J
John Wright
Guest
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.
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.