help with Sony XBR power problem

[davexnet02]

Hello all,
Any thoughts on this problem?

The TV is currently disconnected from the power.
If I plug it in you hear the characteristic
power noise; a momentary hum - not sure what you call it,
but it's normal.
However, attempting to turn on the TV using the remote
or the set button does nothing.

After about five minutes, the TV mysteriously
turns on - all is normal for a few minutes and
the TV turns itself off again.

It did this once or twice, and I've had it unplugged
since. Trying to evaluate the situation before doing
anything else.
1992 27 inch Sony xbr.

TIA,
Dave

 

[davexnet02]

Hello all,
Any thoughts on this problem?

The TV is currently disconnected from the power.
If I plug it in you hear the characteristic
power noise; a momentary hum - not sure what you call it,
but it's normal.
However, attempting to turn on the TV using the remote
or the set button does nothing.

After about five minutes, the TV mysteriously
turns on - all is normal for a few minutes and
the TV turns itself off again.

It did this once or twice, and I've had it unplugged
since. Trying to evaluate the situation before doing
anything else.
1992 27 inch Sony xbr.

TIA,
Dave

More info. I have taken out the chassis and I have a
copy of the service manual. I do see one obviously
broken solder joint, but it's in a place that I don't think
is responsible for the problem at hand.
I'm looking at the underside of the A board, towards
the back of the set between where the M and E2 board go.
I noticed a small black area (burned out?) and a broken
connection corresponding to pin 35 (E2) and what looks like
pin 15 on the M side.
It can be seen on page 89 of the kv27xbr35 manual.

Other observations:
The solder at the flyback transformer pins looks a little
dodgy, and I'll probably go over that.
There is a small transformer T503
that sits between the H.out and V.out big heat sinks.
This transformer is coverered with a white, chalky looking
substance. If I pick at it, it flakes off.
Not seen this before - bad?
That's all for now.

Any idea's appreciated.
Dave

 

[Paul of Dayton]

Dave,
Many Sony TV's of that era suffered from poor soldering on the main board.
Poor design contributed since there was a fairly heavy transformer soldered
in that only has the board for support. Carefully resoldering larger
components may cure it. (I can't remember the list of areas to solder
specifically.) My personal experience is with a KV27XBR50 - but details
have become foggy since the set has been fine for years after I soldered it
back together...

I hope this is helpful. PoD

 

[[email protected]]

Dave,
Many Sony TV's of that era suffered from poor soldering on the main board.
Poor design contributed since there was a fairly heavy transformer soldered
in that only has the board for support. Carefully resoldering larger
components may cure it. (I can't remember the list of areas to solder
specifically.) My personal experience is with a KV27XBR50 - but details
have become foggy since the set has been fine for years after I soldered it
back together...

I hope this is helpful. PoD

Thanks for the info. I soldered the heavier components on the main board,
these seem to be in the worst shape. This included the flyback, and the
transistors attached to the heat sinks in the H.out and V.out area's.

I put it all back, but it continues to have a fault. I plug it in, there is
the usual hum-buzz sound. The LED lights at the front/top of the set are
on. I don't remember if this was the case when all was working.
Trying to turn on the set now dosn't work. After a minute or two,
the LED goes out and now the TV can be switched on.
Pressing the "headphone" button on the remote immediately turns off the
TV. Its unstable, and I'm not going to use it like this.

Unfortunately, my favorite TV repair shop in the area no longer do
house calls; which means I'll need some help getting it down there.
This is one heavy TV!
Dave