Newbie's First Questions RCA TS 721 Restoration

[Penthode]

I haven't read if the wax capacitors had been changed? I recently restored the same,set and changed most of them. The few I did not change were shunted by resistances much lower than the leakage e.g. 1kohm or 10kohm with leakage about 10Mohm.

The wax capacitors will be all bad. You will have to change pretty well all of them to get it to work.

[Chris K]

Originally Posted by Penthode

I haven't read if the wax capacitors had been changed? I recently restored the same,set and changed most of them. The few I did not change were shunted by resistances much lower than the leakage e.g. 1kohm or 10kohm with leakage about 10Mohm.

The wax capacitors will be all bad. You will have to change pretty well all of them to get it to work.

They're all gone...replaced with good quality Panasonic film caps and I substituted Rubycon electrolytics for all the cans.

[Chris K]

Originally Posted by Notimetolooz

I think that was the major cause of the problem.
Getting pretty close though. The voltages can be off 10% or more and it should work OK.
CRT pin 11 is variable with the control. Pin 10 voltage could be effected by the horizontal sweep performance.
I haven't seen the SAMS, just Rider's.
So what does the screen look like now?

Got it on the Leader....total mess but at the least, I have a picture!!! Now we're back to frequencies. Despite the mess on the screen, I'm so happy the picture is back!!!

Of course, it's rotated 90 degrees left1!!

[Penthode]

Nothing looks wrong with the horizontal sweep. The vertical sweep has severe bottom fold over. Is the capacitor to the 6k6 cathode attached correctly?

I would go through the vertical sweep circuit especially the output as the vertical is at least synced.

[Kevin Kuehn]

Yay. At least it's back from the dead.

[Chris K]

Yes thank goodness...the patient has regained consciousness and is out of the coma. Now the physical therapy can begin. Vertical sweep circuit inspection this evening. Also, the focus is still a bit soft. The focus pot is adjusted to its limit. But I think I want to get a stable image first before I concern myself with tweaking the quality of the picture.

[Chris K]

Originally Posted by Penthode

Nothing looks wrong with the horizontal sweep. The vertical sweep has severe bottom fold over. Is the capacitor to the 6k6 cathode attached correctly?

I would go through the vertical sweep circuit especially the output as the vertical is at least synced.

The 6K6 audio output tube?

[Notimetolooz]

Try adjusting the vertical linearity and height. I doubt that will completely correct the screen but it is a good place to start.
The scope from ebay may get there just in time to help with the vertical problem. There are a few pictures of what the correct vertical waveforms should look like in the Rider's. Notice one waveform is about 750V peak to peak, that could damage some probes or even the scope input itself.

[Chris K]

Originally Posted by Notimetolooz

Try adjusting the vertical linearity and height. I doubt that will completely correct the screen but it is a good place to start.
The scope from ebay may get there just in time to help with the vertical problem. There are a few pictures of what the correct vertical waveforms should look like in the Rider's. Notice one waveform is about 750V peak to peak, that could damage some probes or even the scope input itself.

I did try to adjust both the linearity and height. The linearity was VERY touchy with the collapse of vertical deflection with very small adjustments. Scope due Thursday. I worked on a couple of old 5Mhz Heathkit scopes from the early 1960s and got them running. Would they be of any use?

[Kevin Kuehn]

Originally Posted by Chris K

The 6K6 audio output tube?

I believe he meant to say 6SN7(V107 vert output). The appropriate cap would be C128C.

[Kevin Kuehn]

Originally Posted by Chris K

I did try to adjust both the linearity and height. The linearity was VERY touchy with the collapse of vertical deflection with very small adjustments.

This could also mean a dirty or worn pot.

[Chris K]

Originally Posted by Kevin Kuehn

This could also mean a dirty or worn pot.

I tried...except for the focus pot, they are sealed up tight.

[Chris K]

Originally Posted by Kevin Kuehn

I believe he meant to say 6SN7(V107 vert output). The appropriate cap would be C128C.

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?!

[Notimetolooz]

A 5MHz scope could be used. Up until sometime in the 1970's that is what the repair shops would use. It would certainly be OK for audio or sweep waveforms.

The capacitor may play a roll. However tolerances on electrolytic caps were usually very wide, sometimes -20%/+80%, so they were seldom used if the value was critical. Modern electrolytics can have somewhat tighter tolerances, but still not great.
Of course the tube is also a possibility, as well as resistors.

It does sound like the pot is bad.

[Chris K]

Originally Posted by Notimetolooz

A 5MHz scope could be used. Up until sometime in the 1970's that is what the repair shops would use. It would certainly be OK for audio or sweep waveforms.

The capacitor may play a roll. However tolerances on electrolytic caps were usually very wide, sometimes -20%/+80%, so they were seldom used if the value was critical. Modern electrolytics can have somewhat tighter tolerances, but still not great.
Of course the tube is also a possibility, as well as resistors.

It does sound like the pot is bad.

Ive got a spare. I'll ohm it out.and clean it before I install it.