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...)

--
Roger Blake
Change "invalid" to "com" for email.
Google Groups killfiled due to spam.

 

[Chuck]

On Wed, 23 May 2012 18:37:38 +0000 (UTC), Roger Blake
<rogblake@iname.invalid> wrote:

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

 

[Ian Field]

"Roger Blake" <rogblake@iname.invalid> wrote in message
news:20120523182050@news.eternal-september.org...

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

One possibility is the flyback tuning capacitor, in the vicinity of the
H-sweep transistor and/or the E/W modulator diodes (one of those could be
leaky).

The capacitor could be a resin dipped foil type - in which case it might be
visibly bulged, sometimes its a resin dipped disc ceramic - they normall
crack and show a small burn mark on the resin, but the symptoms are usually
same as a SC sweep transistor.

If you have to delve deeper into fault finding, it looks as if the
deficiency is on the LHS - the line pulse drives the beam from the middle to
(your) RHS, at the end of that pulse is the flyback pulse which takes the
beam rapidly to the LHS & generates the EHT - its the recovery of this
energy stored in the resonant circuit that drives the beam from LHS back to
where the next line pulse takes over

 

[Roger Blake]

On 2012-05-23, Chuck <ch@dejanews.net> wrote:

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?

--
Roger Blake
Change "invalid" to "com" for email.
Google Groups killfiled due to spam.

 

[tm]

"Roger Blake" <rogblake@iname.invalid> wrote in message
news:20120523182050@news.eternal-september.org...

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.

 

[Ian Field]

"tm" <No_one_home@white-house.gov> wrote in message
news:jpjl60$aso$1@dont-email.me...

"Roger Blake" <rogblake@iname.invalid> wrote in message
news:20120523182050@news.eternal-september.org...
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.

The shadow on the LHS threw me.

IIRC NP electrolytic coupling caps in the vertical OP are comparatively rare
except in portables - but if that model has one its a good place to start.

Another place worth looking is the CR timing network in the VTB charging
circuit and/or the linearity network (sometimes includes a preset pot).

 

[William Sommerwerck]

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

 

[hr(bob) hofmann@att.net]

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.- Hide quoted text -

- Show quoted text -

I would suggest looking for a large lectrolytic, either polarized or
non-polarized, in the connection from the verical output transistor to
the deflection yoke. Odds are at least 10 - 1 that is the problem.
And, please let us know what you do find, it adds to the total
knowledge on this site.

 

[Roger Blake]

On 2012-05-23, William Sommerwerck <grizzledgeezer@comcast.net> wrote:

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.

--
Roger Blake
Change "invalid" to "com" for email.
Google Groups killfiled due to spam.

 

[Arfa Daily]

"William Sommerwerck" <grizzledgeezer@comcast.net> wrote in message
news:jpjmjl$j8r$2@dont-email.me...

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

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

Arfa

 

[Roger Blake]

On 2012-05-25, Arfa Daily <arfa.daily@ntlworld.com> wrote:

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!

--
Roger Blake
Change "invalid" to "com" for email.
Google Groups killfiled due to spam.

 

[Cydrome Leader]

William Sommerwerck <grizzledgeezer@comcast.net> wrote:

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.

 

On Wed, 23 May 2012 18:37:38 +0000 (UTC), Roger Blake
<rogblake@iname.invalid> wrote:

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