chuck]

My Toshiba 19" color TV set (Model CE910) has developed a problem where the
raster is about an inch or so short at the bottom of the screen, leaving
a black strip which cannot be adjusted out. This can be seen here:

http://s291.photobucket.com/albums/ll302/rogblake/tvproblem/?action=view&current=tvproblem.jpg

The problem occurs no matter what the video source and has actually
gotten a little worse since the above picture was taken. It has
been going on for quite a few years, there is a height control
inside the set and every once in a while I'd just go inside and
adjust it to get the full picture back. Now it's at the point where
the height control is maxed out and the black stripe at the bottom
is creeping up.

On a conventional TV I'd probably check the vertical output tube
for starters, but this is a transistorized set and I'm not quite
sure how to approach it. It actually has been quite reliable over
the years despite the "Made in Japan" label -- aside from occasional
tuner cleanings this is the first repair that has been needed.
(Maybe electrolytic condensers are going bad? The set is about 28
years old.)

Any tips on a possible fix appreciated! (Quips about "buying a new set"
can be sent to /dev/null...)

It is probably is an electrolytic. From memory, the most common ones
were c302, C307 and C310. If you have an ESR meter, check
eletrolytics in the vertical area and in the metal case which contains
the jungle chip. Chuck

 

[Roger Blake]

It is probably is an electrolytic. From memory, the most common ones
were c302, C307 and C310. If you have an ESR meter, check
eletrolytics in the vertical area and in the metal case which contains
the jungle chip. Chuck

Thanks, I'll take a look for those. Is there any place online that
has a schematic and/or component layout diagram?

 

[tm]

My Toshiba 19" color TV set (Model CE910) has developed a problem where
the
raster is about an inch or so short at the bottom of the screen, leaving
a black strip which cannot be adjusted out. This can be seen here:


http://s291.photobucket.com/albums/ll302/rogblake/tvproblem/?action=view&current=tvproblem.jpg

The problem occurs no matter what the video source and has actually
gotten a little worse since the above picture was taken. It has
been going on for quite a few years, there is a height control
inside the set and every once in a while I'd just go inside and
adjust it to get the full picture back. Now it's at the point where
the height control is maxed out and the black stripe at the bottom
is creeping up.

On a conventional TV I'd probably check the vertical output tube
for starters, but this is a transistorized set and I'm not quite
sure how to approach it. It actually has been quite reliable over
the years despite the "Made in Japan" label -- aside from occasional
tuner cleanings this is the first repair that has been needed.
(Maybe electrolytic condensers are going bad? The set is about 28
years old.)

Any tips on a possible fix appreciated! (Quips about "buying a new set"
can be sent to /dev/null...)

--

Look for a non-polar electrolytic around 10 uF or so, 50 to 100 volts.
In the vertical drive to the yoke.

As old as that set is, suspect any of the electrolytic. Borrow an ESR meter
from someone.

 

[William Sommerwerck]

There is something to be said for shotgunning the caps, especially the
electrolytics.

 

[Roger Blake]

There is something to be said for shotgunning the caps, especially the
electrolytics.

I was thinking along those lines, particularly given the gradual nature
of the problem (electrolytics slowly deteriorating).

You guys have definitely given me some ideas to go on, thanks! I'm going
to open up the set and inventory the caps, particularly those in the
vertical section if I can identify that area. The set has a single circuit
board in the bottom where the majority of the components are located.

 

[shrtrnd]

possible vertical output transistor on the way out

 

[Roger Blake]

And unless you are skilled at carrying out such work, that 'something' is
"don't" ...

I am admittedly more at home working with tube electronics, and mostly
audio and radio for that matter, but am no stranger to replacing caps
and other components on a printed circuit board. As long as I don't
do anything stoopid to electrocute myself the worst that can happen
to screw it up and having to replace the set...

Fortunately the vertical section is clearly marked on the main PC
board. I've inventoried the caps in that area and will start there,
though I was unable to find all the ones that Chuck mentioned ...
The c302 is physically located in the adjacent horizontal section.
I have not found c307 or c310, though the c3xx numbered caps do
seem to be primarily located in the vertical area and those are the
ones I'm targeting for replacement.

Also I need to retract my earlier "Made in Japan" quip - even though Toshiba
is a Jap company, it turns out this set is actually made in the U.S. and
contains a lot of US-made components, including the picture tube!

 

[Cydrome Leader]

There is something to be said for shotgunning the caps, especially the
electrolytics.

agreed.

I still fix the CRT based computer monitors I have. Any goofy geometry or
strange scan lines are bad caps.

 

[[email protected]]

My Toshiba 19" color TV set (Model CE910) has developed a problem where the
raster is about an inch or so short at the bottom of the screen, leaving
a black strip which cannot be adjusted out. This can be seen here:

http://s291.photobucket.com/albums/ll302/rogblake/tvproblem/?action=view&current=tvproblem.jpg

The problem occurs no matter what the video source and has actually
gotten a little worse since the above picture was taken. It has
been going on for quite a few years, there is a height control
inside the set and every once in a while I'd just go inside and
adjust it to get the full picture back. Now it's at the point where
the height control is maxed out and the black stripe at the bottom
is creeping up.

On a conventional TV I'd probably check the vertical output tube
for starters, but this is a transistorized set and I'm not quite
sure how to approach it. It actually has been quite reliable over
the years despite the "Made in Japan" label -- aside from occasional
tuner cleanings this is the first repair that has been needed.
(Maybe electrolytic condensers are going bad? The set is about 28
years old.)

Any tips on a possible fix appreciated! (Quips about "buying a new set"
can be sent to /dev/null...)

One other weak point in the vertical deflection circuit is the solder
joints. Resolder any connections on the vertical output driver and
it's heat sink.

PlainBill