I inherited Grandma's old Zenith TV set from the early 80s and for the most
part it works like new. However, sometimes when you first turn the set on,
or maybe after a few minutes of use, the picture will turn to snow and
static on every channel. It will stay like this for anywhere from a few
seconds to ten minutes, and then will snap out of it. After this the TV set
will work fine, with no problems whatsoever, until you turn it off and let
it sit for a while. Then it may or may not come back.

I believe there is an intermittant component somewhere that is causing this;
maybe a faulty varistor that won't work properly unless it's at a certain
temp. My belief that this problem lies somewhere in the RF stages, since the
display and audio are fine.

Where would I begin to look for trouble on this set?

I have extensive knowledge of vacuum tube devices, but transistors and
smaller are unfamiliar territory to me.



Regards,

Tim

Tim R. wrote:
I inherited Grandma's old Zenith TV set from the early 80s and for the most
part it works like new. However, sometimes when you first turn the set on,
or maybe after a few minutes of use, the picture will turn to snow and
static on every channel. It will stay like this for anywhere from a few
seconds to ten minutes, and then will snap out of it. After this the TV set
will work fine, with no problems whatsoever, until you turn it off and let
it sit for a while. Then it may or may not come back.

I believe there is an intermittant component somewhere that is causing this;
maybe a faulty varistor that won't work properly unless it's at a certain
temp. My belief that this problem lies somewhere in the RF stages, since the
display and audio are fine.

Where would I begin to look for trouble on this set?

I have extensive knowledge of vacuum tube devices, but transistors and
smaller are unfamiliar territory to me.



Regards,

Tim


Take off the cover and turn the set on in a dark room. Watch for corona
discharge around the high voltage section and picture tube.

--
The e-mail address in our reply-to line is reversed in an attempt to
minimize spam. Our true address is of the form .

Y'know, now that you mention it, the pitch of the flyback does change in
frequency every once in a while when the set's first turned on, but I never
thought anything of it.

Regards,

Tim


"CJT" wrote in message
...
Tim R. wrote:
I inherited Grandma's old Zenith TV set from the early 80s and for the
most
part it works like new. However, sometimes when you first turn the set
on,
or maybe after a few minutes of use, the picture will turn to snow and
static on every channel. It will stay like this for anywhere from a few
seconds to ten minutes, and then will snap out of it. After this the TV
set
will work fine, with no problems whatsoever, until you turn it off and
let
it sit for a while. Then it may or may not come back.

I believe there is an intermittant component somewhere that is causing
this;
maybe a faulty varistor that won't work properly unless it's at a
certain
temp. My belief that this problem lies somewhere in the RF stages, since
the
display and audio are fine.

Where would I begin to look for trouble on this set?

I have extensive knowledge of vacuum tube devices, but transistors and
smaller are unfamiliar territory to me.



Regards,

Tim


Take off the cover and turn the set on in a dark room. Watch for corona
discharge around the high voltage section and picture tube.

--
The e-mail address in our reply-to line is reversed in an attempt to
minimize spam. Our true address is of the form .

The pitch change means nothing but a slight loading of that circuit, or
loss of incoming sync. If the flyback was not working you would have no
raster, which you have because of snow, plus the high voltage is okay.
The presence of snow, and white noise in the audio indicates everything
after the tuner is working, that the IF circuits are working full gain
with no AGC from incoming signal. You are probably right in your first
thoughts, it is in the RF selector, the tuner. Check supply voltage to
it, also, if possible, remove it as a unit and carefully solder all board
connections with a quality iron... you might fix a bad solder joint, not
an unusual fix for that kind of problem. If possible, flex the board when
the problem is there and see if it produces any change. If so, go after
with the iron.

Thank you.

I'll do as you suggested. I've dealt with bad solder joints before and they
are an often overlooked problem.


"rpbc" spicer_17@protected .com wrote in message
lkaboutelectronicequipment
..com...
The pitch change means nothing but a slight loading of that circuit, or
loss of incoming sync. If the flyback was not working you would have no
raster, which you have because of snow, plus the high voltage is okay.
The presence of snow, and white noise in the audio indicates everything
after the tuner is working, that the IF circuits are working full gain
with no AGC from incoming signal. You are probably right in your first
thoughts, it is in the RF selector, the tuner. Check supply voltage to
it, also, if possible, remove it as a unit and carefully solder all board
connections with a quality iron... you might fix a bad solder joint, not
an unusual fix for that kind of problem. If possible, flex the board when
the problem is there and see if it produces any change. If so, go after
with the iron.

Tim R. wrote:
Y'know, now that you mention it, the pitch of the flyback does change in
frequency every once in a while when the set's first turned on, but I never
thought anything of it.

Regards,

Tim


No guarantees, but that's where I'd start.


"CJT" wrote in message
...

Tim R. wrote:

I inherited Grandma's old Zenith TV set from the early 80s and for the

most

part it works like new. However, sometimes when you first turn the set

on,

or maybe after a few minutes of use, the picture will turn to snow and
static on every channel. It will stay like this for anywhere from a few
seconds to ten minutes, and then will snap out of it. After this the TV

set

will work fine, with no problems whatsoever, until you turn it off and

let

it sit for a while. Then it may or may not come back.

I believe there is an intermittant component somewhere that is causing

this;

maybe a faulty varistor that won't work properly unless it's at a

certain

temp. My belief that this problem lies somewhere in the RF stages, since

the

display and audio are fine.

Where would I begin to look for trouble on this set?

I have extensive knowledge of vacuum tube devices, but transistors and
smaller are unfamiliar territory to me.



Regards,

Tim



Take off the cover and turn the set on in a dark room. Watch for corona
discharge around the high voltage section and picture tube.

--
The e-mail address in our reply-to line is reversed in an attempt to
minimize spam. Our true address is of the form .





--
The e-mail address in our reply-to line is reversed in an attempt to
minimize spam. Our true address is of the form .

rpbc wrote:
The pitch change means nothing but a slight loading of that circuit, or
loss of incoming sync. If the flyback was not working
snip

.... a possibility nobody has suggested.


--
The e-mail address in our reply-to line is reversed in an attempt to
minimize spam. Our true address is of the form .

I'm sorry, I thought I read the sound did not work and had white noise in
it too. Since the sound works forget the tuner,it almost for sure is
working properly.

Where should I look, then? A stage before the tuner, perhaps?

Will also try the corona check when I have time to disconnect and remove the
set, as it's a daily player and surrounded by stuff.


"rpbc" spicer_17@protected .com wrote in message
lkaboutelectronicequipment
..com...
I'm sorry, I thought I read the sound did not work and had white noise in
it too. Since the sound works forget the tuner,it almost for sure is
working properly.

On Wed, 29 Dec 2004 01:08:43 GMT, "Tim R."
wrote:

Where should I look, then? A stage before the tuner, perhaps?

There is no stage before the tuner.

Tom


Will also try the corona check when I have time to disconnect and remove the
set, as it's a daily player and surrounded by stuff.


"rpbc" spicer_17@protected .com wrote in message
alkaboutelectronicequipment
.com...
I'm sorry, I thought I read the sound did not work and had white noise in
it too. Since the sound works forget the tuner,it almost for sure is
working properly.