Author Topic: Magnavox Stereo Theater 1MR418M restoration  (Read 61684 times)

electra225

  • Hero Member
  • *****
  • Posts: 3749
    • View Profile
Re: Magnavox Stereo Theater 1MR418M restoration
« Reply #645 on: September 15, 2019, 11:49:14 AM »
Success!!   :) :) :) :)

Well, maybe partial success might be a better term.  I have most of a TV set.  I have no shorts, no arching, no red plating.  I have a nice, full screen.  It appears to have a bright picture tube.  The entire Stereo Theater pulls 301.85 watts without the record player motor on.  I have no TV audio, just a hum.  I see hash in the raster, but I don't know for sure if the tuner and IF sections are working.  The display is best described as "squiggly".  It was unstable horizonatally when the display came up, and I seemed to be able to adjust that out.  I'm guessing I have both vertical and horizonatal unstable or I have a dirty control.  There is nothing connected to the antenna terminals.  Maybe some kind of signal thru the tuner might be what I need now.  But, this is progress.  Now we get to sort the TV.   ::) :-\ :-[ ;) :)
I don't need Google.  My wife says she knows everything.

Bill

  • Hero Member
  • *****
  • Posts: 1686
    • View Profile
Re: Magnavox Stereo Theater 1MR418M restoration
« Reply #646 on: September 15, 2019, 11:55:12 AM »
Congrats Greg!   It's been a long time coming but I knew you could do it.  So what was the reason it was blowing the amp fuse?

Bill

ed from Baltimore

  • Sr. Member
  • ****
  • Posts: 483
    • View Profile
Re: Magnavox Stereo Theater 1MR418M restoration
« Reply #647 on: September 15, 2019, 01:33:59 PM »
   Sounds like you are almost there if you have a decent raster.
          A 60s Zenith B&W I looked at years ago had an open 3.9 MegOhm resistor from +Dc voltage too the AGC line. The set would play at first, then slowly go to no sound and then blank white raster with no snow. I guess that 3.9 Meg resistor from +DC to the AGC line was there to bleed off a buildup of voltage that would shut down the RF and IF stages. Your set looks like it has that "Keyed AGC" circuit that somehow turns large pulses from the horizontal output transformer and sync pulses from the video signal into small negative going AGC voltage, but I never understood how it did it, especially how it opened the gain of the set way up when there was no video signal to receive.
         With the set operating, put a DC voltmeter across that 3.9 Meg resistor and if you get snow and rushing noise back, you will know that resistor is open. I don't think you can measure it in the circuit with power off because there are too many bypass paths giving false readings. 

19and41

  • Hero Member
  • *****
  • Posts: 654
    • View Profile
Re: Magnavox Stereo Theater 1MR418M restoration
« Reply #648 on: September 15, 2019, 04:25:46 PM »
That's great!  Didn't you get a pattern generator sometime back?  If not you will probably need a digital to analog converter.  I have one from the government giveaway unopened, should you need one.
"Any sufficiently advanced technology is indistinguishable from magic."
— Arthur C. Clarke

electra225

  • Hero Member
  • *****
  • Posts: 3749
    • View Profile
Re: Magnavox Stereo Theater 1MR418M restoration
« Reply #649 on: September 16, 2019, 12:17:14 AM »
It's been a long day and I'm beat.  I'll just say this.  And I promise pictures and more information in the morning.  The short in the TV was not an actual short.  I placed the fuse in the wrong spot.  I was trying to power 300 watts with a 2-amp fuse.  Verifying all this was a grand adventure, one worthy of sharing.  My next job is to gain information and test equipment in order to troubleshoot the "white screen" issue.  But, this is progress and I am sure grateful to all you guys who pitched in with your two cents.  This project would not have come this far without all of you.  BTW, we are 75% done......... :) :)
I don't need Google.  My wife says she knows everything.

Bill

  • Hero Member
  • *****
  • Posts: 1686
    • View Profile
Re: Magnavox Stereo Theater 1MR418M restoration
« Reply #650 on: September 16, 2019, 07:38:15 AM »
 :) :) :) :) :) :) :) :) :) ;D ;D ;D ;D ;D ;D ;D

Bill

electra225

  • Hero Member
  • *****
  • Posts: 3749
    • View Profile
Re: Magnavox Stereo Theater 1MR418M restoration
« Reply #651 on: September 16, 2019, 12:06:38 PM »
I had an eye doctor's appointment this morning I had forgotten about.  I'll have to go back on my word about posting this morning.  I'll try to get it done later this evening.  Thanks for your interest.   :) :)
I don't need Google.  My wife says she knows everything.

Harbourmaster

  • Hero Member
  • *****
  • Posts: 2408
  • Long Beach, CA 90808
    • View Profile
Re: Magnavox Stereo Theater 1MR418M restoration
« Reply #652 on: September 16, 2019, 05:24:30 PM »
An old VCR or DVD player would actually be about the simplest video source to hook up for testing.
-- Aloha, Ken

No Console Left Behind!

electra225

  • Hero Member
  • *****
  • Posts: 3749
    • View Profile
Re: Magnavox Stereo Theater 1MR418M restoration
« Reply #653 on: September 16, 2019, 10:53:51 PM »
It's been another long day.  I'm going to hit the hay and start again in the morning.  Ken, I have a VCR I can use if I can actually get a raster.  I'm not going anywhere with just a white screen and no audio.  My ultimate goal is to find a B&K Analyzer, either a 1076 or a 1077.  My understanding is they are simple to use and effective for TV repair.  I have nothing now in the way of TV testing equipment or signal generators for TV.  I'm guessing that if I get this one going, it won't be my last TV project.  The problem with finding an Analyzer is that shipping is worth more than the device. 
I don't need Google.  My wife says she knows everything.

electra225

  • Hero Member
  • *****
  • Posts: 3749
    • View Profile
Re: Magnavox Stereo Theater 1MR418M restoration
« Reply #654 on: September 17, 2019, 09:19:01 AM »
I'm in the market for a new camera.  I suppose cameras are now obsolete and I need to use my phone.  This one has been good for several years, but it's been dropped and knocked around too much.  The batteries won't stay in without duct tape.  But, as they say, a picture, even a fuzzy picture, speaks louder than words..... ::) ;) :)

The black bar in the TV screen is not there in real life.  That is some kind of reaction between the sweep in the TV and my camera.  See that cute little channel indicator in the corner of the picture tube mask?  I think that thing is neat.  I also like my new wattmeter.  I don't know how I ever got along without one.
I don't need Google.  My wife says she knows everything.

19and41

  • Hero Member
  • *****
  • Posts: 654
    • View Profile
Re: Magnavox Stereo Theater 1MR418M restoration
« Reply #655 on: September 17, 2019, 09:52:45 AM »
That pic looks like the alignments are off.  I would imagine you could get an image with a good video source.
"Any sufficiently advanced technology is indistinguishable from magic."
— Arthur C. Clarke

electra225

  • Hero Member
  • *****
  • Posts: 3749
    • View Profile
Re: Magnavox Stereo Theater 1MR418M restoration
« Reply #656 on: September 17, 2019, 01:34:51 PM »
Which alignments do you believe would be off?  The "squigglies" kind of swim back and forth headed toward the right of the screen.  Do you mean "adjustments" rather than "alignments"?  Adjustments I might be able to do.  I'll need more equipment and knowledge than I have now to do an alignment.  The hum in the audio may have been self-inflicted.  I tied the power cord, wires from the tuner and the audio cable from the TV all in a neat bundle with wire ties.  Perhaps making those wires messy again will cure the hum in the TV audio.
I don't need Google.  My wife says she knows everything.

Bill

  • Hero Member
  • *****
  • Posts: 1686
    • View Profile
Re: Magnavox Stereo Theater 1MR418M restoration
« Reply #657 on: September 17, 2019, 06:52:20 PM »
A picture, or snow, or what every you want to call it is outstanding.  It even fills the whole screen.  :) :)   Did you separate the wires yet to see if the hum goes away?  I think I would try a VCR just for the heck of it.  It might surprise you with a real picture.   ;D ;D

Bill


electra225

  • Hero Member
  • *****
  • Posts: 3749
    • View Profile
Re: Magnavox Stereo Theater 1MR418M restoration
« Reply #658 on: September 17, 2019, 09:02:44 PM »
It surprised me by having a totally dark picture tube!   >:( ??? ::) :-[ :-\

Both the vertical and horizontal are unstable.  I have no audio.  I DID have a raster, but no picture.  Now no raster.  The controls don't seem to want to do much.  The brightness control never has had much affect, but this chassis has Magnalux that controls brightness.  The upper controls, horiz., vert., brightness, and contrast were fairly dirty and scratchy.  I was dinking with them, when the picture flashed a couple times then went dark.  It flashed a couple more times, then nothing.  The wattage is the same, it did not go up or down.  I can hear the vertical oscillator running.  The high voltage never has made any noise.  No tubes are red plating.  I reckon I need to see if I have high voltage.  This thing is going to fight me to the bitter end.  I didn't notice whether the filament in the picture tube was still lit or not. 
I don't need Google.  My wife says she knows everything.

ed from Baltimore

  • Sr. Member
  • ****
  • Posts: 483
    • View Profile
Re: Magnavox Stereo Theater 1MR418M restoration
« Reply #659 on: September 17, 2019, 09:27:12 PM »
             Those squiggles in the picture are probably due to the horizontal and vertical oscillators free-running since with no TV stations tuned in there are no video sync pulses to synchronize to. Having a nice bright raster is great because now you know that all your power supply and sweep section repairs were successful and in addition it means that the horizontal oscillator is free-running very close to the right frequency. If you turn the horizontal hold control a little CW or CCW, you should see the brightness go up and down like peaking a tuned circuit. That dark bar in the picture is probably from the camera shutter catching the picture in the middle of a vertical scan. 
              If you have a VCR or a DVD player with a video output you might inject its video onto the control grid of the 6BL8 (?) video amplifier of the TV chassis and your screen should have a picture on it. ( O Happy Moment !! )  That test will bypass your RF tuner and all 3 of the video IF stages, but you will at least know that the contrast control and wiring around the CRT socket is good.
           I think you have the right idea cleaning up the craziness of the wiring in that beast but don't lace things too tightly or permanently because you may wind up separating certain wires later--especially heavy current filament wiring from audio cables. I actually saw an article talking about the advantages of "sloppy" wiring, it was officially titled "rats nest" wiring. It was used in modules that were to be potted which was good because no-one had to see it.