Zenith Console combo

[DaveWM]

getting better now, see the thread on the tuner.

next up I need to fix up the channel indicator (cracked) super glue and nylon tread should fix the cracked shafte housing.

the CRT brightness changes from top to bottom, dark at top brighter at bottom. I notice it the most in letter box format.

its as if the video signal is losing contrast as it nears the end of the vert sweep.

I have not checked any tube other than the IF and RF, and this happens regardless of the video source from the tuner or the direct IF feed.

Its like the vert blanking resets the tube.

[DaveWM]

Since I have a very another tube chassis zenith (20yc130) which is nearly the same, I decided to scope the video signal at the video amp transistor collector and the grid of the video output tube. Just to see how it should look when there is a signal. I prob should have check the videok cathode follower (6KT8) but its getting late so need ot knock off and resume tomorrow.

I also checked the agc on the working zenith so see how much hash is ok on the AGC line. Should be very little and it was. This set (the 20x, not the 20y) is VERY sensitive on the AGC setting from blank to loss of sync in only a few degrees of rotaion of the pot. I have a feeling the AGC is still not right. I dont think it should be that critical.

there are a couple 6KT8's so I wil be checking subing etc... the other is for the syn amp.

[DaveWM]

so anybody run into the screen that loses contrast toward the bottom of the screen (a progressive loss from top to bottom).

just hoping to get some pointers..

[DaveWM]

went out to hook up the scope and start trouble shooting the pic issue, power up, PERFECT pic.

the only thing I did was attach a lead to pin two of the video amp.

So I will clean up the garage, button up the back and get a pic.

Not sure why but I aint complaining.

the vert is a tiny bit jumpy, not as bad as my other zenith 20y chassis.

So now I will need to decide if I should pull the chassis or not.

the only issue I have is I know about those old paper caps HV hard shell tube caps. I am tempted to leave well enough alone as I know there is always a risk when disconnecting old plugs etc.. that something could break.

So I will button it up, get some pics, see if the picture contrast at the bottom of the tube returns and see if the vert jump settles down.

The picture color and focus is excellant. Needs a slight dynamic convergence adj. I may replace the diode pack on the board just because its old and I assume the Se's are getting leaky.

one of the reasons I want to pull the chassis is its just so damn dirty, WAF comes into play (if she happens to catch me with the back off, and its in the house).

[DaveWM]

disconnect lead get ready for pics, turn on set, contrast problem has returned.

turns out the video amp tube must have a dirty socket issue, wiggle that vert amp tube and all good again. I guess I was on the right track to check there 1st

Just another reason to pull the chassis and do a though cleaning, including the sockets.

[DaveWM]

the AGC seems to have a bit too much AC ripple in it, no hash but ripple.

Not sure if that could account for the overly sensitive AGC adj. Anyway I will end up pulling the chassis and checking all the filter caps. No audio hum and no hum bars in the pic. I should check the B+ for ripple before I pull it out, IIRC there is a big power resistor that sits on top of the chassis, one side of which connects to the choke and is where they sams show the ripple (2v).

[DaveWM]

some pics, the last two show the need for a lin adj and the pie crust effect that happens when the yoke is squealing, only last for a few seconds. I need to check purity so when I do that I will make sure the screws on tight that holds the yoke in place.

the pie crust is on the last shot of the womens face