Newbie's First Questions RCA TS 721 Restoration

[Chris K]

I'm back my new friends. Picking up where I left off. I have sound now but I've lost the HV. Crap! Not sure what I did in rearranging some wiring on the electrolytic caps but there's no HV. I guess I'll have to start by opening the cage once more and check the flyback for continuity then go from there. The HV circuit is the simplest and first area the power hits so I'm not sure how what I did to get audio caused this. Pin 8 on the damper and socket 10 on the CRT feed are supposed to be about 340V DC and I'm getting about 100V less than that.

[old_coot88]

Originally Posted by Chris K

Pin 8 on the damper and socket 10 on the CRT FEED...

Chris, a suggestion. Er, more like a recommendation. When calling out 'pins', put in parentheses which element a pin goes to. Like, cathode, plate, G1, G2, filament. It'd be a huge help to the reader.

For instance, pin 8 of the 5V4 damper is cathode. Pin 10 on the CRT is Grid 2 (or just G2).

Actually, I prefer calling out the element first, with the pin number (in parentheses of course) left optional.

[Chris K]

Will do...actually, I have both HV and sound now but, again, no picture. Oy veh! I tried playing again with the ion trap but to no avail. Maybe I should walk from this one for now???

[Notimetolooz]

How do you know that there is HV?
Once you have something like the ion trap adjusted it isn't useful to go back and mess with it without a logical reason.
If the HV is OK and the set had raster before then something like the voltages on the CRT socket have changed. Check them.

[Chris K]

Originally Posted by Notimetolooz

How do you know that there is HV?
Once you have something like the ion trap adjusted it isn't useful to go back and mess with it without a logical reason.
If the HV is OK and the set had raster before then something like the voltages on the CRT socket have changed. Check them.

I checked the anode with a HV probe...5 KV which is what I had before when I had a picture. I can't keep the ion trap on because this CRT is not attached to the chassis and it needs to be removed whenever I want to turn the chassis on its side to do work or analysis underneath although I did mark position and orientation on the trap and CRT neck with a Sharpie. I had a pattern from a signal generator before. I'll check the CRT voltages. Thanks!

[Notimetolooz]

You might want to download a book here. "How to Troubleshoot a TV Receiver" by Johnson. It is too big for me to make into an attachment.
https://worldradiohistory.com/BOOKSH...helf_RIder.htm

Look about half way down the page and on the right for a book with a blue cover. It has some good pictures and explanations of problems. It probably doesn't help that much at the moment but it may in the future. Published in 1953, so for a much later set it may not be accurate.

[Chris K]

Originally Posted by Notimetolooz

You might want to download a book here. "How to Troubleshoot a TV Receiver" by Johnson. It is too big for me to make into an attachment.
https://worldradiohistory.com/BOOKSH...helf_RIder.htm

Look about half way down the page and on the right for a book with a blue cover. It has some good pictures and explanations of problems. It probably doesn't help that much at the moment but it may in the future. Published in 1953, so for a much later set it may not be accurate.

Oh thank you so much! yes, I need learned instruction and guidance!

[Chris K]

Originally Posted by Notimetolooz

You might want to download a book here. "How to Troubleshoot a TV Receiver" by Johnson. It is too big for me to make into an attachment.
https://worldradiohistory.com/BOOKSH...helf_RIder.htm

Look about half way down the page and on the right for a book with a blue cover. It has some good pictures and explanations of problems. It probably doesn't help that much at the moment but it may in the future. Published in 1953, so for a much later set it may not be accurate.

What a treasure trove! Thank you! I've downloaded several of these online books. Amazing basic information and believe me, I need it!

[Chris K]

So here is a question that puts my inexperience on full display. The electrolytic caps C131, C132, C116, C127 and C128 are not grounded to the chassis. When I have substituted for them, I've just tied all of the negative leads of the new caps to one another on a terminal strip. For example, the original C131 has a 30uf and a 10uf cap. I disconnected the leads to C131, put in a terminal strip, tied the negative leads of replacement 47 and 10uf caps together and re-soldered the chassis wiring back to the new caps. I didn't pay attention to replicating the negative lead specificity from the connections to the old cap because placing a meter lead on any of the 4 negative leads exiting the bottom of the original gave me the same capacitance reading on the 30uf and 10uf caps in the original. Would this be the correct thing to do, just tying the replacement capacitor negative leads and soldering the chassis leads that had in the original configuration gone to 2 negative leads on C131 to the single new tied negative? I'm not sure if my connections to the negative leads of the new electrolytic caps is causing new problems. TIA for any assistance.

Chris

[Kevin Kuehn]

Originally Posted by Chris K

So here is a question that puts my inexperience on full display. The electrolytic caps C131, C132, C116, C127 and C128 are not grounded to the chassis. When I have substituted for them, I've just tied all of the negative leads of the new caps to one another on a terminal strip. For example, the original C131 has a 30uf and a 10uf cap. I disconnected the leads to C131, put in a terminal strip, tied the negative leads of replacement 47 and 10uf caps together and re-soldered the chassis wiring back to the new caps. I didn't pay attention to replicating the negative lead specificity from the connections to the old cap because placing a meter lead on any of the 4 negative leads exiting the bottom of the original gave me the same capacitance reading on the 30uf and 10uf caps in the original. Would this be the correct thing to do, just tying the replacement capacitor negative leads and soldering the chassis leads that had in the original configuration gone to 2 negative leads on C131 to the single new tied negative? I'm not sure if my connections to the negative leads of the new electrolytic caps is causing new problems. TIA for any assistance.

Chris

Per Riders schematic C128B,C131A,C127A, C128A have their common negative leads going to the center tap of the power transformer(which is how the negative supply voltages are developed because the center tap is not tied directly to ground, instead negative voltage is formed across resistance to ground). However the negative lead of C116B actually goes directly to chassis ground. C132 also does not share a common negative with the other caps.

[Notimetolooz]

Originally Posted by Chris K

So here is a question that puts my inexperience on full display. The electrolytic caps C131, C132, C116, C127 and C128 are not grounded to the chassis. When I have substituted for them, I've just tied all of the negative leads of the new caps to one another on a terminal strip. For example, the original C131 has a 30uf and a 10uf cap. I disconnected the leads to C131, put in a terminal strip, tied the negative leads of replacement 47 and 10uf caps together and re-soldered the chassis wiring back to the new caps. I didn't pay attention to replicating the negative lead specificity from the connections to the old cap because placing a meter lead on any of the 4 negative leads exiting the bottom of the original gave me the same capacitance reading on the 30uf and 10uf caps in the original. Would this be the correct thing to do, just tying the replacement capacitor negative leads and soldering the chassis leads that had in the original configuration gone to 2 negative leads on C131 to the single new tied negative? I'm not sure if my connections to the negative leads of the new electrolytic caps is causing new problems. TIA for any assistance.

Chris

It took me a while to understand your question. The confusion came from you using the phrase "negative leads", I think what you are referring to is the four negative tabs of the original cap. Those tabs (for mounting usually) are mechanical structures that are all electrically equivalent. So sure, tying the negative leads of the the two new replacement caps together and connecting all the wires that went to the four tabs to that negative is correct.
What Kevin and I was afraid of at first was that you were referring to was connecting the negatives of all the different original caps together where they should be separate. That would be bad.

[Kevin Kuehn]

Originally Posted by Notimetolooz

What Kevin and I was afraid of at first was that you were referring to was connecting the negatives of all the different original caps together where they should be separate. That would be bad.

With the exception that the negative side of C116A,B,C,D does go to chassis ground. You really can't make any assumptions which requires learning to reference and decipher the schematic drawing.

Originally Posted by Chris K

So here is a question that puts my inexperience on full display. The electrolytic caps C131, C132, C116, C127 and C128 are not grounded to the chassis.

Chris

[Chris K]

Yes thank you both...you understood my very meandering description!

[Chris K]

Originally Posted by Kevin Kuehn

Per Riders schematic C128B,C131A,C127A, C128A have their common negative leads going to the center tap of the power transformer(which is how the negative supply voltages are developed because the center tap is not tied directly to ground, instead negative voltage is formed across resistance to ground). However the negative lead of C116B actually goes directly to chassis ground. C132 also does not share a common negative with the other caps.

C116B negative lead goes to ground? I'm not seeing that. It's not tied to the -85V center tap as well?

[Kevin Kuehn]

Originally Posted by Chris K

C116B negative lead goes to ground? I'm not seeing that. It's not tied to the -85V center tap as well?

I'm so sorry I was referencing my 621 schematic. I'll have to go look for the 721.