My family bought this TV new 17 years ago. We never had any trouble with
it until a year ago when it made a loud spark and the picture went blank
momentarily. It did the same thing again several months later. Recently
it's developed a second problem where the picture develops a fog with
about twenty inclined horizontal line segments. The lines start and end
about 1 inch from the left and right edge of the picture, respectively.
They do not move vertically. The fog looks the same as what you would
see if the G2 (screen) voltage were set too high. The picture geometry
and focus look normal. The fog problem never starts until at least 10
seconds after the TV is turned on. Then it usually does occurs, although
it sometimes disappears for a while only to return again. The sparking
problem has increased, but it has only occurred when the fog wasn't
there.

I've tested several voltages in the system, including B+, the regulated
voltage to the Horizontal Output Transistor, the heater/filament, G1, G2
(screen), and the CRT anode. All voltages, except G1, drop about 5%
during the fog. G1, which is about 32v normally, will jump as high as
140v during the fog. The brighter the fog the higher it goes.

I tried disconnecting the power to G1. The fog problem became worse and
the voltage on the G1 pin continued to spike. I then reconnected G1 and
disconnected G2. I was certain that the picture wouldn't appear. I was
wrong. The picture came up and then the fog reappeared. The instant I
touched the terminal pin for G2 with my test lead to test the voltage the
picture went almost completely black.

I've read Sam's guide (thanks for the wealth of info) on TV repair which
lead me to the conclusion that the CRT is shorting. The guide mentions
discharging a capacitor across the shorted components but I'm unsure
exactly what's shorting or how many farads to use. I'm hoping one of you
experts out there can advise me on what to do next. Is there any hope?
Should I pull the plug on this beloved family member for good?

Many thanks,
Scott

What is happening when you simply disconnect the G1 or G2 for that
matter is the pins are left floating inside the picture tube. They
will build up a voltage from the other stay voltages in the tube.

Looks like you need to determine if the excess G1 is due to the picture
tube or circuitry.

Disconnect the G1 and connect it to ground through a one kiloohm 2 watt
resistor, that should be low enough to keep it at or near zero volts
even with the stay voltages. The tube should stay dark during the
entire time unless it has an internal short problem.

Also connected the stray G1 that would have gone to the pin to gorund
through a 47K ohm 1 watt resistor and make sure it does not rise all by
itself. If it does the problem is likely in the circuitry.

If the crt is shorting: where would you guess that a voltage of 140v
would come from?
In other words, what other pins on the crt has a voltage close to 140v?

It is sometimes possible with a crt rejuvinator short removal feature
to blast the short out of the offending location in the guns, but not
always.

After disconnecting G1 the voltage before the break (the flyback side)
remained constant while the voltage after the break (the G1 pin side)
oscillated so I'm sure that the voltage spikes were coming from inside
the CRT.

I considered that one of the cathodes could be shorting to G1 but then
why is the fog white instead of some other color? Also, I happened to
have my voltmeter on G1 during one of those sparks and the meter read
full scale - well over the normal voltage of the guns.

I will try grounding G1 as you suggested. Thank you very much for your
help.

Scott



" wrote in
ups.com:

What is happening when you simply disconnect the G1 or G2 for that
matter is the pins are left floating inside the picture tube. They
will build up a voltage from the other stay voltages in the tube.

Looks like you need to determine if the excess G1 is due to the picture
tube or circuitry.

Disconnect the G1 and connect it to ground through a one kiloohm 2 watt
resistor, that should be low enough to keep it at or near zero volts
even with the stay voltages. The tube should stay dark during the
entire time unless it has an internal short problem.

Also connected the stray G1 that would have gone to the pin to gorund
through a 47K ohm 1 watt resistor and make sure it does not rise all by
itself. If it does the problem is likely in the circuitry.

If the crt is shorting: where would you guess that a voltage of 140v
would come from?
In other words, what other pins on the crt has a voltage close to 140v?

It is sometimes possible with a crt rejuvinator short removal feature
to blast the short out of the offending location in the guns, but not
always.

What are G1 and G2 then? Control grids.
Either one or both sets up the baseline drive level for the entire
tube. The fog might be shifted to one color if the cathode is actually
shorting to the G1, but since G1 controls the baseline drive along with
G2 for all the guns, you might not notice it.

Hi, new guy on the block. If i may' I'd suggest trying to locate a crt
brightener and install it. Heater to cathode shorts are common and the
xfrmr that steps up the heater voltage will also act as an isolation
xfrmer. Also agree with the rejuvenator with short repair feature to
blow out the offending residue between elements.

Frog

Hi, new guy on the block. If i may' I'd suggest trying to locate a crt
brightener and install it. Heater to cathode shorts are common and the
xfrmr that steps up the heater voltage will also act as an isolation
xfrmer. Also agree with the rejuvenator with short repair feature to
blow out the offending residue between elements.

Frog

Why would one install a heater to cathode isolation to try and 'fix' a
possible cathode to G1 short?

frog wrote:
Hi, new guy on the block. If i may' I'd suggest trying to locate a crt
brightener and install it. Heater to cathode shorts are common and the
xfrmr that steps up the heater voltage will also act as an isolation
xfrmer. Also agree with the rejuvenator with short repair feature to
blow out the offending residue between elements.

Frog

Heater to cathode short would affect just one cathode, not all three
simultaneously.

John

True. I didn't think thazt one through as I should have.

I tried disconnecting the red and surprisingly the problem stopped. I
reconnected it and it's still working okay, though I'm sure it's just a
matter of time. When the problem returns I will try grounding G1 through a
47k resistor to confirm that the tube is shorted, as dkuhajda recommended.
And if it is then I'll try zapping G1 and the red cathode and then give it
its last rights. At least I'll know that I did everything I could for it.

Thank you everyone for helping me out.

Scott