Hi everyone,

I've got a sod of a TV set here which is puzzling me and I hoped that
someone here more knowledgable than myself might be able to offer
some advice.

It uses the L01.1E chassis and is a 32" widescreen. Originally it was
tripping which turned out to be S/C line output transistor (or HOT as
some call it), probable cause being C2455 (47uF/25V) in the line
driver circuit, low in value at 36uF. This is apparently the usual
cause with this chassis, and there is also a PSU kit available for
the SMPS in the event that the set continually kills the line output
transistor.

Anyway, replaced the transistor (BU4508DX) with a BU2508DF and
replaced the cap with the only available one (47uF, 63V). The set now
comes on. I don't know if it's usual behaviour for this set, but it
takes a while for the raster to appear, during which a couple of
relays click. After 2 or 3 seconds or so, the set then shuts down. It
seems the line drive is taken away when this happens, as the HT line
rises from its value of 126V under load, to its 140V unloaded
potential.

Although it shuts down quickly, I found that I could keep it on longer
by going through the channels; it seems to stop the shut-down process.
I brought up a channel with a very good undistorted image, stopped
flicking through the channels, leaving it one this one, and then the
set died after a few seconds as normal. The transistor doesn't seem
to be getting terribly hot during this.

Incidentally, it may just be me, but the line stage doesn't sound
right... the high-pitched noise coming from the LOPT seems to have
harmonics by the way there is a 'flicker' or 'roughness' to it. It's
hard to describe.

Any ideas or suggestions would be much appreciated as this has been on
the bench too long now and I'm tired of its 32 inches taking up most
of the workspace and falling over its gigantic rear cover!

Thanks to all who even read this, and especially to anyone who
replies.

James

Did you look at your HOT drive waveforms? coupling caps, and bypass
caps.
Look for a missing or distorted waveform.

JamesQB wrote:
Hi everyone,

I've got a sod of a TV set here which is puzzling me and I hoped that
someone here more knowledgable than myself might be able to offer
some advice.

It uses the L01.1E chassis and is a 32" widescreen. Originally it was
tripping which turned out to be S/C line output transistor (or HOT as
some call it), probable cause being C2455 (47uF/25V) in the line
driver circuit, low in value at 36uF. This is apparently the usual
cause with this chassis, and there is also a PSU kit available for
the SMPS in the event that the set continually kills the line output
transistor.

Anyway, replaced the transistor (BU4508DX) with a BU2508DF and
replaced the cap with the only available one (47uF, 63V). The set now
comes on. I don't know if it's usual behaviour for this set, but it
takes a while for the raster to appear, during which a couple of
relays click. After 2 or 3 seconds or so, the set then shuts down. It
seems the line drive is taken away when this happens, as the HT line
rises from its value of 126V under load, to its 140V unloaded
potential.

Although it shuts down quickly, I found that I could keep it on longer
by going through the channels; it seems to stop the shut-down process.
I brought up a channel with a very good undistorted image, stopped
flicking through the channels, leaving it one this one, and then the
set died after a few seconds as normal. The transistor doesn't seem
to be getting terribly hot during this.

Incidentally, it may just be me, but the line stage doesn't sound
right... the high-pitched noise coming from the LOPT seems to have
harmonics by the way there is a 'flicker' or 'roughness' to it. It's
hard to describe.

Any ideas or suggestions would be much appreciated as this has been on
the bench too long now and I'm tired of its 32 inches taking up most
of the workspace and falling over its gigantic rear cover!

Thanks to all who even read this, and especially to anyone who
replies.

James