Author Topic: Magnavox Stereo Theater 1MR418M restoration  (Read 8260 times)

electra225

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Re: Magnavox Stereo Theater 1MR418M restoration
« Reply #330 on: November 18, 2018, 12:16:35 PM »
My friend, the cabinet refinisher, in Missouri called this morning.  He is 95% convinced that the cabinet on the Stereo Theater was originally finished in lacquer.  This is inconsistent with what we believed in the past.  Magnavox had the bean counters working overtime in 1962, so it is very possible that the "10 coats of hand-rubbed finish" was one of the casualties of that effort.  We know that the speakers, tubes, remote control chassis and the MPX chassis were outsourced.  It has also been determined that there is a good possibility that my Stereo Theater cabinet was not built my Magnavox.  The main reason for this belief was that Magnavox used a closed-fiber type of particle board in their cabinets for sound deadening rather than the open-fiber material found in this one and that is deteriorating.  There are also joints in this cabinet that were not used by Magnavox.  The reason we believe this cabinet may have lacquer on it is by evaluating the environmental damage to the finish and by the fact that lacquer thinner easily removes the finish.  It typically requires acetone to remove the finish on a Magnavox cabinet.  Tar and nocotine, combined with less-than-ideal storage for a time seems to have damaged the finish.  In fact, mineral spirits will remove the finish on this cabinet in most places.  This discovery presents the hubs of a dilemna.  I detest lacquer and avoid its use.  So, do I refinish correctly in lacquer, or use poly and shellac like I had planned.  Or a combination of the two.  I have also found an ecap can in the HV section of the TV chassis that is marked, and appears to be a two section cap.  The parts list in Sams shows a three-section cap.  Another Sams error or do I have a "Mystery Magnavox" like others on this forum have.
I don't need Google.  My wife says she knows everything.

TC Chris

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Re: Magnavox Stereo Theater 1MR418M restoration
« Reply #331 on: November 18, 2018, 12:43:11 PM »
My '56 devices and the 1951 +/- one have lacquer finishes too.  It was the standard furniture finish of the time.  On my old radios that are in rough shape, I tend to use oil-based varnish.  Not spar varnish; that is softer so it can accommodate wood movement that comes with a marine environment.  Interior varnish.  I like it because  can brush it on and then wet-sand it  and polish it up with pumice and rottenstone (or automotive rubbing compound if that's wat's at hand). 

Lacquer finishes can be rubbed out too.

And if you have somebody else doing it with proper equipment, it would be like-new.  Or if you have spray equipment and an adequate booth.  I just like the brushed varnish because I don't have that stuff.

At least one of the under-bumper valences on the Chevy still has acrylic lacquer that I sprayed on using a vacuum cleaner and its spray attachment (!!).  I actually got pretty good at wielding that device when I was in high school.  Maybe that was the original HVLP device.

Chris Campbell

electra225

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Re: Magnavox Stereo Theater 1MR418M restoration
« Reply #332 on: November 18, 2018, 02:12:05 PM »
This one will likely get a lacquer finish when all is said and done.  Lots easier than poly if you do it right.  Not very durable, and we have cats..... ;)


I have the resistance measurements done on the chassis and have gone back over resistances that appeared out of range.  Most of those can be attributed to bad tube socket connections and/or aging components like resistors and capacitors.  I have not found anything shocking or "terminal" yet.  Just lots of little faults that, put together, would render this chassis as a non-working TV.  I am using parts of two diagrams, Sams 591 and Magnavox factory literature.  The Sams' document is a little easier to read, the Magnavox document is a little more correct.  Why would I use a diagram that is wrong, you ask?  I have actually found them both to be wrong in a couple instances.  I am working on a "Maggotbox".  I have already found a resistor on the 6GW6 Horizontal output tube, that is different on the chassis than what is shown on the print.  I believe the one on the chassis to be original, so I'll go with its value rather than what is on the print.  I have a hunch that this is not the only instance where I'll find something similar.  So far, so good.  "Gloriously Complicated"......   :) ;)
I don't need Google.  My wife says she knows everything.

Bill

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Re: Magnavox Stereo Theater 1MR418M restoration
« Reply #333 on: November 20, 2018, 07:46:22 AM »
"Gloriously Complicated" and a "Mystery", all rolled into one.   ;)

Bill

electra225

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Re: Magnavox Stereo Theater 1MR418M restoration
« Reply #334 on: December 02, 2018, 03:12:58 PM »
I have been measuring resistors.  After running all the circuit resistance measurements, I went back over everything and figured out why any out of spec resistances were like they were.  I have been measuring resistors on the individual circuit boards and have not found all that many out of spec.  Maybe less than a dozen so far, out of 40 or so.  I have two 3900 ohm resistors, in different circuits and on different boards, that test zero ohms.  That seems too coincidental to me.  I will investigate further. 


My "operating" conditions are not optimal.  I sure miss my bench.  I also understand why TV guys like jigs to mount the chassis on.  If this thing works after being restored on a card table...... :-[
I don't need Google.  My wife says she knows everything.

electra225

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Re: Magnavox Stereo Theater 1MR418M restoration
« Reply #335 on: December 02, 2018, 05:42:51 PM »
I'm ready to put a parts list together.  I believe I can do this in two orders.  It may not be as bad as I first thought.


I have some clean-up work to do, including figuring out what the deal is with the two 3900 ohm resistors that check open.
I don't need Google.  My wife says she knows everything.

TC Chris

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Re: Magnavox Stereo Theater 1MR418M restoration
« Reply #336 on: December 02, 2018, 06:31:51 PM »
Well, if they're in the same device and have the same value, they were probably manufactured in the same batch.  Maybe there was some glitch that day.  Or it was Monday, or the company got a bad delivery of carbon, etc.  Maybe you should replace ALL the resistors of that value.

And the card table... that was my workbench for the Chevy carb rebuild, too.  The engine rebuilder (a wise man) rechecked my work and found a float bent a bit outwards so it was catching up on the bowl.  I blame it on bending over the card table.  Surely couldn't be my own ineptitude.

Chris Campbell

electra225

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Re: Magnavox Stereo Theater 1MR418M restoration
« Reply #337 on: December 03, 2018, 11:38:15 AM »
This TV could not possibly have worked in the condition I got it.  It may never have worked right.  The card table is at an odd working height.  I reckon my radio bench would make a lousy card table, in fairness.  I reckon they call it a CARD table for a reason.  They don't call it a TV chassis table for a reason.   :)


And, it may not work right after I putz with it.  I have to keep a good thought.   ;)
I don't need Google.  My wife says she knows everything.

TC Chris

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Re: Magnavox Stereo Theater 1MR418M restoration
« Reply #338 on: December 03, 2018, 06:29:28 PM »
Well, as long as you get your capacitor polarities right and don't connect something to the wrong lug, it's not likely to work WORSE.  And even if it's not perfect, you can always track down an old-TV guy to do the final diagnosis and repair, the kind that requires specialized knowledge and tons of experience ("That's the model where the IF transformer always went intermittent," that kind of thing). Then you will have narrowed the possible defects way down.  Like the open resistors.

Chris Campbell

electra225

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Re: Magnavox Stereo Theater 1MR418M restoration
« Reply #339 on: December 04, 2018, 02:41:04 PM »
I'm the only "old TV guy" in my neck of the woods for several hundred miles.  This has been a learning experience for me that I have looked forward to for a long time.  I'm not sure if I'll ever work on another TV, but I want to do all I can to get this one going as well as I can.  I appreciate the confidence you have in my ability.   :)



I don't need Google.  My wife says she knows everything.

Bill

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Re: Magnavox Stereo Theater 1MR418M restoration
« Reply #340 on: December 05, 2018, 07:35:07 AM »
Speaking for myself, and I'm sure others here on the forum, we are routing for you.  And when you get this on under your belt, the skies the limit.  ::)

Bill


electra225

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Re: Magnavox Stereo Theater 1MR418M restoration
« Reply #341 on: December 08, 2018, 11:28:01 AM »
I have measured all the resistors in the TV chassis.  I am using a calculator to figure out the percentage of drift I measured.  An odd fact I have found is that all the resistors I've calculated so far have drifted tenths of a percentage on either side of 9%.  There are those that should have closer tolerance than 20%, so these I'll go back over to determine if they are far enough out of tolerance that they should be replaced.  I'll note which these are and will go accordingly.  I was expecting more out-of-tolerance resistors than I'm seeing so far.
I don't need Google.  My wife says she knows everything.

TC Chris

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Re: Magnavox Stereo Theater 1MR418M restoration
« Reply #342 on: December 08, 2018, 12:19:31 PM »
Maybe I'm just fumble-fingered and inept, but it's awfully easy to damage things when replacing soldered components.  Some of them can very very hard to disentangle, even with good desoldering techniques.  Maybe it's best to focus on just those that are way out of spec, especially where the specs called for close tolerance, indicating a critical component.

Chris Campbell

electra225

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Re: Magnavox Stereo Theater 1MR418M restoration
« Reply #343 on: December 08, 2018, 01:47:48 PM »
I have gone back thru the resistance to ground on the low voltage, sound, IF, and sweep boards.  The reason resistances are off is due to the poor solder connections on the 6GC5 voltage divider tube.  I have run back thru the individual resistor measurements and have investigated any that were out of tolerance.  The 3900 ohm resistors I thought were open actually were okay.  One should be cognizant of meter settings when going from megohms to lower ohms.  I did not have my meter set correctly, and therefore got wonky readings.  This is where having my typical five or six VTVM's fired up at once on the bench is of advantage.  I avoid such errors.  No harm was done except some wasted time and some skinned-up pride.  I have done the LV, sound and IF boards with the individual resistors and have yet to find one out of tolerance.  I believe, at this point, that if I recap and fix that socket with the bad connections, I will be closer.  I wonder if this is a fairly low-hour chassis that has suffered from "happy hands at home" considering that wholesale replacement of all the tubes.
I don't need Google.  My wife says she knows everything.

electra225

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Re: Magnavox Stereo Theater 1MR418M restoration
« Reply #344 on: December 08, 2018, 02:38:59 PM »
I have gone thru the resistances to ground and resistors on the sweep board and the HV section.  Like previous boards, the resistance to ground readings are acceptable, considering the bad socket connections on the 6CG5 tube.  Is it possible there are NO resistors in this entire chassis that are out of range?  Is it even reasonable to consider the fact?  I have lifted one end of certain resistors that appear to be out of tolerance when I found they were in parallel with another component.  All have been okay up to this point.  All have been within 10% of spec.  Certain resistors with closer tolerances have been checked and have been found okay.  I suppose when I get the chassis back into the cabinet and connected to the CRT, I'll discover how accurate my work has been.  I checked more than once.  Hmmmm....... :-[


The plan right now is to get my parts order finalized and get the parts.  I'll recap the chassis first, then do the electrolytics last.  I have to figure out a way to get the high voltage cage off before I can restuff one of the electrolytic can caps.  I'll recap and clean, recheck my work ad nauseum, then take this thing home in the spring and see what happens.   


My first idea was to replace every resistor and every capacitor that was not a ceramic disc in this entire chassis.  Cooler heads prevailed and suggested that more harm to the PC boards might be done than might be gained by such a plan.  If my work so far has been accurate, replacing every component would have proven a huge waste of time.  If I have to dig this chassis back out of the cabinet to redo my hack by not changing everything, I may not be too proud of myself.  "Gloriously Complicated".......... ;) :)


I have learned that the folks who work on these things with more experience than I have (everybody on the planet who works on these things! :) ) leave cleaning controls until the chassis is powered up and a fault has been found.  I don't want to fool with the settings in high voltage and that and upset the operation of the Magnalux system.  I have a vague idea of how it works, and know just enough to leave it alone until I have an issue.  Then I'll ask for suggestions on how to proceed from that point.
I don't need Google.  My wife says she knows everything.