Repair of 1961 Magnavox 1ST616 stereo console

[electra225]

I redid this stereo several years ago. It's been working just fine up until it wasn't. I was playing a record when I suddenly lost the amplifier. My quest is to figure out why the amp is dead in the "Phono" position of the function switch. Typically, one would find a switch mounted on the rear of the function switch that works as a three-way power switch with the switch in the changer. I'm not going to offer any guesses until I get a bit more information. I have the entire stereo on my bench. My idea is to remove the tuner without removing any wiring so I can test it under live conditions on the bench. This procedure would be ungainly done on the floor. Pictures to come.

[electra225]

The first challenge I have, typical of Magnavox, is trying to decipher their "componentized" schematics. I have a schematic for the tuner, one for the MPX, one for the amp, but they don't make one with everything connected. I'm trying to figure out exactly where I look for the problem I'm having. First guess suggests there may be a switch on the rear of the function switch that works three-way with the power switch in the changer. First guess also suggests that, if this switch is open or broken, why can't I just jumper it and move on? First guess also asks what would happen if I did that? A short circuit? Nothing, except the stereo won't shut off after the last record is played? If I jumper the switch, what happens to line voltage? Will it run in a redundant path with the function switch, or will it bypass the power switch for the console, in tandem with the treble control? I don't see on any schematic I have how the changer power switch relates to the one possibly on the function switch. Hmmmmm....

[electra225]

This isn't the schematic for my stereo tuner, but it shows how the changer is wired in to the tuner. There does appear to be a switch on the back of the function switch that powers the amp in the Phono position. Looks to me like I can jumper the switch if it's bad and all that will do is to prevent the console from shutting down after the last record.

[TC Chris]

Eliminating the auto shutoff in not a bad thing. Tubes don't really like shutoff/turn-on. The fewer the off-on cycles, the better.

Chris Campbell

[William]

If you remember a few years back I had the same problem with my Imperial. I reached out to Mark O. and he told me he had a switch that should work but when it arrived it was not correct and no matter what I did it just would not fit. So, I installed a toggle type switch on the back of the console, you can hardly see it, did some bypass surgery and it functions in the same way as the original switch on the back of the function control. I actually like it, for the same reasons Chris mentions. I can put on a stack of records, play them and when done the changer shuts down but the electronics stay on so I can continue to play stacks of records keeping the electronics alive. When I decide to play the last stack I flip the switch and when the last record plays the system shuts down. Works great and I wish I had that option on all of my machines.

Bill

[electra225]

Well, guys, I fixed it! I'll have to admit I got lucky. I've lost my "edge" in my old age and sometimes I chase my tail. This time, I made the mistake of trusting my testing. I took a break and decided to approach this from the "does this make sense" angle. The switch checked good. Put power on it, the thing would run for ten seconds, then go dark. That did not make sense. EVERY test I made showed it should work. So, I removed that switch, brave soul that I am. I gave it two doses of contact cleaner, and one does of WD-40. Guess what fixed it. Right. The WD-40. The record changer sounds like crap. There is a lump under the platter mat and it sounds like it is mono. I think the trouble there is I have some possibly dead tweeters. I just never could get the audio in this stereo bright enough. While I have it apart, I'm going to investigate that. Then, I'm going to go thru the changer again. This thing has an EV 26 cartridge, so it should sound magnificent. Then, I'm going to change the grille cloth. Again. When we refinished the cabinet, the wife thought burlap on the speakers would look cool. It does, but the black has faded out to almost bare burlap and it looks awful. I'll order some real black cloth from Parts Express like I used on the ST. I have pics, but supper is ready and I don't want to be late. More later.....

[electra225]

Pictures as promised.

This is the victim. Nice, sloppy Magnavox wiring.

Model number sticker.

88 series amplifier.

Code 137 tweeters/midrange speakers, Chicago Telephone Supply.

Tuner model number 59-24-00

I had to remove a tube from the Multiplex adapter in order to remove the tuner. Good luck getting that tube back in with the tuner installed.

The tuner sets on these two cute little metal brackets. Two bolts on top hold it in place.

This is the switch that caused all this work. Apparently, it was just dirty and not making good contact. Time will tell how this theory works out....

The first test drive after repair.

The little "lamps and lighties" glowing brilliantly....

[TC Chris]

Of course, if all the wires were bundled up and harnessed mil-spec style, we all be griping about what a PITA it is to undo it.

Chris Campbell

[electra225]

Another tidbit of information I learned by looking at the schematic.....

A possible reason this stereo "sounds like it's mono" is because the balance control does not control the output of the amp to the speakers. It controls the signal to the amp. If the control is turned too far in one direction, it will attenuate that channel input. Some dummy (!? ) has the balance control turned almost all the way to the left. I need to rebalance this control and get the signal where it is stereo again. You use a mono signal, put meters on each channel, then balance as best I can. I'm going to check the tweeters and crossover caps, but the "no stereo" condition may well be self-inflicted.

[TC Chris]

Is yours one of the models that had the balance control on the amp chassis, or accessed by screwdriver inside a control shaft?

Chris Campbell

[William]

Your speaker arrangement is the same exact set up as my Columbia, built by Magnavox. Mine is single ended 6BQ5's and no tuner. It is also an interesting statement in your last post about the balance. My Symphony and your 1ST616 appear to have the same 100 series tuners and my balance control works just like what you stated. That leads me to believe the 100 series tuner has that design built into it. Does that sound right?

Bill

[electra225]

As far as I know right now, yeah, I'd say that sounds right. I was playing an RCA demonstration record and it sounded "flat", with only half the music being played. One a piece with a choir, it sounded like the choir was down the hall from the recording studio. RCA demonstration records are famous for the horrible music contained thereon, but this particular one, circa 1965, is actually quite good. I don't want to risk my Magnavox records lest I mess them up with a phono of unknown condition, but I don't care about the RCA ones. According to my notes, this cartridge got a new needle when I redid the cabinet, so the record shouldn't be in any particular danger. According to what I've been able to deduce, the balance controls on the amp chassis control the strength of the output to the speakers. The balance controls that are accessed thru the hollow shaft of the bass control, attentuate the strength of the signal to the amp. The balance control in this 616 is pretty dirty, shock, shock. Maybe a general control cleaning would be in order as well.

Chris, this stereo has the balance control accessed thru the hollow shaft on the bass control.

[electra225]

One step forward, two steps back......

I kinda sorta fixed the power switch on the back of the function switch. About every third time you turn it on, it won't work unless you fiddle with the knob a bit. Getting better, though. I cleaned all the controls. Before cleaning, when I turned the bass control to minimum, it would kill the Channel 2 speaker. Plus, in order for both speakers to work, the balance control had to be set completely toward the Channel 2. Now, the control is almost in the middle and I have it back to being a stereo again. I checked the tweeters. They seem to be working well. There seems to be a lot of attenuation of the signal between the big speakers and the small ones. The crossover caps are supposed to be NP 16uf. I have two 33uf caps connected in series, so that should be good. I may tinker a bit more with values of the crossover caps to see if I can brighten the audio up a bit more. I also want to see where I'm losing signal between the speakers. I'm ready to put the tuner back into the cabinet.

The step back is the changer. I was playing a demo record when it just quit turning. The motor runs, the amp is on, but now the platter won't spin. The speed control is frozen. I just changed speeds five minutes ago!

So, I reckon the changer is the next step. Wish me luck, I'll certainly need it....

[electra225]

Well, I got a bit sidetracked, but I have had a very enjoyable time in the shop today. I decided to connect my cassette deck to this thing so I could set the balance better than it was. I found an old tape I'd made when we were holding dances at a local rental hall for the car club. It is all pretty hardcore country and I found it amazing that it still sounds as good as it does. Probably close to 40 years since I made that tape. Gene Watson "Between This Time and The Next Time", Tanya Tucker "Cowboy Lovin' Night", John Anderson "Chicken Truck" and "Swingin'". I connected the stereo to my 15" shop speakers. This thing will rock! I still don't have the audio as bright as I'd like it, may never have that. It has awesome bass connected to those big speakers. I really need to get to work, but I'm having Way too much fun......

[electra225]

This may be all in my head, but I swear this is the second Magnavox stereo that I have worked on recently that sounds immeasurably better after the controls were cleaned with De-Oxit. In fairness, I have never been a huge fan of De-Oxit. I find it really no more effective that the cheap stuff, plus the fact the price they want for the stuff aggravates my sensibilities. Is it possible that a dirty control such as a volume control or tone control could bleed certain frequencies out of the audio? I may have to reconsider my reluctance to use De-Oxit, particularly on Magnavox stereo controls.

[TC Chris]

In my old age, I have come to understand that sometimes the expensive stiff is expensive because it's got better ingredients or is more difficult to manufacture. And if something has a good reputation, it may be because it's better. The notion does not apply to certain fields like health supplements or miracle cures, which are mostly flim-flam.

Chris Campbell

[electra225]

The changer is not as crabby as I first thought it might be. I have no idea why the speed control wouldn't turn. It worked fine after I got the changer out of the cabinet. The motor mounts are like concrete, the platter bearing is dry. The drive tire is hard as a rock. The jury is out on the needle, my earlier notes don't mention it being replaced. The EV 26 cartridge doesn't want to rotate over to the 78 needle. The most amazing thing is that the platter mat, typically found almost solid, is nice and flexible. The reason it was lumpy is that one of its little feet that went thru the platter had become dislodged. I have a set of mounts, so that is a good thing. There are several detail differences between this S-600 changer and the Conquest in the CG. The motor on this one is about a third the size of the one in the Conquest. The Conquest motor doesn't have rubber mounts, this one does. The hard, lumpy drive tire, the hard mounts and the dry spindle bearing are likely causes of all the turntable rumble this thing has. A good tune up, some new parts and this changer should be good as new. I think the basic mechanism is very close to the same between this changer and the Conquest.

[electra225]

Guys, I could use some ideas. The volume from the four small speakers, tweeters and midrange, seems to be very low. I believe the speakers are okay. I can barely hear them with my ear up against the grille cloth. I connected a spare 4" speaker to the external speaker jacks and it sounds a lot better. I think my next step is to jumper the crossover caps and see what happens. Why would the crossover caps attenuate the volume so much? This setup is supposed to be a 16uf non-polarized cap for the crossover. I have two 33uf caps connected in series in their place. Something is wrong, something I'm overlooking.

I got the motor mounts changed, did a little tune up work on the changer, cleaned everything real well. Next step there is to get a new drive tire and a needle. This cartridge does not have the original needle.

[TC Chris]

Are the series caps in opposite polarities? You could jumper them with a wire if you keep the volume way down.

For the tweeters, you may be suffering from my malady: old ears with poor HF response.

Chris Campbell

[electra225]

I'm not having hearing trouble in this case. I have wimpy tweeter/midrange speakers. I'll jumper the crossover caps and see what happens. If I blow the speakers, I have some I can use. The crossover caps are wired right as far as I can tell.