I already posted this message under the name "John Wright". Forgive me
if this is a double post, but the newsgroup software or server used on
the other account seems to not be functioning, in that I posted the
message over an hour and a half ago and it has yet to reach the rest
of the world.



Hi there. This television has it out for me.

I recently began work on a Sony Trinitron television, model KV-2782R.
Initial symptoms were that the audio amp would come on (producing
audible
hiss) but the rest of the set was dead. 130V fuse F501 was blown.
Removing
all aux supplies from the flyback (by way of desoldering one end of
components) did not appear to remove the short. Removing the HOT did.
Replacing the HOT did not.

During my attempts to locate the short, power supply "GA" board made a
sizzling noise, then my 130V disappeared altogether, along with the
audio
amp power.. Testing revealed one of the two TO-220 2SC transistors on
said
board was shorted. I replaced this transistor with a substitute
identified
via a website. Upon reapplying power (with the 130V output plug to the
mainboard disconnected), the new transistor shot out a large spark,
the
resistor located between the two transistors (electronically - between
one's
collector and the other's emitter) burned open, and the second
transistor
shorted.

At this point, I replaced both transistors and the resistor, then
tested all
of the other diodes and resistors. I was presented with a power supply
that
would turn on then immediately turn itself back off. I must admit, I
next
did something I shouldn't have - disabled the protection circuit (by
isolating one pin of mainboard D-27). The power supply remained on,
the amp
came to life, and I had 130V. Very shortly thereafter, board GB
emitted a
large quantity of smoke. I have not done anything with it since.

Today, I picked up a KV-2785R, presumed to be working with a minor
tuner
problem, expecting to measure the voltages in the power supply section
in
order to repair the 2782. However, I was disappointed to find that the
2785
has input from the rectifier to the GA board, and some voltage
(apparently -300V? I'm not using my own meter and can't hardly read
the one
I am using!) on its output to the GB board. However, GB has no output
to
power amp or 130V...

What is likely to be fried on the 2782's GB board? I'm hoping to
repair it
with parts from the 2785, then attach it to the 2785's GA board. Yes?
No?

What else might I be looking for that could be causing the 130V short
on the
2782 mainboard?

What voltages am I looking for at the various points throughout the
power
supply block? Specifically, what should be the output voltage of GA,
before
GB. Second, what should be the output voltages of GB?

Lastly, what is the purpose of these two boards? They are obviously
some
form of SMPS, yet I certainly cannot see any isolation on GA, and
haven't
tried to follow GB yet. GA APPEARS to invert the polarity of its
input. No?

I have no service manual or valid information to go on - so any
informative
input is appreciated.

The eventual goal is to have both sets working - but having one
working is
the first step.

These sets are a challenge for any of the service techs, because of their
complexity. The first thing you should invest in is the service manual.
Without the proper Sony training, these sets are even a greater challenge.
Over an email, it will not be possible to give detailed help.

From what you describe, the flyback assy is most likely defective, and there
is most likely missing drive from the scan gen to the horiz output
transistor. The driver transformer also can give problems in this series of
set. If the drive pulses to the horiz output trans are missing, this device
can go short. More than likely there are some capacitors that have become
high in ESR, in the horiz output section, and in the power supply section.
These will cause failures.

You will have to first fix the power supply. You can work on the main
supply with the horiz output trans pulled out. You then must find all the
defective parts in the horiz output stage before re-applying the power to
the set. If the set does not come on, and there is a short, the new parts
will most likely be failed again. This is instant when there is no proper
start-up, and there is a short in these areas.

I have very rarely seen non trained technicians be able to have success with
these sets when there are complex faults with them. This is the same for
most of this category of TV set, and or monitors.

--

Greetings,

Jerry Greenberg GLG Technologies GLG
=========================================
WebPage http://www.zoom-one.com
Electronics http://www.zoom-one.com/electron.htm
=========================================


"Michael Parker" wrote in message
om...
I already posted this message under the name "John Wright". Forgive me
if this is a double post, but the newsgroup software or server used on
the other account seems to not be functioning, in that I posted the
message over an hour and a half ago and it has yet to reach the rest
of the world.



Hi there. This television has it out for me.

I recently began work on a Sony Trinitron television, model KV-2782R.
Initial symptoms were that the audio amp would come on (producing
audible
hiss) but the rest of the set was dead. 130V fuse F501 was blown.
Removing
all aux supplies from the flyback (by way of desoldering one end of
components) did not appear to remove the short. Removing the HOT did.
Replacing the HOT did not.

During my attempts to locate the short, power supply "GA" board made a
sizzling noise, then my 130V disappeared altogether, along with the
audio
amp power.. Testing revealed one of the two TO-220 2SC transistors on
said
board was shorted. I replaced this transistor with a substitute
identified
via a website. Upon reapplying power (with the 130V output plug to the
mainboard disconnected), the new transistor shot out a large spark,
the
resistor located between the two transistors (electronically - between
one's
collector and the other's emitter) burned open, and the second
transistor
shorted.

At this point, I replaced both transistors and the resistor, then
tested all
of the other diodes and resistors. I was presented with a power supply
that
would turn on then immediately turn itself back off. I must admit, I
next
did something I shouldn't have - disabled the protection circuit (by
isolating one pin of mainboard D-27). The power supply remained on,
the amp
came to life, and I had 130V. Very shortly thereafter, board GB
emitted a
large quantity of smoke. I have not done anything with it since.

Today, I picked up a KV-2785R, presumed to be working with a minor
tuner
problem, expecting to measure the voltages in the power supply section
in
order to repair the 2782. However, I was disappointed to find that the
2785
has input from the rectifier to the GA board, and some voltage
(apparently -300V? I'm not using my own meter and can't hardly read
the one
I am using!) on its output to the GB board. However, GB has no output
to
power amp or 130V...

What is likely to be fried on the 2782's GB board? I'm hoping to
repair it
with parts from the 2785, then attach it to the 2785's GA board. Yes?
No?

What else might I be looking for that could be causing the 130V short
on the
2782 mainboard?

What voltages am I looking for at the various points throughout the
power
supply block? Specifically, what should be the output voltage of GA,
before
GB. Second, what should be the output voltages of GB?

Lastly, what is the purpose of these two boards? They are obviously
some
form of SMPS, yet I certainly cannot see any isolation on GA, and
haven't
tried to follow GB yet. GA APPEARS to invert the polarity of its
input. No?

I have no service manual or valid information to go on - so any
informative
input is appreciated.

The eventual goal is to have both sets working - but having one
working is
the first step.