1981 19" RCA XL-100 CTC108C no brightness after CRT cleaning
 

I was at an estate sale where they had a bunch of CRT sets for free, they were all black or silver plastic except this one, so I grabbed it. It had a greenish tint to the picture and the reds were smearing/flaring like a worn out tube so I thought it would be good practice using my crt tester/rejuvenator.

The green pegged the meter, the red was less than half and the blue was in the middle. I used the "cleaning" function of the tester on the red & blue guns and that brought their emissions up to where the green was. I set the gray scale and it made a great picture & the red flaring was gone. It ran like that for a several minutes, then I heard a snap like something arced, I looked at the back and barely caught another arc out of the corner of my eye on the crt neck board, but I don't know exactly where.

Now the picture is gone. It does have a dim raster. The color, tint and contrast all have an effect but not the brightness. I'm wondering if I created a short in the crt that caused the arc on the neck board and blew a component. The crt still tests strong. Any ideas are appreciated!

Looks like video circuitry issue. CRT appears to be okay. Maybe a heater to cathode short. Others will chime in.

I think for one control not to work while the others do, the problem has to be in the circuitry, not the CRT.

Arcing in the CRT may have damaged a video transistor. Check Q703 located on the main board behind the service switch. It's an NTE159

Ditto
Sometimes a rejuved CRT, even a new one will arc at first. Also it looks
like jail bars in the pix. If there is when its fixed its an easy cure.
If it were a H-K short the pix would turn very bright for that color & sometimes
put the set in shutdown.

73 Zeno:smoke:
LFOD !

Back in business!
 

Thanks everyone! Damen you nailed it. Q703 was shorted across emitter & collector. The number on the transistor is 3474, and I have a CTC169 chassis in my junk box that had a couple of them, so I didn't even have to get the NTE159.

The picture has a green tint again, so I'm going to let it run for a few hours, and if it doesn't arc again & the crt holds up, I'll set the gray scale again and try to take a good picture. I'm hoping the tube stabilizes after it runs awhile.

Zeno - I don't see jail bars in the picture so I think it's the camera doing it.

That rejuvenated tube looks pretty good. Mr Howell and Ginger from some Gilligans Island show. RCA XL100 i thought always had a nice picture on them.

i sold a lot of those back in the day really good performing tv.

These are good performers for sure! I let it run for several hours, set the gray scale a couple hours ago and the picture looks perfect to me. I turned it off to take a picture of it, and a few minutes after I turned it back on, it slowly got really bright and had retrace lines. No distinct color, it was like I was cranking the screen control. I turned it off & back on and it's been good for an hour now. Not sure what that was about but I won't be surprised to see it again.

The cabinet cleaned up really nice. Not sure why the pictures got rotated.

Issues you're having were very common after some tubes got rejuvenated. I always imagined little pieces of "crud" that got blasted off the cathode during the process were floating around in the neck and sometimes settled between the gun elements resulting in the arcing and flashing. After awhile things will settle down. As far as the bright picture, if it continues to act up try shorting pin 5 of the CRT socket to ground. There is a 100K resistor (R14), and a cap (C2) in parallel to ground from pin 5, just solder a jumper across the cap. This will darken the picture slightly, but you can turn the screen up to compensate for it. This will keep the picture from going bright when a piece of crud lands between the screen and grid elements of the gun.

That makes sense & good to know it's common for those issues to happen. I ran it for hours over the last couple days and it seems fine now. Man this thing can make a good picture. It's going to replace the 1975 Sears Sanyo 19" I've been using for the Nintendo. It works fine but just doesn't have the clarity this one does.

Zeno, I can see the jail bars if I pause the DVR on a dark screen between commercials, so it wasn't my camera. I'm not worried about it but just curious what the fix would be, if it's an easy fix I'll do it just for experience sake. It doesn't have that blue tint in person, it's the camera this time.

OK remember this one. Its common to all brands.
The 3 color outputs are supplied with apx 200V. There is an electrolytic
off it. Usually 4.7 or 10 mfd @350V. On your set IIRC there is a big can
along the front of the chassis. It has two sections. One abt 800mfd
the other is the one you want. Just cut the wire off the 10mfd section
& install a new one to the wire. The 800mfd stays in. RCA got about
$20 for the cap so thats how we did it.
Symptoms are any of following.
Jail bars
Retrace lines
Pix dark at left & gets brighter to the right
Too bright
Streaking / bad CRT look
Pix is just not right

73 Zeno:smoke:
LFOD !

Thanks Zeno. The big can on this set only has one section. I looked around for either a 4.7 or 10 mfd @350v on the board but things are pretty tight in there and I can't see the values of many of the caps so not sure which one it is.

That is the cap that caused the issue on my 1975 Sears! It was so bad that the set was almost unwatchable. I actually found the fix for that one on the sci.electronics.faq website, but on the Sears it was pretty easy to locate the cap. This RCA not so easy. I could find it with a schematic, but I searched & couldn't find one out there. Anyway, thanks for that list of symptoms - I had the impression that cap being bad would only cause the dark on the left, bright on the right.

Some had the dual section, some didn't.

IIRC, the cap in question is about the 10 o'clock position at the flyback looking from the back, but it's been many years since I did one.

In any case, you can bypass the line right at the CRT socket. Add a 10uf/350 right on kine source line to ground.

John

I unboxed, set up and delivered many a set like that too. It was not unusual to see the CTC101(?) 13" thru 19" XL and Colortraks from about 2 years earlier come in at the same time for the "factory flyback kit" special. I think they sent us parts at cost to do the repairs as the sets exceeded 1 year usually.

We wondered if the new ones would keep us busy 2 years later but I dont think they did. :scratch2:

Yeah, it was a short run of flybacks in the 1981 model year. I was surprised when I got a call from a customer with a ColorTrak 2000 I had sold him that went dead. I thought it was a nuisance call but was surprised to find the horiz output shorted. Put in a new one and blam. I figured the retrace cap must have been open (like those GEs did), but the cap was good. Stunned to find a bad flyback.

The incidence of any RCA needing a flyback after they went to the Trans Vista and XL100 solid state TVs from the early 70s on was virtually nonexistent.

According to our field rep, it had something to do with a bad batch of epoxy used to encapsulate the transformer.

John

I was determined to find this cap so I spent a little time finding the values on every electrolytic around the flyback. Picture 1 from left to right are 820@25v, 68@35v, 820@25v. Picture 2 330@35v, 30@250v. None of them are what I'm looking for except maybe the 30@250v but I don't want to assume anything.

John, not sure what you mean by kine source line, but my best guess is 13B which looks like it feeds R10,11,12 into Q1,2,3. I attached a picture of the back of the neck board. If you know off the top of your head where I would add the cap, I'll give it a shot. Otherwise no big deal, the picture is great as is, the bars only show up on a dark screen so I'm ok with just leaving it alone. I appreciate the input from everyone!

Where R1, R2 & R3 join follow that back to the main PCB. It may go through L1
first. The cap will be on that line. It will be on the cathode of a diode.
If you have a schematic of almost any solid state set the circuit will be
all but the same.

73 Zeno:smoke:
LFOD !

Will do. Thanks Zeno.

The only schematics I have are for my tube sets and a solid state Portacolor II but that schematic is pasted inside the back cover. I'll open it up & get a picture of it. Won't hurt to have a good picture of that as I want to see if it can be resurrected someday.

Well this is turning out to be difficult to find the cap.

Zeno, when you said follow where R1, 2 & 3 join - I am assuming you were referring to R10, 11 & 12 that go to Q1, 2 & 3. So if my assumption is correct (and if it's not, then I'm way off and please correct me), the resistors are fed by wire 13B, which on the main PCB goes to 13A. 13A connects to multiple traces on the PCB that lead to various resistors, one of which leads to the video transistor that I had to replace. Trying to make a mental schematic of all that is beyond me, but I can't see where any of it is connected to the cap I'm looking for.

And the only solid state schematic I have is for that porta color (JA chassis), but on that one, the RGB transistors look to be fed off the power supply instead of the flyback, so that is no help for me with this set. That is my dilemma. Not the end of the world though, I just wanted to change the cap and see if the bars went away.

If anyone can see that I'm missing something obvious and you want to smack me, feel free to point it out. :rockon:

The Sams shows that 30 at 250 volt cap to be C117. From pin 9 of the flyback there is a diode CR112 with a small cap across it C116 that connects to a 4.7 ohm resistor R125, the resistor is probably raised above the printed board on 2 metal "stakes", then C117 is connected to the resistor and the wire run up to the CRT socket board. It then connects to the junction of R8 and R13 shown at the top of the picture you posted. Looks like it might say "9B" with L1 under it.( Sometimes the board call out numbers may be abbreviated. Example, C117 may just show C7, or CR112 may just be CR12)

Found it, thanks Damen. R1, 2 & 3 were right there but somehow I completely missed them till I followed the circuit from the flyback up. Zeno you were also right on, sorry I missed what you were trying to explain to me, I only saw R10, 11, 12 at first. :sigh:

I don't have that cap so will need to order it.

In the meantime, the set has developed another issue. If I turn the brightness down to around half, the video just cuts out. It comes back abruptly if I turn the brightness almost all the way back up, then it can be lowered again, but if I turn the set off at the lower brightness level, there's no video next time I turn it on till I crank the brightness. I'm going to guess it's Q703 again since it is what killed the video the first time, and I installed a used one that I grabbed from a junk board, so maybe I damaged it with all the heat. If it loses video altogether, I will check that one first.

I think I'm done with this set! Q703 shorted again, causing the video to cut out like it did. I don't know why it happened, but rather than install the other used one that I harvested from the junk chassis, I checked with the electronic supply store in my city & they had the NTE159. They also had a 33mfd @ 250v so I grabbed that to replace the 30mfd@ 250v. They even had the SAMS for this set for $10 so I got that as well.

Video problem is fixed, bars in the picture are still there so that cap wasn't it, but they're really not noticeable enough to pursue it further IMO. It was cool finding this set and interesting working on it, and I hope it keeps working like it does.

For anyone interested, Chester Electronics is in Kenosha, WI. Someone did a Youtube video recently in the store, if you want to check this place out, it's amazing. They even carry vacuum tubes and have a tube tester.

https://www.youtube.com/watch?v=VAs7adDdcaQ

Thanks to everyone who chimed in here.

I go to Chester electronics occasionally.

There is one thing they sell that I no longer buy: Electrolytic Capacitors. Most of their stock has been sitting longer than I have been alive. Lytics go bad from age and they fail faster when they spend significant periods of time without voltage on them. The first time I went to Chesters I bought some lytics and tested them for esr and leakage. Atleast half were marginal or bad. There's a fair chance the caps you swapped in are as bad or worse than what you pulled out.

You would be better served going with an online supplier with fast turnover like mouser, digikey, Newark etc. and spacing out a good brand 105c rated cap. IIRC Chester also is more expensive than them.

The stuff to go to Chester for is NTE semiconductors that have been out of production so long you can't find them online and stuff for 50s-70s sets that you can't believe NOS parts still exist for.

You have a good point, I didn't think about that with the electrolytics, but it makes sense. They keep everything on the shelf till it sells, which is great, but not so great for items with a shelf life.

Potential CRT donor found
 

I found another RCA at an estate sale, this one is a 1984 with a CTC118 chassis. I powered it up, there was no signal to it but the snow appeared crisp with no dominant color, so I grabbed it. It was interesting to find this shortly after the 1981, because I never see 19" RCAs from the 80's and I've been going to estate sales for years.

It has cigarette burns on top, plus it stinks like cigarette residue, so it's not a keeper. But it makes a great picture, the crt tests great, and looking at the two RCAs side by side, I can see that this crt has better focus.

I want to take the tube out of the cigarette set and put it in the keeper, since that one is only good because of the zap from the rejuvenator, and my understanding is that restoring a crt may only be a temporary fix.

The yokes have different plugs which I can work out. The SAMS for the CTC108C shows yoke resistance to be 10 ohms on the vertical and 1.4 on the horiz. I measured it and that's what I got.

I don't have a schematic for the CTC118. The vertical on that does measure 10 ohms, but the horiz has a cap in series with it so I can't measure it easily. I don't know the significance of that cap so I hesitate to do the swap & I don't want to disturb the convergence tape by trying to swap yokes.
I really want to try this but don't want to ruin a good chassis or yoke.

Any advice is appreciated!

If it helps:
CTC108C=19VLNP22
CTC118=A48ABE10X

It's not just resistance of the windings, but also the inductance of the yoke windings that must be taken into consideration for a swap.

I think I have the setups for both these chassis for an RCA test jig (or you may be able to find this on line).

If the setup for the two chassis is the same, it would be safe to try. A lot of times the setups for different chassis might have too much width on one, less on another, vertical shrink etc. But if the switch settings are the same, it will work without creating an annoying mushroom cloud on your bench. Any slight differences between the yokes could likely be fudged at the chassis by changing some values.

I'll check tomorrow at work. If you don't hear from me, ping me..

John

Will do, thanks John.

The CTC118
 

This is the set, it's probably a good thing it looks & smells like an ashtray. Makes it easy to decide which one I'm keeping.

Sams shows the specifications of the two yokes to be very close. That cap on the yoke of the CTC118 set is already on the circuit board of the CTC108, just by-pass it, or wire in the yoke wires from the 108 yoke.

If you have an issue with the vertical size,meaning, can't fill the screen with the size control, or, the picture is too tall and can't be pulled in, it may be necessary to replace the resistor for the vertical return circuit from the yoke. It's R522,a 1.8 ohm 2 watt in your 108 chassis, and R518, a 1 ohm resistor in the 118. Just swap them.

Successful transplant
 

I changed the yoke wiring right at the yoke, cleaned up the donor crt and installed it. The vertical was not filled out all the way, which wasn't unexpected based on Damen's point about the resistor values. There were retrace lines & the picture looked green deficient. No strange sounds or smells though. The focus looked good but I adjusted it anyway.

I setup the gray scale according to the Sams instructions and it came out nice. The height control filled it all the way out with some room to spare. The wiring came out good so I'm calling this a success.

Next I want to put the ashtray set back together and see what that does. I'm curious if everything is the opposite of how this looked at first.

Once again thanks for the advice guys.

Maybe you could have swapped the chassis of the ash tray set into the older set cabinet. To be reunited with the CRT from the ash tray set. That would take care of the vertical height issue. The tuners might be an issue, but they all have a standard IF frequency. Only issue might be supply voltages, but you probably can create workarounds for that. But it sounds like you made the ashtray CRT work with teh CTC108 chassis.


I worked for RCA Sarnoff Labs back then. The flyback transformers used six windings, and 3 diodes to create the very high voltage for the CRT. They thought they could get away with just the 3 diodes, cheaper. Wrong! The terminations of the windings and diodes were a stake style, which created electrostatic stress points. Had they used 6 diodes, one diode per winding (winding-diode-winding-diode-winding-diode-winding-diode-winding-diode-winding-diode) these stresses would have been half as intense, and the flyback transformer would not have failed. When they made the 6 diode flyback, they used a different color epoxy than what they used in the 3 diode flybacks.

I had a CTC101 and loved the picture it made. It had the line comb filter, for better chroma-luma separation (something I did a lot of work and patents on at the RCA Labs). Unfortunately, that CTC101 did have the bad flyback, but it lasted about 10 years before shorting out...

The diodes would certainly explain it. I do know that a lot of them failed in warranty and that RCA fixed it immediately. Once they did, I cannot recall any integrated flybacks failing until the 177 and 195, and even those were rare.

I did warranty work for RCA in the 80s, and until the 140 went into production in the late 80s (1987?), we had gone many years without making a single claim to RCA for warranty work. When the 140 came out, we had a couple of issues with them (GREAT performer) and we had to call RCA to get the procedure to submit claims.

John

Done
 

The swap looks like a double success, they are both now running with each other's crt & yokes. There was just the gray scale setup and that vertical height issue, one needed to be increased & the other reduced, and now they're good. The rejuvenated crt definitely doesn't have the focus of the one out of the CTC118 so I'm glad I took the chance. It's hard to explain but it's like there are halos around bright text, and the focus control gets rid of that, but at the expense of taking everything else out of focus.

I almost tried that, but decided to see if the crt swap would work. I actually felt more intimidated by trying to get the tuners swapped, but it worked out and was good experience. I'll keep the chassis out of it just in case, unless someone wants the whole set.

Vert centering issue
 

The vert size on the CTC108 filled out by adjusting the control, but I noticed that it's not centered, it's down too far. I can't find any way to center it by looking through the Sams. Do you think swapping these resistors will have an effect on the centering? Or is there some provision for adjusting it that I can't find?

I don't know if that resistor would affect centering or not. You could parallel the 1.8 ohm resistor with another 2 ohm resistor temporarily under the board to see if bringing the value down to 1 ohm helps or not.