Just got a KCS-96 chassis set

[Aperna1985]

Hi guys uship just dropped off my new RCA TV. I don't know the actual model. There's an interesting story behind this set.apparently the previous owners dad was taking a tv repair course by mail and he believes this was going to be the guinea pig. He was cleaning out the house and found it in the Attic. Along with an 8 mm projector and all the books for the course. Once he finds them he's going to send them to me. Anyway I carried the set down into my basement it's shockingly heavy, and opened it up just to see what was going on. I heard a lot of rattling so I was concerned. The first thing I noticed when I opened it was a brightener so I was pretty upset, then I noticed he stole every tube out of the set but wrote down where each tube goes. I hooked up my picture tube tester just to see and the tube tests extremely strong with great cutoff. Has anyone seen a set with a good tube and a brightener installed? Anyway, I wanted to give reforming the caps a shot just to see if I could get any action out of the set. I used a 25w appliance bulb on my dim bulb and without any tubes it lights at about 50% brightness. Then I plugged in my solid state 5U4 and it went to full brightness for a second then dropped right down to the brightness before the 5U4 was installed. I see that at some point the main filters were replaced. I just don't know when. Is it possible they aren't shorted? I know I'll be recapping the set, but I'd like to put tubes in and see how it works.

[zeno]

First with the 5U4 out there is no voltage to the filter caps. Do the
dim bulb again with it in.
If it is a series string pull any tube out & run that test. If a // string
pull the hoz output tube. If things look good put the tube back in &
see if you get a raster in < 1 mn. If not the trouble shooting starts !
IIRC this is a "doughnut" chassis. They are a bitch to work on so take it very slow ! The idea is get the power supply up then the HV for a raster.
At that point you can judge how far to go.
The filter caps will probably work but need changing eventually, For now dont
spend the $$.

73 Zeno
LFOD !

[Electronic M]

Anybody could walk in to a store and buy a brightener. I've seen them on good tubes more than once...Most interesting case was a 1968 Zenith color. The set was low hour and the CRT was STRONG, but the 25KV from the flyback was more like 11KV...It worked surprisingly OK like that...The root cause was the original H output being weak... possibly the HV rect too.

It's not uncommon to see sets stripped of tubes. Home repair attempts usually involved bagging them and bringing them to a drugstore tube tester, if they were fine they might not go back in since the problem isn't a bad tube and that's too much work....
Also repair shops when they condemn a set will offen strip the tubes, then knobs and similar common trim, then toss the cabinet and rob bits off the cabinet....In some cases those steps didn't all happen at once.

[Aperna1985]

I finally got all the tubes and fired the set up. The cap for the audio section is bad it hums like crazy so I just pulled the audio output tube for now. This is all I get on the screen. I did substitute one of the tubes in the tuner so I thought maybe that was the issue. So I took my pattern generator and hooked it up to the grid of the video output tube, and couldn't pass a signal through. I tried a few different tubes nothing made a difference. I'm just curious where I should look next I figure I could try to learn something from this before I just blindly recap it. If nobody has the schematics I could take some pictures of the Sam's I have. I didn't get the digital I bought a folder set off of eBay.

[damen]

If you can't get anything from the grid of the 6AQ5 video output tube, start taking voltage readings there. Check for open contrast control, peaking coil off of pin 5 the plate, should have 190 volts on it, screen, pin 6, 255 volts. Does the brightness control work?

[Aperna1985]

Originally Posted by damen

If you can't get anything from the grid of the 6AQ5 video output tube, start taking voltage readings there. Check for open contrast control, peaking coil off of pin 5 the plate, should have 190 volts on it, screen, pin 6, 255 volts. Does the brightness control work?

The brightness and contrast controls work. What's interesting is the black bars spread a little as I adjust contrast. The horizontal hold doesn't do very much. I haven't been deep in the set but I'm wondering if it's a coil. I turned it about 4 complete circles before anything happened. Also there is a little ringing from the yoke.

Also I checked the 255 volts source and tube heater voltages on other tubes but I did not check there. I will check and report back.

[Aperna1985]

OK I had a chance to check the 6AQ5 video output tube. The first value is the Sam's voltage the second is mine.

Pin Sam's Volt My Volt

1 0 1.6 VAC
2 18 33 VAC
3 Ground Ground
4 6.3 6.3 VAC
5 190 139 VDC
6 255 227 VDC
7 0? 1.5 VAC

I believe the Sam's says 1 & 7 are both 0V it shows this as 1-7.

So what I'm seeing is my voltages are low on 5&6 would this be low enough not to be able to pass a signal? I tried sending a signal in on Pin 1 and on Pin 7. But saw no reaction at all on the screen.

Also how come I didn't see a negative voltage listed to turn the tube on?

I cant find my larger tube test socket to test the 6AW8 video amp. But am I right in thinking if I sent a signal through on the grid of the video output tube I should get some kind of a picture from my signal generator?

[Aperna1985]

I just decided to do the resistance readings on the tube socket. 1-4 were just about perfect
5 was 4.32k Sams says 3.6k
6 was 37 ohm Sams says 38
7 was 0 Sams says 470k

I can't find where pin 7 goes on the schematic. Also I'm wondering if C2 Section C is dragging down the voltage on pins 5&6.

[damen]

Have you tried swapping the 6AQ5 video output tube with one of the other 2 6AQ5s in the set? I don't think your voltage or resistance measurements are so far off as to cause this problem. The chassis uses an "extra" video amp stage, that why the video is fed into the grid of the CRT instead of the more common cathode connection. Is your video source signal negative or positive? Pins 1 and 7 are tied together inside the tube, usually only one socket connection is used. If you check voltage or resistance with the tube out of the socket you'll probably get very different readings on them.

[Aperna1985]

I actually took all the readings with the tube out. And I did try swapping all 3 tubes l, but it made no change. I never checked if the video source is negative or positive it's an old Heath kit signal generator. It actually has two terminals on it I assume the red is positive which is what I was putting on the grid, and I was putting the black to the chassis

[zeno]

Find another RF source like a game, VCR etc.
Kinda looks like a wide open filter cap. If it is you should get 2 bars rolling
through the pix.
Could be H hold. Some have a pot & a coil. As you adjust it the lines will get closer or further apart if thats it.
TIPS
The filter caps will almost always open & often have mung leaking out. Quick
test is just hang a 50mfd to 100mfd , 450 V in // & see if any problem goes away. Saves time & $$.
If H hold uses a pot for H hold center it then adj the coil.
Little coils in the video can just be jumped out. If its open the set will get
a pix again but it wont look right. Another time saver.

73 Zeno
LFOD !

[Aperna1985]

Originally Posted by zeno

Find another RF source like a game, VCR etc.
Kinda looks like a wide open filter cap. If it is you should get 2 bars rolling
through the pix.
Could be H hold. Some have a pot & a coil. As you adjust it the lines will get closer or further apart if thats it.
TIPS
The filter caps will almost always open & often have mung leaking out. Quick
test is just hang a 50mfd to 100mfd , 450 V in // & see if any problem goes away. Saves time & $$.
If H hold uses a pot for H hold center it then adj the coil.
Little coils in the video can just be jumped out. If its open the set will get
a pix again but it wont look right. Another time saver.

73 Zeno
LFOD !

Ok so maybe I will pick up 2 adaptacaps and just change the filters first. I was tempted to unsolder each lead and use my Heathkit C3 to check for leakage. It just bums me out because I was hoping to learn the symptoms of the failures.

[zeno]

If you are just starting get an old book that shows block diagrams.
It will describe each block, function & symptoms. Thats how I started
many moons ago. Maybe someone can recomend a few.

At this point the filter caps are good to change. You know you have a brite CRT, HV, so yoke, CRT, & flyback are good.

73 Zeno
LFOD !

[Aperna1985]

Ok so I replaced capacitor C1, the shame of it is the whole thing tested good except the audio filters. I also changed capacitor C62. When i tested it for leakage it tested good then slowly started to leak. I did replace it with one of the yellow plastic ones bevause it was all I had. Cap c62 goes between pin 5 of the video output tube and pin 2 of the picture tube. While it was out I ohmed out coil L50 and it measured 8.5 ohms instead of 7 so I think it's fine. We'll after starting the set up, I now have no picture. There is only 50v coming out of pin 5 of the video Amp instead of 190, pin 11 on the picture tube is showing 1.8v and pin 10 is about 360. I hear the high voltage running. So I'm going to take another Crack at it tomorrow maybe one of the new caps is no good. I tested them all for leakage before install but who knows.

[Aperna1985]

Here is a link to the Sams on my Google drive
https://drive.google.com/file/d/1fKn...w?usp=drivesdk