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GE radio 7-4135

Discussion in 'Troubleshooting and Repair' started by spythe2, Nov 7, 2018.

  1. spythe2

    spythe2

    4
    0
    Nov 7, 2018
    Hello
    I just discovered your site,while looking for some info about the mentioned radio,that has lots of sentimental value to a good friend of mine,so I decided to spend some time to fix it for him.
    My first examination of the radio which is dead,I found out the power transformer has an open primary and 2 burned out resistor R44 AND R45,so I would like to know if I can find a schematic for it and any possible site to buy parts from.Any help will be greatly appreciated.
    By the way I am in Greece and parts for such old radios are hard to find.
    Thank you for your time and for any help you can give me.Spyros
     
  2. Ylli

    Ylli

    200
    37
    Jun 19, 2018
  3. kellys_eye

    kellys_eye

    4,284
    1,145
    Jun 25, 2010
    Is this the genuine model or the reproduction with a cassette player in it?
     
  4. 73's de Edd

    73's de Edd

    2,678
    1,085
    Aug 21, 2015
    A reproduction . . .the old original GE certainly would not have used a modern 7-4135 identifier.
     
    Richard9025 likes this.
  5. spythe2

    spythe2

    4
    0
    Nov 7, 2018
    Hello Ylli
    Thank you for taking the time to answer my post,but I still think we need the schematic in order to determine roughly the output voltage of the transformer going to the rectifier,then see what is the voltage feeding the PCB and besides I have 2 burned out resistors and I cant determine their value,since their bands are smoked. I am sure there is a schematic somewhere out there,so I hope someone will be able to shed some light in to this problem.Again I thank you for answering my post.
    Spyros
    ps by the way what state are you in? for many years I was in the Mile high state,but now I am at sea level(Greece that is)
     
  6. Ylli

    Ylli

    200
    37
    Jun 19, 2018
    I searched for quite a bit and was unable to find a schematic or even any other interior pictures. Perhaps someone will have more luck than I did. I'm in SE Wisconsin, about 800 feet ASL.
     
  7. spythe2

    spythe2

    4
    0
    Nov 7, 2018
     
  8. 73's de Edd

    73's de Edd

    2,678
    1,085
    Aug 21, 2015
    Sir spythe2 . . . . .

    BEHOLD . . .it's a MIRACLE !
    Submitted herewith is your units schematic . . .

    The rest of the story . . . .

    It was retrieved from my inherited massive technical documents collection of paaaaased brother in law ***.
    I had written down your model number on a Post-it and checked it out, the last time out to the mule barns adjunct printed technical
    documentation archival storage area.
    It seems like Gently Electrified and Richard Carlton Astorbilt were living at the same address and sharing the same bed at this time in their past technical history, with their shared techdoc branch being in "Indian" poles . . . . Indiannapolis Indiana.
    So I pulled your units info to be Pee Dee Eff'd and spot checked and additionally I sprayed for silverfish . . . . . as they are paper documents worst enemies, along with mold and decay.

    ***
    I was ALWAYS being hit with the hardest of the hardest of the impossibles, that always accompanied him on their 4 or so annual holiday week end visits . . . if not, his making dedicated special trips..

    SCHEMATIC . . . . .of power supply . . . .

    Now in initial viewing of that section you need to see if your unit had the optional 220 power input and its tell tale crossover switch of 120 - 220 .
    I didn't even realize that they had favored any overseas marketing at that time.
    You will immediately know if you have one of those foreign market models . . . . by that switches presence .
    Otherwise you will be having the top schematic for T101.
    With the A.C.cord set that properly mates up with P1-P2.
    (Whereas, the bottom transformer would have used the A.C.cord set that properly mated up with P3-P4 )

    You also can see that this is using a power transformer, being wound with a high impedance / low core loss primary winding, since it is being
    plugged directly into the AC line 25 hrs a day. The power switch is located in the power supply secondary circuitry, and switches raw DC into the regulated supplies.

    What happened . . . .?

    Either some DERN FEWL . . . plugged it into 220VAC . . . . or . . . .

    One might initially suspect a very -very nearby lightning hit to the AC line / sub transformer, possibly of such a duration to open the primary primary transformer winding.
    A failure analysis teardown evaluation should reveal a round copper ball upon one or both of the opened copper winding wire junctions.
    If a surge voltage burst did happen to initially make it thru the transformer primary and into the secondary there is the voltage reduction plus having to initially pass thru line inductors L6-7.
    They are as effective against initial line spikes and micro voltage surges as a hairpin curve is to a Mercedes 300SL coming down into it at 140mph.
    Then you have to figure in the caps C46-7-8-9 that can short down or D1-2-3-4 diodes as well.
    AND THEN . . . . you have found one of the R45-44-20, 6.8 ohm 1/2 w, series arranged resistors being open.
    You can suspect that being due to a dead shorted D5 Zener diode.
    If you want to preclude any zener problems in the future, build in the PINK circuit, drawn in to the .right, to upgrade to make the unit using an amplified POWER zener.

    THE TRANSFORMER . . . . .
    If my problem to solve, I would be very-very GENTLY peeling back the covering of the transformers made connections from the plastic main lead wires into the enamelled, soldered on, ~32--38 ga tinned wire endings, of the transformers primary winding.
    Initially, I would want to see if only two heavier plastic leads and their mating, soldered on enamelled and tinned copper wires are solely involved, OR if a thermal fuse is ALSO being incorporated, installed internally down inside, near the metal laminations , to take a temp sampling.
    That then gives a second connection set, so you would find 3 wire connections being involved with the primary connections, BUT only two larger plastic wires coming out to connect to AC...

    If you find that the transformer has to be replaced . . .seems like a 12VAC secondary on your proper line voltage primary should rectify and filter out, right at your needed DC supply voltage needed and a 1 amp secondary current rating should be more than adequate for this units needs.

    Le Schematique . . . . .

    [​IMG]



    73's de Edd . . . . .
    . . . . . . . . . . .


    I used to eat a lot of natural foods . . . . until I heard that most people die of natural causes !
     
    Last edited: Dec 22, 2018
    Richard9025 likes this.
  9. spythe2

    spythe2

    4
    0
    Nov 7, 2018
    Dear 73's de Edd
    Indeed its a miracle to have the schematic you sent me and I really dont know how to thank you,as I had the radio taken apart and since I was not able to find any info on it,My dear friend who I was going to fix the radio for asked me to put it together,as he was going to have it just for looks,so now your "miracle" schematic has revived my interest in fixing the radio for my dear friend. FYI the radio model PB7-4135 was made for 110/220 volt having the proper transformer and sw. to select the proper line voltage.When I opened the radio I saw the smoked resistors R44 and R45 and checking the transformer I found an open primary(no resistance between the black and brown wires),but had continuity between the orange and brown,indicating it was ok for 110 volt,but not 220v.The radio had an American plug with perhaps an adapter to European round prongs plug.I will ask my friend,if he wants me to get back the radio,search for a 220/12vac, 2 resistors 6.8 ohms and perhaps the zener 11v diode as well and hopefully,I will not need addional parts to put it in a working order.I will also spend some time to investigate the transformer as you suggested, to find out what caused all this mess. I personally think it was a poor design,not to incorporate any kind of safety,like a fuse ,or to switch the primary voltage to eliminate the wasted power,being on all the time.I will of course keep you posted on the progress,should my friend give me the ok to fix for him.
    Again I would like to thank you so much for your time,and to wish you Happy Holidays and may the new year bring you, anything you might desire and of course good health and time to help more people.For more than 25 years I worked for one of the biggest Natural Gas/OIL companies in Texas(COASTAL/EL PASO) so I like to say "you all be good now you hear"
     
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