Picked up and Admiral 20X122

[Electronic M]

If there is horizontal sync noise in the vertical that might cause it to freak out that way, but if it is just a weak sync problem then you should be able to get a slowly floating near synched picture with the vertical hold control.

No harm tuning the sync up, but if all component values in the vertical are correct and it is still doing that you will probably need to turn to decade box engineering.

[Kevin Kuehn]

Maybe you could try comparing the vertical cap values listed in Sams with those in Riders TV4. The ETF has both schematics available for download.

[Doug66]

I've gone thru both suggestions. I printed out the Riders schematic and compared it to the Sams in both the vertical and sync circuits with no differences.

I do have a capacitor & resistor substitution box like Electronic Memory suggested. I subbed the caps in the vertical circuit and even did some experimenting with the box like changing a .1 to a .01. Nothing cleared up the vertical oscillator.

Here are 3 pics at various settings of he vertical hold control.

[Doug66]

I just replaced the last of the resistors in the sync circuit, and no change. I even disconnected the replacement vert osc transformer and swapped the wires to make sure I hadn't hooked it up backwards.

I have checked and rechecked my work from the 12AU7 sync amp, thru the sync clipper and thru the vertical amp tube and all parts are correct. The only voltage difference is on pin 1 of the vert am. I should have between 80 nd 148 volts, and I have 44. As of now, I've done all I know to do.

[Radiotronman]

I had the same problem on my RCA 721ts I just finished. It turned out to be a dirty vertical hold control. Spray it with contact cleaner and rock vigorously from one end to the other.