Sometimes you should stay in the house......

[electra225]

I thought it would be a good idea to move my collection around to give the shop a different look, and I wanted my TV sets in one general area. I fired up my 1ST616 "Concerto" and tried to play a LW record. It played fine for about ten minutes, then the music quit. The platter was still turning, but the amp had quit. When I put the function switch in "Stereo" which operates the record player, the amp is dead, but the platter spins. Function switch? Is it possible the power switch on the changer might be wonky, putting power to the phono motor, but killing the amp?

Next, I decided to fire up the Stereo Theater and watch a Dick Van Dyke movie. It won't sync horizontally. Everything else works okay, just no horizontal sync. It will ALMOST sync. I need to see if there is a horizontal frequency adjustment on the chassis. I have a nice clear picture, good brightness, good contrast, tuner works okay, good vertical sync, right in the middle of the control. It's been six months or so since I had it on. I remember the horizontal hold being really touchy then. I thought for a minute that maybe the sync detector diode that usually goes out might be on the fritz, but that would also affect the vertical. I should probably test/sub the horizontal oscillator tube, a 6CG7/6FQ7. I'll pull the schematic and see if I can learn something there. I realize I don't use a tube CRT TV set much, but it seems like it takes a really long time for this set to come on. Maybe a couple minutes before I get sound, even longer before the raster comes on. The screen fills out, so one would think B+ is okay. If the horizontal oscillator tube was lazy or weak, that could affect the high voltage coming up, as well as affecting horizontal frequency, and horizontal lock.

If you don't use this stuff regularly, i.e. at least once a week, something always goes on the fritz. I think the issue with the 616 will be the more serious. I'm not looking forward to cleaning and especially replacing the function switch. It may just keep a busted record player. I have plenty others I can use. Sometimes, I should just stay in the house.......

[electra225]

I have a scanned copy of the Magnavox factory literature for this TV chassis. A member of the forum sent me this information and it has bailed me out numerous times. It is about to again. There are a couple of diodes, called sync detector diodes, that are a high-failure item. These tested and proved good when I got this chassis going the first time. The horizontal hold control was always set to almost the end of travel, so the horizontal frequency was right on the ragged edge all along. I was advised to change those diodes out of hand, don't test them, just assume they are bad and CYA. But noooo. I knew better than that, I was lots smarter than the guys who knew what they were talking about and were sharing their knowledge for free. So here I am, in duck soup again. Probably self-inflicted this time. There is a horizontal frequency control that may need to be moved a bit after I get the diodes changed.

The record player situation is a bit more mysterious. No schematic I have shows exactly how the phono motor and switch are wired in relation to the amp. I assume there are two wires out of the phono switch, one for the motor, one for the amp. The switch on the changer and the function switch are wired like a three-way switch. The situation is not changed by manipulating the function switch. Whatever happened is a hard failure, it's not intermittent. I'm still looking at schematics, maybe one will show me what I need to know.

[electra225]

The phono motor on the 616 will run any time the main power switch on the tuner is on. I really believe the problem is the function switch. If that is the case, I'll find another tuner with a good function switch then just switch tuners. I'll pull the tuner to verify my suspicions.

I need to start from Square One with the TV in the Stereo Theater. I found a couple of other "bugs" in the operation of the TV I should investigate. I'm going to change the phase detector diodes that I should have changed when I had the chassis out. Then I need to check B+ at the cathode of the rectifiers. Then I probably am going to have to adjust the horizontal frequency control a bit. Retouch vertical height and linearity controls. The controls on the rear apron of the cabinet are dirty, particularly the brightness control. Running this chassis as long as I did may have caused other original components to fail. I didn't change filter caps, they checked good. Now, I'm not so sure that was wise. I have more questions than answers at this point.

[TC Chris]

Maybe check the mute switch on the changer before getting too far into other causes?4

Chris Campbell

[electra225]

According to the schematics I have, the phono power goes thru a Molex connector to the changer. I don't see any connection to the chassis, but there has to be one, else it wouldn't turn the amp off after the last record has played. The phono motor still runs. Whatever happened was sudden. I wasn't having any trouble. I had played a stack of demonstration records on it just last week, worked fine.

[electra225]

The worst part about both of these failures is that I have to pull the back off the cabinet to troubleshoot. Magnavox put the back panel on a jig, then built the instrument around the back.

The first thing to check on the 616 is the connections to the power switch. On the Stereo Theater, I'll probably pull the chassis, AGAIN, so I can check a few things. I may change the filter caps just because. I may also change the rectifiers, again, just because. I suspect low or unstable B+. More on that later, and I may be wrong. Then I want to change the phase detector diodes, which should have been done before now. I also need to finish the hotrodded back, made like the one for the Concert Grand. I can't see thru the original back well enough to see if a tube is red-plating. I don't want to have to pull the back just to see the tubes every time.

Bob Andersen uses these things. Adapt-A-Cap. Like restuffing a can, but with free-standing capacitors. I'd like to try them.

https://adapt-a-cap.com/

[hermitcrab]

Greg, sounds like the problems I am having with my sets .... they all are starting to exhibit electronic and mechanical problems, guess those 60 year old caps are finally giving up the ghost. My Imperial Astro sonic has one channel almost unhearable unless you crank the volume, when I do, it sounds good, so I doubt it is a transistor, more like the coupling caps are failing...My fisher regent same story one channel is low but not dead , another case of dying caps. My silver tone also has a weak output channel. the other day I decided to play an album on my home-built fisher and the Dual changer is acting like the motor is failing , takes forever to get up to speed , not sure if these have a run cap to help start the motor or not I can't remember, so I guess I got to dig out the schematics for all these sets. I was living by the shango rule if it isn't broke don't shotgun parts ... But I think that needs to change, total recapping is the only way to get another 15-20 years out of these without having to worry about them. but out of all my sets, these are the only ones giving me grief. The sets built with ceramic caps are all still chugging along just fine ...aka like my Motorolas

[TC Chris]

My Heath device had one channel that only made noise when the volume was cranked up. It was a failed resistor that caused off-spec bias for the driver transistor on that channel.

I complicated the diagnosis by installing a red-red-orange resistor wen I wanted red-red-red. Replacing a bad resistor with the wrong value did not improve biasing. In my defense, the red and orange paint on these devices is very similar.

In any event, do some voltage checking. It's easy when you have one good channel: compare voltages on that one with what you measure on the other.

Chris Campbell

[electra225]

The problem with the 616 is in the tuner. I'm not going to pull it all apart right now.