RCA 21T9236 (KCS122E) - Repeating skewed trapezoid image

[AppliedTech]

Greetings, new to TV repair just done a couple tube radios. Guessing here, but this seems like a question about geometry adjustment but may be a symptom of a bad tube or something more seriously wrong.

I'm working on a 1958 RCA 21T9236 (KCS122E) I picked up at an estate sale. The video out/horizontal/vertical tubes were all missing, and the rectifier 5U4G was shattered still in its socket. No marks around flyback and transformer but a pool of wax and melted/blown caps on the video, vertical and horizontal boards and electrolytics were no good. There were signs of a couple repair jobs and caps of all ages, who knows how much fiddling has already been done. Recapping everything non-mica and replacing the missing or broken tubes led to noisy static and a heavily skewed repeating trapezoid image after feeding the antenna through a matching transformer from a converter box. At this point I injected component video and audio to bypass the tuner so now the sound is clean and the trapezoid is still there but was crisp enough to read the title card for "Monty Hall" sideways in the slanted image.

So at this point vertical locks with a wide range of give or take on the knob, but horizontal barely locks into this steeply skewed repeating trapezoid image. Rotating the yoke only made the raster rotate but didn't impact the trapezoid. Reading the copy of SAMs I have for it I'm not sure if this is "poor vertical linearity or foldover" and so maybe I need to replace the vertical tubes, or just don't know how to adjust the geometry. Searching through various forums came across some mention of the wrong tube in use, but have checked them all and their labels match the schematic.

Attached is a picture, would someone be able to help identify what this type of problem is called and what's typically the solution?
Video: https://youtu.be/yGBZgebYuv8

Side note, it is also overshooting the screen size and I need to shrink the width/height. Before getting to that I had to shut it off because there were a couple blue sparks in the tube (overshooting the phosphor?) and heard some scary ticking glass sound similar to cracking ice if you've ever walked onto a frozen pond.

[kvflyer]

It appears that the horizontal frequency is off. Have you adjusted the Horizontal Hold control? If so, did it do anything like make less or more lines?

[kvflyer]

BTW, It is close!

[Phil]

Your horizontal freq. is off. Adjusting the horizontal "hold" should straighten up the picture. Overshooting the screen is called "overscan" and is done on purpose on CRT televisions. You may have some dirt in the high voltage cage causing arcing, which creates a sound not unlike your description. Good luck with it!

[Electronic M]

Originally Posted by AppliedTech

Greetings, new to TV repair just done a couple tube radios. Guessing here, but this seems like a question about geometry adjustment but may be a symptom of a bad tube or something more seriously wrong.

I'm working on a 1958 RCA 21T9236 (KCS122E) I picked up at an estate sale. The video out/horizontal/vertical tubes were all missing, and the rectifier 5U4G was shattered still in its socket. No marks around flyback and transformer but a pool of wax and melted/blown caps on the video, vertical and horizontal boards and electrolytics were no good. There were signs of a couple repair jobs and caps of all ages, who knows how much fiddling has already been done. Recapping everything non-mica and replacing the missing or broken tubes led to noisy static and a heavily skewed repeating trapezoid image after feeding the antenna through a matching transformer from a converter box. At this point I injected component video and audio to bypass the tuner so now the sound is clean and the trapezoid is still there but was crisp enough to read the title card for "Monty Hall" sideways in the slanted image.

So at this point vertical locks with a wide range of give or take on the knob, but horizontal barely locks into this steeply skewed repeating trapezoid image. Rotating the yoke only made the raster rotate but didn't impact the trapezoid. Reading the copy of SAMs I have for it I'm not sure if this is "poor vertical linearity or foldover" and so maybe I need to replace the vertical tubes, or just don't know how to adjust the geometry. Searching through various forums came across some mention of the wrong tube in use, but have checked them all and their labels match the schematic.

Attached is a picture, would someone be able to help identify what this type of problem is called and what's typically the solution?
Video: https://youtu.be/yGBZgebYuv8

Side note, it is also overshooting the screen size and I need to shrink the width/height. Before getting to that I had to shut it off because there were a couple blue sparks in the tube (overshooting the phosphor?) and heard some scary ticking glass sound similar to cracking ice if you've ever walked onto a frozen pond.

Your horizontal frequency is wrong. RCAs typically had a hold control potentiometer and a horizontal oscillator coil. If the hold won't get it on frequency then center the pot and adjust the coil. There will be a procedure for adjusting it in the service literature.

[AppliedTech]

Thats it on both. So on the ticking sound, when cleaning I had missed that some old wax had dripped onto the HV rectifier tube near the base. Yikes. It sounds happy now and no more spark in the picture either.

Centering the horizontal hold pot and adjusting the horizontal drive definitely helps rotate it some but it maxes out rotating the picture to an angle of about 10 & 4 o'clock.

I'm out of time this weekend, but I'm guessing I'll find a bad resistor(s) on the horizontal printed board that's putting the horizontal outside of the pots. I'll report back, thanks for your help!

[jr_tech]

Can you find a Horizontal Frequency coil/slug to adjust?

jr

[Tom9589]

The horizontal Drive control should have little or no effect on the horizontal frequency. Jr_Tech is correct. Look for the coil to adjust. It should have a much wider frequency range than the Horizontal Hold control does.

[Electronic M]

The drive control is almost always a variable capacitor and typically doesn't adjust the frequency.

The horizontal osc coil usually has 2 adjustable ferrite slugs that set the frequency and waveform of the horizontal osc.

On the RCA synchroguide circuit if it's way out to lunch (which is sometimes exacerbated by a restoration as repairmen may have adjusted it to compensate for a drifting component you replaced) I typically use an oscilloscope to adjust it so that I know the waveform is OK, and so it'll be synched up perfectly next time I install the chassis.
Basically I scope a composite video signal, get 2-3 sync pulses on screen, count the divisions between them, don't touch the timebase of the scope again, scope the horizontal osc in the TV and set the peaks for the same number of divisions separating them and adjust waveform so the peak is slightly higher than the hump.

You can eyeball it, especially when it's as close as you have it, but nothing beats having it set perfectly with the aid instruments.

[AppliedTech]

That did it, thank you all! I went looking for screws, but needed to feed a hexagon alignment tool through the horizontal waveform coil. There was no adjustment available on the horizontal frequency coil. I now have a working picture. Will need to add a photo when around a computer.

[AppliedTech]

Here it is, the picture is stable and it stayed that way for a couple of hours last night using a digital->analog converter, and then an old junker laptop to feed it shows through an HDMI->Composite adapter.


I need to get the mirror back on it and spend some time adjusting it, lesson learned on the coil adjustment locations. Looking back at the SAM's manual with new eyes I see it did clearly identify the location and adjustment methods, but I jumped to the conclusion that they would have flathead screwcaps like my radios. Here's an example picture of what an adjustment for a nylon hex adjustment tool looks like located inside of the coil looks like if another beginner stumbles on it in the future:

[Electronic M]

It's probably easier to spot on the component side of the board.
You're doing better than I did first time I needed to adjust a hex slug...I knew it was a hex slug, but not having the plastic tool and being a broke highschool kid with broke parents in the great recession like an idiot I used a metal hex tool and chipped the end of a convergence slug of a color Zenith...There was enough range to live without the chip, but still I learned that lesson the hard way...

Originally Posted by AppliedTech

Here it is, the picture is stable and it stayed that way for a couple of hours last night using a digital->analog converter, and then an old junker laptop to feed it shows through an HDMI->Composite adapter.


I need to get the mirror back on it and spend some time adjusting it, lesson learned on the coil adjustment locations. Looking back at the SAM's manual with new eyes I see it did clearly identify the location and adjustment methods, but I jumped to the conclusion that they would have flathead screwcaps like my radios. Here's an example picture of what an adjustment for a nylon hex adjustment tool looks like located inside of the coil looks like if another beginner stumbles on it in the future:

[kvflyer]

Not to mention that a metal tool will change the inductance dramatically when inserted, causing changes difficult to make accurately. What stinks is when the slug is stuck and won't move. That can be a pain...