Zenith System 3 acting up

[TUD1]

I watched my Zenith System 3 set that I got from an estate sale a few months ago for about half an hour today, and unfortunately, it started acting erratically. The picture will slowly and erractically start to get dim and then it will snap back to normal, and sometimes it will cut off completely for very brief intervals, lasting less than a second. I love this TV, and would be devastated if it broke. The picture is just outstanding, and it's a remote set.

[Findm-Keepm]

Model number or the module complement?

http://www.videokarma.org/showpost.p...65&postcount=1

[zeno]

Start at 9-155-01 CRT socket. See the big flat pack of resistors ?
Check PC under that. Also the rest of the board.
It can also be on the 9-160 or 9-152.
Dont think this had it but the next chassis had a double sided PCB
for the customer controls that caused it also.
While you are in there change the 10mfd 315V cap at the right rear
of the 9-160. You may want to check the PC cons on the
whole board but its been replaced so probably OK.

73 Zeno
LFOD !

[TUD1]

Model No. SY1973P. Sam's is 2193-2.

[Zenith26kc20]

Can't really remember if this set had the small control board (bright, contast, color tint) in front but if it does, look for bad solder joints on it.
Also, tap the chromacolor switch (rectangular switch that goes yellow green or orange when depressed) and see if it causes your problem. It gets dirty for scant usage and can give the problem you describe.
TriFocus tubes ALWAYS look great!

[Findm-Keepm]

...and just to add that in addition to the thin film power resistor (between the output transistors on the CRT board) Zeno mentioned, some CRT boards had a 1/2 watt 1K resistor in the G2 circuit - it'll be on the left of the CRT board looking from the back. Anyway, that 1/2W resistor will increase in resistance or open intermittently, causing loss of G2 voltage and dim pix.

[TUD1]

I watched the set again today with the Color Sentry ON, like I usually do, and the problem was not present. I wonder if it only happens when Color Sentry is OFF?

[Findm-Keepm]

IIRC, Color Sentry changes the color/tint and other controls to another set of servicer adjusted controls - kind of a "get it back to normal, should the kids mess with it" kinda thing. Most have concentric controls - where you can run a 1/8" shaft straight slot screwdriver into the hollow shaft of the control to access the Color Sentry controls. Some also have the photocell that brightens/darkens the pic when the room lighting is adjusted - that comes on when Color Sentry is on.

Just about every manufacturer did it that way - Motorola had the "Instamatic" button, RCA had the "ACC" or AccuColor" button.....

[Jon A.]

Originally Posted by TUD1

I watched the set again today with the Color Sentry ON, like I usually do, and the problem was not present. I wonder if it only happens when Color Sentry is OFF?

Not necessarily. As I re-cap my Electrohome, the random picture dimming problem hasn't yet gone away, it just happens more randomly. The "Auto" button often helps when it's at its worst.

Whatever the cause is, I'm going to be having a solder fest at the CRT neck board as part of the restoration.

[zeno]

IIRC the color sentry put the light sensor on & locked the color tint & contrast.
Again IIRC the presets are separate on these. Marked BL, T & C at the
customer controls. This is a Y line set & thats when they introed the
double sided control board on the cheap "Custom" series 9-181 sets so it
may have one.

CHROMATC turns off all the controls & turns on Auto Tint Guard. Controls
are through the center of the customer controls.
Yes I have seen a few noisy switches on those.

This set is a perfect candidate for tapping around lightly to find
the problem

73 Zeno
LFOD !

[TUD1]

I watched the set for three hours today, and the problem still did not exhibit itself. Knock on wood.