Zenith console

[sampson159]

great,great sets!we sold a lot of those back in the mid to late 70s at the shop.always the best picture and the chassis s were bulletproof!love to have one for myself!

[DaveWM]

the screen brightness flickes somewhat. comes and goes (periods of no flicker the flicer). I assume this could be the HV regulation? or I suppose a dirty pot noisey resistor in the brightness control circuit.

I have tried cycling the brightness control. and the brightness range.

[ctc17]

Mine does the same thing. Mostly one scenes with lots of brightness changes and motion.

[DaveWM]

funny how our two are so much a like. I wonder if a recap would make any changes, I don't really want to since its cool that it has all orig parts and still works so well. I almost think that a recap would simply be putting in cheaply made parts that will not last as long as the remaing life of these old parts.

[old_tv_nut]

Not actually knowing what contributes to high voltage instability, my order of attack might be 1) caps in the regulator circuit; 2) high-value resistors in the regulator circuit.

Anybody with experience of what typically causes such flickering, please chime in.

[DaveWM]

I would like to monitor the HV but think I would need a scope to see if it is the cause. My guess is my analog meter HV prob would be to slow and damped to see it.

I am going to try a few other things, for starters I plan to pull the IF lead form the tuner to get a blank raster. if it still flickers I will put the scope on the crt and check the bias to see if any thing there is going on.

maybe I could use the HV prob in current read mode and use it in series with the scope?

[ctc17]

Iv had my fill of this thing. The vertical jitter is the most annoying then there is there is the brightness flicker. Besides those annoyances its got a good picture.
To look at the hv on my scoped, i would put about a 27k resistor in parallel with the scope, connect the ground lead from the probe to the scope then the scope to ground so you are measuring the drop across the 27k resistor using the probe as your high meg series resistance.

Its going back in the barn and then next one is coming in. Maybe the ctc68 or another zenith multi state. I also got that philco roundie i need to get going.

[DaveWM]

I will keep futzing around with it, if I find out anything I will post.

the vert shakes and the flicker seems to come and go.

I am going to try some tube tapping, and then look into parts around the regulator circuit and the vert. Will also check the pincushion cap on the grid of the pin cushion tube.

[ctc17]

on the x1c38 you can pull the regulator tube and it will just go to max, i dont know on the y1c. It typically only floats up a few k so long as the brightness is up.

The regulator works by loading down the 900volt boost, loading down a low voltage winding on the flyback.

Ill pull mine when i get home and see what it does.

[DaveWM]

just read in the service manual from zenith that jittering vert could be due to a faulty service switch (the one I tried cycling several times) said something about making an "air connections" I assume they mean to just jumper it, also said meter may not see the resistance, therefore the recommedation to "air connect".

there was also talk about a diode/resistor combo to increase convergence range that I may look into (the right side is still just a bit out).

Lastly I think I will check on the cap that is connected to the pincussion coil. No mention of a problem but since its a tuned circuit I was thinking that maybe a out of spec cap may account for the lack of adjustment range, although its more like a lack of amplitude than freq since I can see the center widen to a point but then it starts to shrink back before its completly flat.

I am going to study that pin cushion circuit a few more times to see if I can get my head wrapped around it.

[ctc17]

My tint control is maxed out counterclockwise, where is yours? I pulled the hv regulator tube and it did nothing for the brightness flashing. Pulling the tube out the hv goes form 25 to 27kv at normal brightness and up to 30kv with the brightness at minimum.

[DaveWM]

almost fully counter clock I would say about 10 degrees away.

[DaveWM]

I wonder if C129 the .01 cap that couple the hue pot to the L26 off the burst amp could be an issue?

[DaveWM]

ok finally got around to replacing the pin cushion tube. I tried a couple 6KT8's

one was an Elmento brand and very tall, it had a perfect pincushion correction but then I got some retrace lines when dark screen was present. I tried a shorty 6KT8 and the retrace was gone but the pin cushion was still slightly there. Guess I am going ot have to try a few more.

For you guys that used to service tv back in the day, was it common to have to try a few different tubes to get one to work? both of the tubes I tried were NOS.

[DaveWM]

oh and the vertical and flicker seems to have resolved, I guess just running if for a while may have driven out moisture or pehaps reformed a cap somewhere.

There was a slight ringing in the pix (right side brightish outline) that I got rid of by going thru the IF tubes. I was checking and subbing until I got to the 3rd IF which tested with shorts. I confirmed that the new tube did not have shorts and I tested the bad on two different testers (hickok 533 and a dyna quick). Replacing that tube did the trick no more ringing.

The other tubes tested just in the ok range, but a sub did not seem to improved the pic so I put the orig back in.


I assume the short was causing some oscillations in the IF circuit.

I should have check the signal with my scope, I would have liked to have seen what a ringing signal looked like. I would have put on a test pattern and then started at the grid of the 1st IF tube. I already chucked out that tube so too late to try it now.