Old Sony KV2781R typical problems
 

I just picked up, from a moving neighbor who left it behind, an old 27"
Sony KV2781R, mfd March 1987. I can't pass up a freebie. When you
push the on-off switch there is a click and a degaussing sound, but
nothing more. Are there any frequent/common problems that I should
look for first. I don't want to rebuild the whole set, but hate to
just add this to the collecting garage in our landfills until I give it
a go. I have a scope, but no schematic for this particular set. Been
doing tv repairs since vacuum tube days, for those of you who remember
what they are. :-)

Advice appreciated.

H. R.(Bob) Hofmann

It is very common that the drive IC in the power supply fails. It runs
fairly hot, and after a while the mounting screw can loosen up, and thus the
IC becomes overheated. I have put small whisper fans in these sets to help
cool down the power supply. If any of the decoupler caps in the drive
circuits start to go high in their ESR, this IC can also be damaged.

It is also best to go through the power supply, vertical and horizontal scan
amplifiers, protection circuits, and check for any high ESR capacitors. The
caps tend to give problems, especially in the older sets.

On the odd occasion, I have had bad flybacks and horizontal output
transistors fail, and also cause damage to the power supply.

Considering the age of the set, and that it has not been used for a long
time, I would expect the CRT to also be very weak.

--

Jerry G.
=====

wrote in message
oups.com...
I just picked up, from a moving neighbor who left it behind, an old 27"
Sony KV2781R, mfd March 1987. I can't pass up a freebie. When you
push the on-off switch there is a click and a degaussing sound, but
nothing more. Are there any frequent/common problems that I should
look for first. I don't want to rebuild the whole set, but hate to
just add this to the collecting garage in our landfills until I give it
a go. I have a scope, but no schematic for this particular set. Been
doing tv repairs since vacuum tube days, for those of you who remember
what they are. :-)

Advice appreciated.

H. R.(Bob) Hofmann

This model was long before the STRS6301 was ever invented. You most
likely have a bad flyback transformer plus shorted horiz output.

RonKZ650 wrote:
This model was long before the STRS6301 was ever invented. You most
likely have a bad flyback transformer plus shorted horiz output.

Oops - you are right! Sorry, I misread the model number sheepish
look.

On 4 Mar 2005 08:12:11 -0800, wrote:

I just picked up, from a moving neighbor who left it behind, an old 27"
Sony KV2781R, mfd March 1987. I can't pass up a freebie. When you
push the on-off switch there is a click and a degaussing sound, but
nothing more. Are there any frequent/common problems that I should
look for first. I don't want to rebuild the whole set, but hate to
just add this to the collecting garage in our landfills until I give it
a go. I have a scope, but no schematic for this particular set. Been
doing tv repairs since vacuum tube days, for those of you who remember
what they are. :-)

Advice appreciated.

H. R.(Bob) Hofmann


The most common problem I see with these is failure of the horizontal
output transistor and voltage regulator (SRT3130, I think). There's a
small capacitor (about .47 uF) near the vertical IC heat sink that's
in the horizontal drive circuit. It fails from heat and causes the
HOT to fail. The flyback can fail, but most just need the cap, HOT
and regulator. Be aware that the CRT is probably not looking its best
anymore. If you can fix it yourself, it might be worth it, but I
wouldn't pay to have it repaired.
Andy Cuffe

-- Use this address until 12/31/2005

-- Use this address after 12/31/2005

Thanks to everyone who posted. I have never in my life paid to have a
tv fixed, starting with when I was in college studying electrical
engineering in 1953-1957. Put myself thru college fixing tv sets. P
I have an original RCA 630ts in my basement that still gets a picture,
that's 55 years old.

Bob Hofmann