Sony KV-32S40 Horiz. Drive Problem

[Chris F.]

This set is proving to be a tough fix. I picked it up in the trash a while
ago, and when I first tried it everything seemed to work fine. After about
half an hour though the picture went very dark and shrunk in on the sides.
The problem is permanent now and will not go away. All voltages on the
secondary of the flyback - HV, CRT filament, etc. are about 30% below normal
but the B+ is a solid 136V. All voltages from the power supply are good, and
there are no bad caps... it seems like the horiz. drive signal isn't strong
enough. I tried replacing the horizontal driver transistor as well as all
electrolytics in that area, and fixed some cold solder as well, but it made
no difference.
Any ideas?

 

[Mark Zacharias]

This set is proving to be a tough fix. I picked it up in the trash a
while ago, and when I first tried it everything seemed to work fine. After
about half an hour though the picture went very dark and shrunk in on the
sides. The problem is permanent now and will not go away. All voltages on
the secondary of the flyback - HV, CRT filament, etc. are about 30% below
normal but the B+ is a solid 136V. All voltages from the power supply are
good, and there are no bad caps... it seems like the horiz. drive signal
isn't strong enough. I tried replacing the horizontal driver transistor as
well as all electrolytics in that area, and fixed some cold solder as
well, but it made no difference.
Any ideas?

Did you resolder the horizontal drive transformer?

Mark Z.

 

[N_Cook]

This set is proving to be a tough fix. I picked it up in the trash a while
ago, and when I first tried it everything seemed to work fine. After about
half an hour though the picture went very dark and shrunk in on the sides.
The problem is permanent now and will not go away. All voltages on the
secondary of the flyback - HV, CRT filament, etc. are about 30% below normal
but the B+ is a solid 136V. All voltages from the power supply are good, and
there are no bad caps... it seems like the horiz. drive signal isn't strong
enough. I tried replacing the horizontal driver transistor as well as all
electrolytics in that area, and fixed some cold solder as well, but it made
no difference.
Any ideas?

Sometimes a failing/ed non-polarised capacitor in the flyback area causes
that problem

 

[Mark Zacharias]

Did you resolder the horizontal drive transformer?

Mark Z.

After you run the set for a few minutes, turn it off and see how hot
the horizontal/flyback transformer is. If it is scorching hot, there
may be a shorted turn on the transformer, that will cause what you are
seeing..

I think if that were the case, the horizontal output transistor would have
died in short order. Of course, the bad solder at the drive transformer,
which is VERY common, can and does kill the output transistor also; I was
just thinking the OP had been lucky up to this point.

Mark Z.

 

[Meat Plow]

This set is proving to be a tough fix. I picked it up in the trash a
while ago, and when I first tried it everything seemed to work fine.
After about half an hour though the picture went very dark and shrunk in
on the sides. The problem is permanent now and will not go away. All
voltages on the secondary of the flyback - HV, CRT filament, etc. are
about 30% below normal but the B+ is a solid 136V. All voltages from the
power supply are good, and there are no bad caps... it seems like the
horiz. drive signal isn't strong enough. I tried replacing the
horizontal driver transistor as well as all electrolytics in that area,
and fixed some cold solder as well, but it made no difference.
Any ideas?

NP tuning caps? Cold solder flyback pins?

 

[Stefan Heimers]

Chris F. wrote:

Any ideas?

Resolder all power semiconductors which are mounted on heat sinks or the
metal frame of the chassis.

Stefan