Newbie's First Questions RCA TS 721 Restoration

[Kevin Kuehn]

Originally Posted by Chris K

128C is an electrolytic...130uf. Now there is a possible issue there as I have a 220uf electrolytic there. I didn't want to assemble a 100uf and 47uf pair because I had a high quality 220uf cap operating off the assumption going a bit bigger with an electrolytic didn't matter. I guess that's true for AC filtering but I'm not so sure now about using it in this circuit. What does team "Help Chris" think?!

I do believe the 220uf cap could be upsetting the vertical linearity. I tried something similar on my Zenith Bug eye and chased my tail for a few hours. My understanding is it's not intended as a complete bypass.

[Chris K]

OK I'll pull the electrolytic and change the pots for linearity and height. I got the 5K pot for VL from the parts chassis and it works fine with a smooth ramp from 0-5K ohms. I didn't change anything last night, turned the TV on and the horizontal was out of whack. Couldn't get it to lock. I think I'll wait for the oscilloscope and start looking at waveforms at the test points going through it systematically.

[Chris K]

VL pot is bad...0 ohms...replacing with one from the parts chassis.

[Chris K]

Originally Posted by Chris K

VL pot is bad...0 ohms...replacing with one from the parts chassis.

220uf capacitor replaced with a 147uf "combocap" and vertical linearity pot changed. I don't know if I should laugh or cry. It's obvious I need to start with the basic waveforms when the scope comes. I call it abstract TV art!

[Kevin Kuehn]

Originally Posted by Chris K

220uf capacitor replaced with a 147uf "combocap" and vertical linearity pot changed. I don't know if I should laugh or cry. It's obvious I need to start with the basic waveforms when the scope comes. I call it abstract TV art!

What is that test pattern supposed to be?

[Chris K]

Originally Posted by Kevin Kuehn

What is that test pattern supposed to be?

Crosshatch

[Chris K]

Originally Posted by Chris K

Crosshatch

Getting somewhat better. I think I have a vertical issue. Horizontal doesn't seem too bad.

[old_tv_nut]

Definitely need to fix the vertical first, then you can see if the horizontal is totally OK.

[bandersen]

Is the set lying on its side? If so, the horizonal frequency is way off.

[Chris K]

Originally Posted by bandersen

Is the set lying on its side? If so, the horizonal frequency is way off.

No but, the photo is rotated 90 degrees to the left so same thing. Is the horizontal frequency adjusted via L121 or by the trimmer on the back of the chassis labeled "Horizontal Frequency"...C136A I believe...or both?

[bandersen]

Both. L121 is the coarse adjustment, C136A is the fine adjustment. Start with C136. If that does get you a locked image, put C136 mid range and adjust L121

[Chris K]

Originally Posted by bandersen

Both. L121 is the coarse adjustment, C136A is the fine adjustment. Start with C136. If that does get you a locked image, put C136 mid range and adjust L121

OK thanks Bob...I'll give that a try. I with I had one of those 5" serviceman's tubes. It's a real pain turning this chassis on its side with an unsecured, full size CRT in it. I made a plywood, curved cradle to hold it in position when it's upright but, other than piling towels under the tube to hold it positioned in place, there's no convenient way to access the bottom of the chassis to do adjustments with a displayed picture.

[Chris K]

Originally Posted by bandersen

Both. L121 is the coarse adjustment, C136A is the fine adjustment. Start with C136. If that does get you a locked image, put C136 mid range and adjust L121

Getting somewhat closer. Why is so much of the image bunched up at the top? This isn't a vertical issue? The set is on its side but the image is rotated so it is displayed in the right orientation.

[bandersen]

I'd say a lot closer Yes, it is a vertical issue. Looks like foldover and you have way too much height. Remember the viewing area is a 4:3 aspect ratio rectangle - it's not a porthole set. You should have about 1-1/2" blank at the top and bottom.

Reduce the height and adjust the vertical linearity and see where that gets you.

[Chris K]

Originally Posted by bandersen

I'd say a lot closer Yes, it is a vertical issue. Looks like foldover and you have way too much height. Remember the viewing area is a 4:3 aspect ratio rectangle - it's not a porthole set. You should have about 1-1/2" blank at the top and bottom.

Reduce the height and adjust the vertical linearity and see where that gets you.

Hey there...I've tried dozens of adjustments and combinations using the vertical linearity and height. The image is centered as per the dot in the middle of the crosshatch. One observation, the height pot is very sketchy. The deflection collapses with a tiny turn and then resets. I do have a spare height pot. Maybe the pot is bad? I've already replaced the linearity pot which was very bad. Would a bad height pot possibly account for the top and bottom folds?