My Stereo Theater TV chassis

[electra225]

Mostly, yet partial, success! I have high voltage with a nice, full raster. I have no audio at all. I believe I may have video, since I have snow on the screen. When I change channels, I get a flash on the screen, so may I assume the tuner is working? The audio detector tube is fed B+ from the boost line. I need to verify B+ on the audio board. From what I can tell at this point, the horizontal and vertical deflection appears to be stable. I can see the lines on the top of the screen are wider than in the middle of the screen, so vertical height or linearity may be off a bit. I can connect the Analyzer to the antenna terminals, then see if I can get an image on the screen. Fine tuning may still be off, since I have no idea where it is.

[William]

Success, or at least partial success is a good thing. The rest is just around the corner.

Bill

[electra225]

I need to get an image on the screen, then determine why I have no audio. I forgot to mention it pulls 315 watts with the TV powered up now. It only pulled 250 watts with no high voltage. This thing will heat the shop almost as well as the Concert Grand does. I was sure glad to see the picture tube light, I can tell you that. The shield wire that was disconnected made a difference, I think. I just can't tell what difference it made until I get sound.

[TC Chris]

What are you using to feed it video?

Chris Campbell

[electra225]

I haven't gotten to feeding it anything yet. I got the final repairs done to the chassis and the chassis installed into the cabinet fairly late in the afternoon. I wanted to see if I had a raster and whether I had video and sound. The plan is to feed a signal at the video IF via my 1077B TV Analyzer. The first thing to do is to verify B+ in the IF strip and sound boards. Then I'll feed the IF signal to the grid of the first IF tube and see if I have an image and sound. I think that device will send a test pattern at IF to the video amplifier and an audio note at 1000hz to the sound amp. If all is well there, this puts the tuner under suspicion. Tube wiggling would be appropriate for the tuner tubes. They face forward so are inaccessible from the rear of the cabinet. I can remove the 12" speaker and gain access to the tuner tubes without removing the tuner. The tuner end of the cabinet is incredibly crowded with the TV tuner, radio tuner, both speakers, the MPX and the remote chassis all on one end of the cabinet.

[electra225]

More success! I'm getting closer to actually watching TV! Well, to be honest, I can now WATCH, what I meant to say was I am getting closer to watching AND listening to TV. This image is the most beautiful image I have seen on a TV screen in a LONGGGGGG time. Egg-shaped and out of focus though it may be, it is still beautiful. I have absolutely NO sound. The good news besides having an image, is that I fed the output of the Analyzer into the antenna terminals. This proves the tuner is working, so I don't have to remove it. YEA!!!!!

I'm not going to do any tuning up of the image until I get sound. Vertical height is off, maybe linearity as well. Width may be a bit fat as well. Still draws 315 watts. Seems like it takes a long time for the picture tube to light, but it's been awhile since I messed with an old tube B&W set. The image is stable, the vertical and horizontal lock in approximately the middle of their range. I can hear the vertical running. The horizontal makes a little squeal, but not all that much. I'll run some voltage checks on the sound board, then report back. I am beyond thrilled so far....

[electra225]

I am temporarily stuck. I'm not having any luck troubleshooting the audio section. The 1077B has a feature that injects audio for diagnostic purposes. I'm not sure if this is modulated at the IF frequency or not. I've tried injecting this signal into the audio IF tube grid with no success. The audio section in this TV chassis is different from a radio. Sound on a TV is FM, so there is that. The voltages I have checked have been okay. I made resistance measurements and find nothing open. I'm going to need some guidance on this one.....

[electra225]

I have been reading....

"Muting receptacle (when used)"......This on the "alternate sound circuit" drawing, which my set has. I have been going thru the audio section, component by component. There is a black wire with an RCA jack that connects from a point on the chassis, above the sound board, that goes to a switch on the back of the tuner, connected to the motor that runs the tuner via the remote control chassis. I will now access the information that Paul, one of our members sent me years ago that explains the workings of the remote control system. This black wire has always appeared to be out of place to me. I also noticed that the contacts on this switch are closed. Could that switch, if it is indeed a muting switch, and since it is closed, can that be killing the audio? The audio is stone cold dead. I can't pull the tubes and make noise in the speaker. I have grounded grids, no noise. I have never seen a deader audio section on anything in my life. Methinks I will hie to the shop and disconnect that black wire, power up and see if I get the audio back. This is silly enough to actually be the issue.....

[electra225]

Guess what......

I have audio! Scratchy, noisy snowy audio, but audio and from both channels of the stereo, no less. Channel 3 output from the Analyzer actually comes in better on Channel 4 on the TV, but the fine tuning on this thing is bizarre. Almost impossible to get a grip on the knob to turn it. That silly mute switch on the motor is shorted, killing the audio. I still have some tune-up to do yet, adjusting vertical that kind of thing, but I'm done for today. My next step is to connect a DVD player and make adjustments of fine tuning and that from it. Part of the reason for the distorted image on the TV is that my Analyzer is not working right. I suspect a control I didn't get clean enough. I need to adjust the horizontal on the Analyzer. But, progress has been made, success may be just around the corner. I am thrilled to be this far and have been blessed in my efforts.

And, just as a P.S., to the member who provided a useable schematic for this chassis, you'll never know how important that turned out to be on this project. I could never had muddled thru this without that drawing. I won't mention any names in order to protect the innocent. I wanted to thank him publicly......

[William]

CONGRATULATIONS, GREG! That is great news, and sometimes we get lucky with the repair being so simple we overlook it. I can't be happier for you. Once it is truly up and running maybe you can take a video and share with all of us.

Bill

[electra225]

I'll have to learn how to do a video. I've never done that before.

I thought I saw a flash in the damper tube last time I fired it up. I'm not going to buy trouble. I'll retest that tube and may get another one to have just in case. Of course, I sold all my TV tubes at the auction......

It takes a long time for the picture tube to light, it seems to me. Maybe 30 seconds after I turn it on. It comes up really gradually, not all at once. That may be normal. I'm used to the flat panels like everyone else.

After I watch the Ronald Reagan movie I use for test all the way thru, then I can breathe easier. There was a lot wrong with this TV and I have a minimum of equipment. The Analyzer proved its worth. If you mess with an old TV you surely need one. Even if it is not 100% it will provide signals and an image you can use to troubleshoot a set. I believe I'll look for a high voltage probe and a tester you can use to measure cathode current. You unplug the HOT, plug in the tester, then plug the HOT into the tester. The tester does TV HOT's and certain audio output tubes. I have my parents' first TV, an RCA, one of those with the vertical chassis that is hard to work on. Haven't had it powered up in probably close to 40 years. It worked fine last time I used it. I also have dad's last new TV, a 1967-ish Warwick-built Silvertone console a 23 or 25 inch.

[William]

Greg, what number tube are you looking for?

Bill

[electra225]

6DA4. The one in there is a NOS RCA I put in when I repopulated the tubes. The one in the TV when I got it was a dead 6AU4. I took a day off from TV repair. My mind was shot after chasing my tail for so long trying to figure out the audio issue. I'll get the GE stereo done, then get back on this set. I want to make a new back for the cabinet like I did for the Concert Grand. I have the pattern done and cut out. I need to go to HD and have them cut a piece of lauan then find some wire mesh. The Stereo Theater makes a lot of heat when the TV is on.

[William]

Is the 6AU4 a sub for the 6DA4?

Bill

[maxidyne]

Allegedly. This set uses tubes that are not commonly seen. I should probably go with the specified tube and not press my luck. The tube substitution manual says the 6AU4 may not work in all circuits.

[electra225]

I connected an old VCR to this set today. I was watching a cut rate version of the Beverly Hillbillies. I say cut rate because it doesn't use the original theme song, which I wanted so I could check the audio. The audio on this CD is really chintzy, I can tell you that. I don't get any hum or buzz between scenes, the vertical and horizontal are rock solid. I may have a tad of horizontal pulling on the right side of the picture, but that may be due to the "not the best" CD I was playing. The picture is beautiful. The TV guys say a "Maggotbox" is not worth working with, but this thing is impressive. I could use a 1/4" more vertical deflection, but I'm not going to mess with it. The picture tube tested weak when I started, but it produces a beautiful picture with good contrast and no ghosting. The picture does not bloom when I crank up the brightness, so I think the picture tube is just fine. This thing pulls 320 watts, all 36 tubes are hot when the TV is on, even the Multiplex adapter. This TV may not be in the Zenith category as to performance, but it is at least the equal of RCA. I'm happy with it. I ran it for about an hour. We'll let it cool down, then start it again. If it starts and runs again, I'd say we are home free. The fine tuning was one channel off. When it was tuned to channel 4 you get picture on channel 3. I adjusted that and it seems fine. The tuner doesn't appear to be dirty, nor the fine tuning control. I person, the picture is lots better than in these photos.

[William]

Congrats, Greg, it looks great. Now, was this the last task, or is there still more to do to your Magnavox Stereo Theater??

Bill

[electra225]

All that's left is the changer. I'm not going to do anything with it, at least in the short term. The VM changers I have are so much fun, I don't see much use of having so many changers that work. I can figure $100 per changer to tune one up. Then they'll set around and get all stiff and messed up again. Maybe later. I want to get the ones in the Imperial and Concert Grand going first. I'll make a new back for the cabinet, since it generates so much heat. A little extra ventilation can't hurt it.

[Hi-Fi-Mogul]

Super nice work, Greg !

Granny approves of that "fancy washing machine" !

[electra225]

I need to get the wife to hold a mirror so I can adjust the vertical a tad. This is the first and only TV set I have actually repaired that was broke. The only real faux pas was the deal with the mute system. I should have looked more closely, or paid more attention to the detail in the drawing. Next time, I will compare what I see to the drawing, then investigate anything I may not understand. My next TV activity is to try and get a signal over the air on old TV sets.

I also learned not to put much store in what a picture tube tester tells me. I'll use mine to see if the filament lights, then do a start-up to see if the picture tube lights. My guess is if it lights, it will produce a picture.