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.