Sony KV-2784R horiz problem

[[email protected]]

Sony KV-2784R died - horiz collapse - fuse F501 blown - pressing power
button causes TV to try to start then stops - very soft high freq buzz
is heard. Remote control will not start it. HOT and all diodes in area
test OK with ohmmeter. Fuse is somewhat blackened at end where it
seperated, so it wasn't a slight overload. I do not have schematics.
Is there any history of common component failures here.Just for ref, I
am very technical and had a repair shop in the 80's - this was built
11/86 - just after I closed the shop. So speak to me at that level,
thx.

 

[David Farber]

Sony KV-2784R died - horiz collapse - fuse F501 blown - pressing power
button causes TV to try to start then stops - very soft high freq buzz
is heard. Remote control will not start it. HOT and all diodes in area
test OK with ohmmeter. Fuse is somewhat blackened at end where it
seperated, so it wasn't a slight overload. I do not have schematics.
Is there any history of common component failures here.Just for ref, I
am very technical and had a repair shop in the 80's - this was built
11/86 - just after I closed the shop. So speak to me at that level,
thx.

If you post your e-mail address, I can help you with the schematic.

 

[[email protected]]

Thx for the replies..

I pulled the chassis to bring it home - the set is at my other house
and I did not have any tools there.

Therefore I have not replaced the fuse yet as I have nothing to
connect it to.

I was thingking about a low voltage issue because of the remote not
working, I just don't know where that fuse is in the ckt and something
is getting volts as it tries to start. Since it was near the horiz
section I made an assumption. could be wrong.
Don't know if the whistle I hear is the horiz freq or the switching
supply.

tipsnews at nc.rr.com

thanks David.

 

[[email protected]]

I was thinking that is was the AC line fuse that was blackened.
however from what you said it doesn't sound like it. I don't know what
other fuse you could be referring to other than a small chemical fuse
on a 27 inch set though. Lenny.

the AC comes in on the right, passes thru some rectifiers and large
caps etc. There is a small metal box on the left which I believe has a
switching PS in it - haven't opened it yet.
The fuse is about in the middle on the back edge - a mini fuse - just
about where the horiz section starts - the HOT is on the left side
near the box.
I don't see another fuse and none near the ac line.

 

[Chuck]

Sony KV-2784R died - horiz collapse - fuse F501 blown - pressing power
button causes TV to try to start then stops - very soft high freq buzz
is heard. Remote control will not start it. HOT and all diodes in area
test OK with ohmmeter. Fuse is somewhat blackened at end where it
seperated, so it wasn't a slight overload. I do not have schematics.
Is there any history of common component failures here.Just for ref, I
am very technical and had a repair shop in the 80's - this was built
11/86 - just after I closed the shop. So speak to me at that level,
thx.

Most common failure on these is a shorted flyback. Chuck

 

[[email protected]]

Thanks Chuck, I was just going to ask that.

How is it usually checked.

There is no continuity between coils at DC.
coil resistance seems within reason but as low as it is that probably
isn't a very good test.
I haven't got one laying around to sub.
It is, after all, 24 yrs old. But the CRT is still OK.

Can they be had and at what price????????

 

[jerryg50]

Sony KV-2784R died - horiz collapse - fuse F501 blown - pressing power
button causes TV to try to start then stops - very soft high freq buzz
is heard. Remote control will not start it. HOT and all diodes in area
test OK with ohmmeter. Fuse is somewhat blackened at end where it
seperated, so it wasn't a slight overload. I do not have schematics.
Is there any history of common component failures here.Just for ref, I
am very technical and had a repair shop in the 80's - this was built
11/86 - just after I closed the shop. So speak to me at that level,
thx.

I don't know your model in particular. I've worked on many other Sony models. I will tell you generically the common fault.

It's very common the flyback assembly in these sets fail. Along with that, there may be some damage in the main power supply and some of the support components. Start by replacing the flyback assembly. If the HV multiplier is a separate unit in your model of TV, replace that unit at the same time as the flyback assembly.

Jerry G.

 

[Chuck]

Thanks Chuck, I was just going to ask that.

How is it usually checked.

There is no continuity between coils at DC.
coil resistance seems within reason but as low as it is that probably
isn't a very good test.
I haven't got one laying around to sub.
It is, after all, 24 yrs old. But the CRT is still OK.

Can they be had and at what price????????

If you have a scope with a ten times probe, set the V. input for the
highest voltage possible and the H. rate at 20 us and connect the
probe to the HOT collector after plugging the tv into an isolation
transformer. Replace the blown fuse and turn on set. If there is
ringing between the HO pulses, power the set down immediately and
order a flyback replacement. I'd check MCM for a replacement. If
they don't have them, sometimes an Asti flyback will work in a Sony
set. (I haven't had any luck with them for other brands.) Chuck

 

[[email protected]]

OK, I am operating on probabilities here. The rest of the set is 300
miles away. I have a scope and other necessaries but can't plug the tv
in. My extension cords are not long enough. I can get a new fbt for
about $15. what is the probability that will fix it when I carry the
chassis back and fire it up????????????

I have checked all semis with an ohmmeter and find nothing unusual.
The set is 24 yrs old and neer had a problem.
Caps all respond properly to an ohmmeter. I could pull some parts and
ring them with ac but....

What is the probability a fbt will fix it??

thx