Advice sought for 1968 RCA GL-644W
 

Hi, all,

First post to this fine, fine forum. Wondering if any could chime in on what happened to my recently-acquired RCA Vista Color, and maybe even suggest a fix. When I got it home and turned it on, it only lit up the screen--no usable sound or pictures (a low buzz at full volume). I found one of the tubes was incorrect, from the diagram (6GH8A had a 6U8A plugged in). I ordered all new tubes on ebay. When I replaced five of the 12, it was working pretty darn good on all fronts.
When I got to replacing the last two tubes (6GF7A and 12HG7A), the picture lit up so strong you would think it was new. I adjusted a few of the picture controls to maximize. However, after a couple days the pic started reverting back to only being lit up or a very dark, blurry picture, with no sound. I could temporarily fix this by wiggling/positioning the 12HG7 (the problem area I think), or lifting up one side of the set a couple inches and letting it drop back to the ground. (Yes, I'm a rocket scientist). Nonetheless, after turning it off and then on again later, it was almost always screwed up again. I did try putting the old 12HG7 back in, but no help.
I cleaned and re-soldered the connections of the 12HG7 tube "caddy" plug-in terminal. I can get the tube to light up continuously now, but no fix. I tried putting a different tube in as a last ditch for 30 sec., but no fix, of course. I ended up watching the CRT tube go from lit up to dark in 5 seconds, and that's were she stands. Had to give it up. Didn't hear anything that would indicate the CRT was damaged in any of my trials.

Any suggestions for this layman, packing a soldering gun and electronic component cleaner? (Try not to be cruel..!)

Thanks,
Carl
(Radiophile2001)
www.geocities.com/radiophile2001

hummmmm... what chassis is in your set. From 1968 I would assume a CTC-31 or a CTC38. It's got to be something in the 12HG7 (vid output tube) Did you check it on a tube tester. You may have a bad tube (new doesn't always mean they're good) Also make sure ALL the correct tubes are in the set. 6GH8's were always known to be a short-lived tube and they almost always test bad.

Did you check the solder connections between the circuit boards and the chassis? These are important ground connections and usually crack from thermal stress.

AGREED! The solder connections are #1 on those sets. That means every tube on all PC boards, and all of the places where the PC board is mounted on the metal tabs must also be resoldered. I would start with that, and also you could very sparingly spritz the tube pins with tuner cleaner and wiggle them to make good contact.

You didn't damage the picture tube, based on what you said.

Charles

I can't imagine the CRT getting damaged. What kills them is either a 'burn in' or if you REALLY push the voltages out of wack.

When you say 'dim and blurry', does it look like the TV's focus went out? If so, the 2AV2 (it's got one, right?) might be loose.

Pleae be careful in there, though. Voltage on the CRT is 25,000 or so, and the horizontal and vertical sections pack a good wack, too. Once the set's off and unplugged, it's not too bad, but the CRT can store up a bit of a charge that can startle you. Use common sense, especially around the sweep circuits and the HV suction cup on the CRT, and the HV section.

It sounds like you've got a few intermittent solder connections. Welcome to the wonderful land of RCA ;)

Thanks, all....

Will check the connections between the chassis and boards. Not sure what # the chassis is....will have to check. I'm assuming the tubes are good, because both the old one and new one don't seem to work. The old one did work before the new one was put in, just not as robust. Don't have a tester.

Could there have been permanent damage done by placing the wrong tube in place of the 12HG7 and turning on the set briefly?

Thanks

Hello! Glad you found us!

It would seem the most likely thing that could have been damaged was the wrong tube you tried. Do you know the type number? I guess you know that the '12' in that tube # refers to the filament voltage, so if you stuck a 6 volt tube in there you probably killed it. Other than that, if we knew what tube it was we could look up the specs on both tubes and compare them. I'd say chances are very good that no damage was done to the circuitry.

I had a CTC-31 that did some really goofy things thanks to solder joint problems. While troubleshooting it I subbed another video tube in there; the used replacement I tried was defective which unleashed some really bizarre intermittent behavior in the set.

Fixing those joints is not the easiest thing to do. To do it right you have to pull the chassis, a pain (but easier on this than some other models), and then you have to contend with the limited space they allowed.

I would also follow up on what nasadowsk suggested, the focus tube if it has one. It would also not surprise me if this was something like a horizontal output tube problem or some such. I am reminded of how my CTC-11 acted one day; it had been working fine and then the picture went small & fuzzy and then went away. I have a hard time now remembering just what the problem was; a bad electrolytic cap, I think. (there were a series of problems with that set)

Doesent the 12HG7 use a center-tapped filament to run at 6.3v?

I've found 6U8's in place of 6GH8's before. The 6GH8 is an improved version of the 6U8.

RCA wouldn't have 1-2 12v tubes running with 6.3v stuff anyway/..Not including such things as series string chassis... Dont you hate trying to find those odd tubes now? 13GF7, anyone?

There are zillions of weird filament voltages, mainly in cheap portable TVs from the early 70s. How about a 53HK7, or a 29KQ6, a 117JZ8 (only saw one in a cheap 9" Midland B&W with a solid state chassis except for that one tube), or a 19GH8? A couple of those are so goofy that they aren't even in the last RCA tube manual. I have a lot of those weird tubes, if anyone needs. But be patient, as I do NOT have them sorted. Just a 30-foot by 8-foot room full of boxes of tubes :sigh:

Charles

I can tell you this, that set has shocked me twice now while working on it.....beats coffee any day of the week! ;-)
(Yes, for the most part, I unplug it first.)
"Pulling the chassis" sounds pretty complicated. Is it just unscrewing the chassis from the wood of the set and disconnecting a few wires? That would be do-able.
Again, my first objective would be to check for solder breaks between the PC board and chassis. This can only be accomplished by pulling the chassis, no shortcuts? I have cut away some of the soft, vented particle board from the bottom of the set already to get in there and solder the 12HG7 tube plug. I turn the set over on its face using couch pillows to cushion it. A nice 500-watt halogen light makes seeing things quite easy.

Thanks

You would have to pull the tuner/controls module also. There are 2 screws in the chassis on either side of the power interlock to hold the tuner assembly in the service position. A magnetic nutdriver is a godsend when installing screws around the tuner. On most RCA's I've seen, simply loosen the tuner screws on the module after you remove the knobs, etc, from the front. Lift slightly and pull straight back and out. Be careful of the old wires, and dont twist or tangle them.

Unplug the speaker, yolk, convergence board, picture tube socket, and HV connection on the kine. You NEED to ground the HV connection with a length of wire around the shaft of a good screwdriver connected to the chassis. Stick the blade under the cup. Keep your hand away fron the shaft of the screwdriver, and use one hand ONLY! You will hear the snap when it grounds out. Disconnect the connector at the kine. Be careful around that kine connection. It can shock you even after you unplug the HV wire! Been there, done that.

Always remember to use ONE HAND when messing around inside the set. Put the other in your lap or something. Dont mess with the HV cage while the set is running!

If you feel uncomfortable doing this, remember to be very careful covering up the hole you enlarge under the set. I know of a cat that got shocked under a set where the cover was left off. No anti-cat comments, please. I have 3. They are evil, but I wouldn't hurt any of them.

If you are getting shocked that is not good! There is 400-1000 volts DC in there with a lot of current behind it, not to mention the HV, please be careful. I do not even probe live in these RCA's, I make an alligator clip connection to the meter with the set unplugged and then plug in to get the reading.

For discharging the HV I connect one end of a meter probe to the CRT degaussing shield ground connection (not on a painted part) with an alligator clip lead and stick the probe end up under the CRT anode cap till you get a spark. Remember you MUST discharge the CRT again before you re-connect the anode lead as the charge will reaccumulate. The degaussing shield connection gives you the best ground point as it connects to the CRT outer coating no matter if the chassis is connected.

Also when you reassemble you must make sure the CRT ground strap (usually running from the CRT shield to the chassis along the bottom of the cabinet) is firmly connected or you will get arcing or can get shocked from the CRT outer shell.

Thanks for the directions.....!

Here's a dose of reality: What is a kine? I know I fiddled with the kine knob when the set worked. This all seems a bit more than this quasi-layman is capable of. Thankfully, Bryan Gadow (who turned me on to AK) said it is within the realm of possibility he may fix it for me someday. I'm about 125 miles from his house. I had the priviledge of meeting him after winning his 1968 Zenith color set on ebay. I also went home with another set--his 1969 RCA Mural TV (color). We've seen them all in Holiday Inns decades ago. They both work great. I found the Zenith to greatly improve on UHF with a signal amplifier/antenna (Philips model bought at Wal-Mart). I also fiddled with the peak picture and contrast on the Zenith to make the UHF picture much better. Needless to say, I'm glad I don't have to mess with them, as they are in good working order.

PS. Question for anyone: I have a 1963 Curtis Mathes AM-FM tuner that came from a TV-phono console. It works quite well and has that great green electric tuning eye.
However, it intermittently has beefed up reception and then lower sensitivity (like you would turn a signal amp on and off with it). It's unreal--this can change back and forth by turning on a light in the room; the computer; and even changing from VHF to UHF on the Zenith.....very bizarre.....any idea how this is actually possible? i.e. The stations will come in kinda weak with minimal strength shown on the tuning eye. You change to UHF on the Zenith and all of a sudden the Curtis Mathes seems like you're just entered the 60 db contour. These are not even plugged into the same outlet in the room!

Anyway, just rambling here....need to educate myself better on that RCA GL-644W before fiddling with it more, I believe. ;-)

The first thing is to check for bad solder connections and intermittent tube socket connections. Try tapping various parts under the chassis with a plastic screwdriver handle. Next you can try swapping the RF and IF tubes one at a time. If replacing a particular tube doesn't fix it, put the original back so you don't chance the IF alignment too much.

I had a McIntosh MR-71 with similar symptoms. It was caused by poor connections to the mica caps in the bottoms of all the IF cans. It was a REAL pain to replace all these (required removing and disassembling all the IF cans followed by a full IF alignment).

Dang, and I've got that thing aligned and calibrated perfectly right now. So something as simple as turning on a box heater in the room can cause an intermittent tube socket connection to be altered....?

Seems like extra-dimensional to me....!
Thanks for the advice.

A KINE is short for Kinescope... another word for the PICTURE TUBE. It's pronounced almost like the name Kenny. a kenny-scope.

You may have a tube called a 6GU7 that is the G-Y / Blanker tube. Check its socket as the blanker can cause the screen to go white. Check your schematic on the HV cage. I may be wrong about the type, but look and see which tube is your blanker.

The 6GU7 will be used in the deluxe type RCA's such as a CTC-25 or CTC-30.
The cheaper models such as the CTC-31 or 38 will use I think a 6GH8 in this function.

The schematic will mention which tube is the blanker tube?
Yep, there are 6GH8s--5 of them. I have the back on it now and it's against a wall, but if I can determine which is the blanker tube, I will focus efforts there. Indeed, it went to a white screen, and then it went black finally.
I'm really trying to avoid pulling the chassis just yet. May be an easy fix here.

thanks

Update on the RCA:

* Re-soldered five of the connections between the chassis and PC circuits. They were broken connections before, from what I could see.
* Found that one of the two tubes I did not replace with new ones has gone out. That may explain why the CRT went black.
* This tube also should have been a 6CL3 from the diagram, but is a
"6CJ3/6DW4B/6CH3". Any advice on this? It was lighting up when I first got the set and when the set was working. I can't get it to light up...cleaned the tube plug and checked for breaks in the solder....Wiggled the tube a bit too. The tube has a shaking sound inside.
The blanker tube seems OK to me, but I have no tester. It's a new tube (NIB).
The Chassis is CTC38A.

Thanks!!

Investing in a tube tester would be a good thing :) Your damper tube shouldn't be making a rattle noise when you shake it. The type that is in there is fine. I think that's the "newer" type that RCA used and I'm surprised a CTC-38 didn't have that type in there from new. You have a good set, but they have the higest flyback failure rate of any RCA chassis I am familiar with.

Quick question:

What is a flyback failure and what are the symptoms of it happening? ;-)
So when I go to get a a new damper tube, which number would you recommend?

Thanks

Flyback failure occurs with an overload on the horizontal output circuit causing the flyback (horizontal output transformer) to burn out. I had a CTC-31 flyback meltdown, it started smoking and burned everything in the HV cage. I have been installing fuses in the horizontal output cathode circuit, 300 ma (1/3 amp) seems to do.
You will want to make sure the horizontal output current is not too high...for this I have removed the cathode fuse I installed and replaced it with a 6.3 volt lamp, then adjusted efficiency coil for minimum lamp brightness.

The weird thing is that the series filament portable RCA tube color sets had horiz output protection built in but the consoles do not. One type used a dual circuit breaker with two terminals for the power line and two for the horiz output cathode. Either a power supply overload or horizontal output overload tripped the breaker.
Another type used a thermal fuse in the HO cathode circuit. This sensed temperature near the HO tube and if the tube got too hot it would open the cathode circuit.

Chad (or anyone);

I never smelled anything burning or smoking on the set. But it seems when I put the last two tubes in (which included the 12HG7), it got pretty bright, like a new set. I also adjusted the back of chassis to maximize brightness, sharpness and picture quality. After that, it seems things started to go downhill.
However, I don't think the HO transformer was burnt out because for two days there before it died I was able to get it working again by either positioning the 12HG7 tube just right, or lifting up one side of the set and setting it back down "hard."
Is it possible that all of the adjusting I did and all the new tubes overloaded something?
Note the 6CL3, aka, "6CJ3/6DW4B/6CH3" died on me in the process. Will be checking eBay today.
PS. I still have not pulled the chassis. Working through the bottom of the set (cut away all the particle board that had air wents and removed) with the set face down.

Thanks again for your help and advice,
Carl

A possibility: perhaps dropping the set actually broke the glass on the damper tube? I recently repaired a portable color set with several cracked tubes; when they were replaced the set worked fine. I also recall that the H.O. tube on my CTC-5 cracked when I moved it (gently) from one end of the house to the other. Does the tube look foggy white inside? Look for a crack around the base. Try a new tube in there and see what happens. You shouldn't have trouble finding one-pretty common. I would buy it from www.radiodaze.com but there are plenty of good sources.

Hey, Bryan,

The tube has no fog in it. It has an uneven dark stripe around the base, but it's smooth. Not sure if completely smooth glass could have a crack in it or not, but sure hope so in this case.

I got a damper tube NIB on ebay for $2.00. It should be here tomorrow or Thurs. Will update.

Thanks, Carl

Update #3:

Indeed, the new 6CL3 damper tube works and has lit up the screen, but nothing more. Just a white, lit up, blank screen with no audio.

Ironically, when I pull the 12HG7 video output tube out completely (the genesis of the problems in my opinion), nothing changes. Same white screen, no audio, except for the usual low frequency hum at full volume. The tube V/O lights up though when plugged in. When I wiggle it, I can hear static on the speakers and I see one of the pins (through the glass of the tube) sometimes display a small electric spark for a short time.

I've also noticed when I touch the chassis, this low frequency humming sound diminishes to some degree.

The video output tube plug plastic is cracked and pieces have chipped off. The bottom contacts for it have been re-soldered, but I think I need to replace the plug. No idea where to get one though and not sure I am good enough to replace the plug without causing more damage! ;-)

Thanks for helping solve my little puzzle here!
Carl

Just a white, lit up, blank screen with no audio.

First, I'd check to be sure the IF amp. tubes are good, and that they're connected in the socket, I think a bad or not lit up IF tube would cause that. As for the vid out tube socket, I've never had to change a tube socket on a circuit board before, but I'm sure someone here has. On one of my sets that uses circuit boards, some previous repair man had soldered a new socket ontop of the old one, to avoid damaging the board further, it doesn't look pretty, but it seems to work ok.

On CTC-38's the IF stages are transistorized. I have seen a power supply problem knock out the 80 volt supply to the transistors and thus cause no video or audio. The last time I fixed the problem there was a bad wire wound resistor in the power supply near the filter caps.

On that tube socket repair I have done like Adam said just used a regular chassis mount socket. I busted up the old socket and used a desoldering wick to remove the old contacts. Then I soldered long bare wire to each pin on the new socket, put the wires through the holes, solder at the board then run the bare wire back the PC board trace to the next connection point and solder there too.

"On CTC-38's the IF stages are transistorized."

oops, sorry for the confusion, I've just seen a few sets lately with that same problem caused by bad IF tubes, so I had that on my mind.

Thanks. Would the V/O tube's having no effect on the white screen/no sound issue whether it is plugged in or not likely mean something is not right with its socket/socket connections (the tube is OK), or perhaps be more about the IF stage transistors being cooked?

I'd really like to try and repair the socket, but not sure if there's an easy way to do it. It's not in that bad of shape yet. If I pop the socket out, can I ask what I should look for to see if it is in working order?

I just don't understand how the tube could light up, but have no effect on the problem, plugged in or not....

Perhaps I need to find and solder more ground connections between the PC boards and chassis?

It's time for the real troubleshooting now, not just supposin'!
You need a schematic and go in there and check out your voltages and I would start with the supply to the IF stages. When you get past just checking tubes and visual inspection you need your schematic with voltage measurements or you will waste your time big time and be frustrated trying to find the problem.
If you don't have a copy I should be able to find one.

Chad,

Thanks, but I don't have the skill set needed here......I've never read a schematic (seen them though) and don't have the voltage meters needed. Have soldering iron will travel is about my limit. Not in the league of you all, but have a lot of respect nonetheless. My uncle was a TV repairman on the side, God rest his soul...! Never got a formal education from him! ;-)

Probably my last hope on this one is someday to get it out to Bryan Gadow's place when he's not too busy and leave it to his capable hands. Maybe someday I'll get down to brass tacks and learn proper troubleshooting and repair...!

Thanks again for all the help!!! Will update down the road.

I have a feeling that some of those tubes you bought are not too good. OR, you have some really dirty tube sockets. Bouncing the set made me think of these things. If I were you, Id resolder any PC ground points, and anything else around the tube sockets that looks dull, or you see cracks in the solder. Any chance that you adjusted the AGC control a bit too much?

You really need access to a good tube tester. One that can really work the tubes in question. At the least, your set has all its deflection and HV circuits working. Thats one BIG problem in most of the old sets I see.

Have you messed with the tubes in the tuner at all? If nothing else, try reinstalling the original tubes, except for the damper, and the other one that you found bad. Even original weak tubes are sometimes better than ebay junk. People will sell anything there, and tell you that they have tested everything, etc, and still lie to your face. These are in the minority, but they are there. I, on the other hand, have only had one bad ebay experience. The seller sold me a load of tubes that tested good on his checker, and mine, but in the circuit, they were microphonic-- tap the tube and hear it 'tinging' in the speaker! Wouldn't take them back. :tears:

One other thing, dont adjust controls that you dont understand. Your set will work again, but you gotta go easy on her. You are so lucky to have that style set. :thmbsp:

Any chance the normal/service switch is in the service position?

A lot of things to check, and lots of good advice being given here. It would be nice if it was something simple-would be a lot of trouble to bring it down here, and then the pressure would really be on me to figure it out! Ha! You could just pull the chassis in that situation, and I could try to rig it up to my test jig, but that is still lots of trouble.

First thing I would do, if you haven't already, is take Holmes suggestion regarding the service switch. With the set on, work it back and forth a few times and see what happens. These get dirty contacts and cause problems.

Hi,

A few answers/questions:
Spun the AGC screw around a few times both ways, no difference.
The service switch--same thing (had messed with that one in the past too).
Is it possible these new tubes could go bad so quickly after working so good?
(putting all the old tubes back in will be next project if the answer is Yes).
Most tubes light up strong with blue halos inside.
Have wiggled most of the tubes around a bit while the set was running, but no difference except for the 12HG7 V/O--loud popping sound in the speakers. Still see that spark in there under one pin.
Did try this too with no change or improvement:
Ground up some steel bar on the grinder to get metallic powder. Carefully dumped some of it in the 12HG7 tube socket holes to get better contact in there. Didn't help nor hurt. Removed most of it with a magnet.

Bryan--no pressure, promise! You could take as much time as you wanted. At least I know the CRT is still good. If that hadn't come back on after the new damper tube was installed, I'd probably bag this one.

PS, should I spray contact cleaner in that service switch and try again?

Thanks again for the advice and have a great 4th!

Carl

Update #4:

Replaced all the tubes with the old ones....got the same white screen, but a bit dimmer and smaller with a black area at the bottom. Wavy, unstable illumination as well. Contact cleaned the tube sockets and service switch too. Replaced the new tubes again and back to stable white screen.
I also remember as the set was failing, when I changed VHF channels, the screen would go completely black for a split second before illuminating the channel. That only happened for about a day before it went totally kaput. No idea if that's a telltale clue...!

Thanks, as always!

Carl

If I were you, I'd re-replace the old tubes and when you see the dark area at the bottom of the screen again, replace the 6GF7 vertical output tube with the new one that you have onhand. Leave all the originals in place, and continue to troubleshoot. Check your soldering, as you can easily have a solder bridge somewhere. I thinks you really need to pull the chassis and tuner so you can see whats what, and DONT grind up metal shavings to check the tube sockets. Metal shavings are BAD!

Chances are that most of your original tubes are probably still good. Ive seen some 45+ year old tubes that still check in the high GOOD area after some tubes in the same sets have been replaced again and again...

No points for creativity on the metal shavings thing, huh? ;-)

I thought my V/O tube was a 12HG7....is 6GF7 one as well?

I should specifically check the solders underneath that one, no?

The 12HG7 is your video output tube. The 6GF7 is the vertical multivibrator/output tube. I still think that there are either solder bridges, or some bad connections somewhere. Best of luck to you.

Thanks,
I will update the next time I get to tinker with it.
Happy Friday.
Carl