Picked up and Admiral 20X122

[Doug66]

I finally got a picture this morning. A 75K ohm resistor in the horiz osc circuit was open. I'm getting a good pic now but with vertical issues. It looks like I'm getting a double pic and it will not fill the screen vertically. I'll keep poking at it.

[Kevin Kuehn]

Originally Posted by Doug66

I finally got a picture this morning. A 75K ohm resistor in the horiz osc circuit was open. I'm getting a good pic now but with vertical issues. It looks like I'm getting a double pic and it will not fill the screen vertically. I'll keep poking at it.

Your actually not too far from the correct vertical height. Keep in mind that the top and bottom of the CRT should be covered by the mask for a 4:3 aspect ratio.

[Doug66]

What I seem to have, I think is called Vertical Flopover. You can tell from the pic, that the man's head is at the bottom of the screen while his chest is at the top. Is this a vertical problem or a sync issue? When I 1st turn it on, the horiz will not sync either, and have to adjust the horiz frequency. Now, pin 1of the 12AU7 Vertical Amp should have between 80 and 148V. I only have 38V.
That pin goes to one side of the Vert Blocking Osc Transformer. Pine 2 goes to the other side and the voltage is ok.

[Electronic M]

Your vertical osc is running at double frequency. I've dealt with a set with that issue before.

[Doug66]

I just replaced the vertical osc transformer and all of the resistors in the vertical circuit. Nothing has helped. Vertical osc is still running at twice the frequency. All voltages are fine except pin 1 of the vertical 12AU7. I should have around 90V and I only have 43. Only thing going to that pin is one side of the vert osc transformer.

What would cause it to run at double frequency?

[Electronic M]

Did you accidentally replace a cap with one 10X or 0.1X rated value?....That would do it.

[Doug66]

I just finished replacing the vert height control and the last mica cap in the vert circuit. This made no change. Vert osc still running too fast. I check all caps, and they are correct. I'm at a loss now of what to do next. Any ideas?

[Electronic M]

My case (1953 Zenith) was likely caused by a bumblebee cap being listed a power of 10 off in the schematic VS the parts list of the sam's. I did not have other caps at the time, but did have resistors, and a resistance decade box....I decade box engineered my way out of that mess, and you can too.

[Doug66]

I'm being to thin it's a sync issue instead of a vertical issue. As I noted sometimes when I 1st power on, the horiz will not sync until I adjust the horiz freq at the back of the set.

I use a copy of the 1956 edition of Sams Television Servicing Guide. It called that symptom of he vertical osc running too fast as "Vertical Flopover" and it's listed in the chapter dealing with sync problems.

I checked voltages on the 12AU7 sync amp tuibe. Plate, Pin 1 SB 38 V. I have about 150, and pin 2 SB -1.5. I have about -10. This is with a signal applied. With no signal, the voltages are correct. The .05 cap between pin1 and pin 8 (which is also off) has been replaced, but I put another one in tonite just to make sure. I did the same with the .01 coming off pin 2.

[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.

[Electronic M]

If it ain't dirty controls, then it's probably time for some decade box engineering....Don't worry if you've never done it before, I never did it before when I used it to fix my set, and I managed to figure it out (back in highschool).