Another KCS47 Restore...No High Voltage/B+ Down 25V

[bandersen]

Yep, tube needs to be in the socket to develop that grid leakage bias voltage Tom mentioned.

[Kevin Kuehn]

Originally Posted by bandersen

Yep, tube needs to be in the socket to develop that grid leakage bias voltage Tom mentioned.

Of course. I suggested he do that to verify if any B+ was leaking onto the grid from the horz osc section. Apparently not.

[Kevin Kuehn]

Originally Posted by Chris K

Pulled the 6BG6 and there's no voltage on the grid (5) and the plate (8) is 410V DC

At least now you know where some of your B+ is being lost to. I think once you've replaced the paper caps in the horizontal section your sawtooth will increase in amplitude and the 6BG6 will get it's proper grid leak bias.

[Chris K]

Ok gonna finish the horizontal and vertical recap tomorrow and I’ll see what happens.

[Penthode]

How many of the paper dielectric caps are still in the chassis? If you haven't replaced them, the B supply will be pulled down by the leaky caps upsetting the bias voltages.

Before powering and chassis of this vintage, you must replace the caps first.

[Kevin Kuehn]

Originally Posted by Chris K

I’d like to know for education purposes what’s causing this specifically and how I can diagnose issues like this in the future instead of doing a bulk recap in the power and deflection sections. I’d like to be able to say oh that’s what caused it and not well I changed everything and that took care of it.

Chris,

I have an idea that might be less painful than the way you're trying to go about this. Identify the circuit location on each of the old caps as you remove them. After you have the TV working with new caps, you can experiment with putting the old ones back, one at a time. Then you can evaluate how they influence the operation. It will be easier to do once you have a working base line. You could even keep a spare chassis on the bench just for experimentation. The more you measure voltages and look at waveforms on your scope the easier it will become to wrap you head around how the circuits interact with leaky or out of tolerance components.

[Chris K]

Before the first power up I did a dim bulb series to make it safe. When I got no high voltage I replaced the 3 electrolytic cans with 4 section adapt-a-caps and a few but not all the caps in the power, horizontal and vertical sections. It’s interesting there are so many opinions on this process. Bob has commented here replacing all the caps is the prudent thing to do but I’ve watched restoration videos of his where he baselines an untouched chassis from this era using a gradual power up with his Sencore isolation transformer Variac. Shango usually does the same although his videos are more resurrections than restorations and he has no fear of the magic smoke. I don’t do a power slam at 120V without replacing the cans first because I have seen videos where a short can take out a transformer so I don’t want to risk that. Are you saying I should replace everything or just the cans and all waxies in the 3 main power sections I've been working on? Is leaving the RF and IF caps alone until I get HV and a full deflection raster an ok thing to do or am I still asking for trouble with a shorted cap in the video and sound signal sections? To be honest, I usually have done complete recaps prior to first power up but from what I’ve watched that’s not SOP. Gradually replace the paper and foil caps and check function often before proceeding is the smarter more conservative approach. That’s what I surmised anyway.

[Chris K]

Originally Posted by Kevin Kuehn

Chris,

I have an idea that might be less painful than the way you're trying to go about this. Identify the circuit location on each of the old caps as you remove them. After you have the TV working with new caps, you can experiment with putting the old ones back, one at a time. Then you can evaluate how they influence the operation. It will be easier to do once you have a working base line. You could even keep a spare chassis on the bench just for experimentation. The more you measure voltages and look at waveforms on your scope the easier it will become to wrap you head around how the circuits interact with leaky or out of tolerance components.

Thank you for that suggestion! I actually finished the recap in the vertical and horizontal sections tonight but it was late, I got tired and I didn’t want to risk powering the tv up in that state. I did test some of the caps as I replaced them and one in particular had a very high ESR…somewhere around 75 ohms. In bed and I don’t have the schematic in front of me but it was a 102 paper cap rated at 1000V…C155 🤔 maybe. The rest of the wax caps tested fine accurate with
low ESR. The bumblebee caps were a different story and were all bad. Anyway we’ll see tomorrow if it works, is the same or smokes!

[Chris K]

Actually it was C156

[Kevin Kuehn]

Originally Posted by Chris K

Before the first power up I did a dim bulb series to make it safe. When I got no high voltage I replaced the 3 electrolytic cans with 4 section adapt-a-caps and a few but not all the caps in the power, horizontal and vertical sections. It’s interesting there are so many opinions on this process. Bob has commented here replacing all the caps is the prudent thing to do but I’ve watched restoration videos of his where he baselines an untouched chassis from this era using a gradual power up with his Sencore isolation transformer Variac. Shango usually does the same although his videos are more resurrections than restorations and he has no fear of the magic smoke. I don’t do a power slam at 120V without replacing the cans first because I have seen videos where a short can take out a transformer so I don’t want to risk that. Are you saying I should replace everything or just the cans and all waxies in the 3 main power sections I've been working on? Is leaving the RF and IF caps alone until I get HV and a full deflection raster an ok thing to do or am I still asking for trouble with a shorted cap in the video and sound signal sections? To be honest, I usually have done complete recaps prior to first power up but from what I’ve watched that’s not SOP. Gradually replace the paper and foil caps and check function often before proceeding is the smarter more conservative approach. That’s what I surmised anyway.

No you don't want to replace ceramic caps in the RF and IF unless you later identify a known issue with one. Keep in mind some of the individuals you watch videos of have a vast experience with how these circuits work and lots of doing under their belt. Shango in particular does things different just to go against the grain. Don't me wrong, he's a brilliant technician, but he's also intentionally adding drama for the sake of viewer engagement. I get his humor, so I'm not offended by any of it.

[Chris K]

Ok well, I’ve completed the work in the troublesome sections. Hopefully it will be closer to what it’s supposed to be when I power it up in the AM. The jammed up orientation of components under the HV cage is a real pain in these early RCA TVs. Not service friendly for sure.

[Kevin Kuehn]

ESR isn't very useful when it comes to testing paper or film caps. That's primarily useful for finding high resistance or open small electrolytics while they are still in circuit. Completely different than leakage. Although if C156 had high ESR it's probably bad just the same.

[Chris K]

I tried it today with every cap replaced in the sections we’ve been talking about and I got a raster on the 5” CRT. That’s the first time that’s happened. HV unfortunately hasn’t changed much, still hovering around 4K. I didn’t get a chance to do any voltage checks or look at any traces. I think there may be an issue with the yoke and how I have it mounted because it’s out 90 degrees. The horizontal changes with the vertical and vice versa. Doh!

[Kevin Kuehn]

Originally Posted by Chris K

. The horizontal changes with the vertical and vice versa. Doh!

Interesting. Is it just rotated 90 degrees? The horizontal and vertical are still acting on the correct axis of the picture, as in you didn't change the wiring on the yoke plug?

[Chris K]

I didn’t but I completely disassembled the yoke and the mounting when I fixed the stripped nut so maybe something got messed up. The back cardboard cover was ripped and destroyed so I 3-D printed another. I’ll have to look more closely at it. My recollection is the screw hole on the yoke for the rotation adjustment wasn’t removable but maybe it was and I remounted it 90 degrees out. I definitely did not change any wires on the yoke plug