"Meat Plow" wrote in message
...
On Mon, 17 Aug 2009 06:18:32 -0500, "Mark Zacharias"
wrote:

"Sylvia Else" wrote in message
.. .
Bob Larter wrote:
Sylvia Else wrote:
Bob Larter wrote:
TonyS wrote:
Bob Larter wrote:
Sylvia Else wrote:

Accumulated dust &/or smoke on the EHT circuitry & the back of the
CRT. Take the back off the TV & see if you can see any arcing.


I would. It most likely needs nothing more than cleaning out all
the
gunk.


It's been a long time since I fixed my CRT TVs. But, wasn't it that
the picture expanded when the HV briefly collapsed when arcing? I
can't see this happening in the video.

I would expect the image to shrink horizontally &/or lose brightness
during arcing.


I think there is an, albeit slight, reduction in width. Whether the
brightness drops is hard to say because the colour disappears.

What I find striking is that some scan lines appear to start early, by
an amount of time that is quite consistent.

It's not clear to me whether the noise is coming out of the
loudspeakers, or directly from the interior of the TV.

Try muting the sound then listen for the noises. If it's audible at
all,
arcing tends to make a hissing or crackling noise.


Does muting kill the power to the audio output amplifier, or just its
audio input?

Sylvia.


He meant to listen to whether any sound could be heard from inside the
cabinet, with the volume down (or muted), not from the speakers.

To answer your question, muting is usually accomplished by means of a
transistor placed across the input of the audio amp circuit. When turned
ON,
the transistor essentially shorts the input of the amp to ground.
Sometimes
a relay is used at the output of the audio amp to open the amp from the
speaker load, although I haven't seen this done on televisions, only on
larger audio amps.

Mark Z.

Isn't lifting the load from a high power audio amp asking for trouble?


Not for a solid state amp. Besides, we're talking about a television audio
amp IC. Hardly high power. Virtually every audio amp or receiver over 40
watts per channel made since around 1970 uses one or more relays to control
the output or protect the speakers in the event of a malfunction.

Mark Z.