1981 19" RCA XL-100 CTC108C no brightness after CRT cleaning - Videokarma.org TV - Video

joe111671 · #1 02-08-2020, 05:21 PM

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!

Popester · #2 02-08-2020, 08:09 PM

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

old_tv_nut · #3 02-08-2020, 08:11 PM

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

damen · #4 02-08-2020, 11:39 PM

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

zeno · #5 02-09-2020, 08:36 AM

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

LFOD !

Quote:

Originally Posted by damen

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

joe111671 · #6 02-09-2020, 02:16 PM

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.

Popester · #7 02-09-2020, 05:18 PM

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.

rcaman · #8 02-09-2020, 07:15 PM

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

joe111671 · #9 02-09-2020, 07:47 PM

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.

damen · #10 02-09-2020, 09:34 PM

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.

joe111671 · #11 02-11-2020, 05:03 PM

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.

zeno · #12 02-11-2020, 06:44 PM

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

LFOD !

joe111671 · #13 02-12-2020, 05:53 PM

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.

JohnCT · #14 02-12-2020, 08:16 PM

Quote:

Originally Posted by joe111671

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.

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

DavGoodlin · #15 02-12-2020, 08:25 PM

Quote:

Originally Posted by rcaman

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

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.