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Saturday, January 29, 2011

VOXSON Mod. 1202 CHASSIS 4-55-19270 INTERNAL VIEW.

















This VOXSON Mod. 1202 CHASSIS is amazing.

Power supply is realized with an AD142 which is a germanium Transistor.


The tuning circuits has a large knob potentiometers tuning system which use voltage controlled capacitances such as varactor diodes as the frequency determining elements.

Therefore a stable AFC circuit is developed:

A superheterodyne receiver having an automatic intermediate frequency control circuit with means to prevent the faulty regulation thereof. The receiver has means for receiving a radio frequency signal and mixing the same with the output of a superheterodyne oscillator. This produces an intermediate frequency signal which is coupled to a frequency or phase discriminator to produce an error signal for controlling the frequency of the superheterodyne oscillator. A regulation circuit is provided having an electronic switch to interrupt the feedback circuit when only unwanted frequencies tend to produce faulty regulation of the superheterodyne oscillator.









Power supply is realized with mains transformer and Linear transistorized power supply stabilizer, A DC power supply apparatus includes a rectifier circuit which rectifies an input commercial AC voltage. The rectifier output voltage is smoothed in a smoothing capacitor. Voltage stabilization is provided in the stabilizing circuits by the use of Zener diode circuits to provide biasing to control the collector-emitter paths of respective transistors.A linear regulator circuit according to an embodiment of the present invention has an input node receiving an unregulated voltage and an output node providing a regulated voltage. The linear regulator circuit includes a voltage regulator, a bias circuit, and a current control device.

In one embodiment, the current control device is implemented as an NPN bipolar junction transistor (BJT) having a collector electrode forming the input node of the linear regulator circuit, an emitter electrode coupled to the input of the voltage regulator, and a base electrode coupled to the second terminal of the bias circuit. A first capacitor may be coupled between the input and reference terminals of the voltage regulator and a second capacitor may be coupled between the output and reference terminals of the voltage regulator. The voltage regulator may be implemented as known to those skilled in the art, such as an LDO or non-LDO 3-terminal regulator or the like.
The bias circuit may include a bias device and a current source. The bias device has a first terminal coupled to the output terminal of the voltage regulator and a second terminal coupled to the control electrode of the current control device. The current source has an input coupled to the first current electrode of the current control device and an output coupled to the second terminal of the bias device. A capacitor may be coupled between the first and second terminals of the bias device.
In the bias device and current source embodiment, the bias device may be implemented as a Zener diode, one or more diodes coupled in series, at least one light emitting diode, or any other bias device which develops sufficient voltage while receiving current from the current source. The current source may be implemented with a PNP BJT having its collector electrode coupled to the second terminal of the bias device, at least one first resistor having a first end coupled to the emitter electrode of the PNP BJT and a second end, a Zener diode and a second resistor. The Zener diode has an anode coupled to the base electrode of the PNP BJT and a cathode coupled to the second end of the first resistor. The second resistor has a first end coupled to the anode of the Zener diode and a second end coupled to the reference terminal of the voltage regulator. A second Zener diode may be included having an anode coupled to the cathode of the first Zener diode and a cathode coupled to the first current electrode of the current control device.
A circuit is disclosed for improving operation of a linear regulator, having an input terminal, an output terminal, and a reference terminal. The circuit includes an input node, a transistor, a bias circuit, and first and second capacitors. The transistor has a first current electrode coupled to the input node, a second current electrode for coupling to the input terminal of the linear regulator, and a control electrode. The bias circuit has a first terminal for coupling to the output terminal of the linear regulator and a second terminal coupled to the control electrode of the transistor. The first capacitor is for coupling between the input and reference terminals of the linear regulator, and the second capacitor is for coupling between the output and reference terminals of the linear regulator. The bias circuit develops a voltage sufficient to drive the control terminal of the transistor and to operate the linear regulator. The bias circuit may be a battery, a bias device and a current source, a floating power supply, a charge pump, or any combination thereof. The transistor may be implemented as a BJT or FET or any other suitable current controlled device.


- The EHT Output is realized with a selenium rectifier.

The EHT selenium rectifier which is a Specially designed selenium rectifiers were once widely used as EHT rectifiers in television sets and photocopiers. A layer of selenium was applied to a sheet of soft iron foil, and thousands of tiny discs (typically 2mm diameter) were punched out of this and assembled as "stacks" inside ceramic tubes. Rectifiers capable of supplying tens of thousands of volts could be made this way. Their internal resistance was extremely high, but most EHT applications only required a few hundred microamps at most, so this was not normally an issue. With the development of inexpensive high voltage silicon rectifiers, this technology has fallen into disuse.A selenium rectifier is a type of metal rectifier, invented in 1933. They were used to replace vacuum tube rectifiers in power supplies for electronic equipment, and in high current battery charger applications.

The photoelectric and rectifying properties of selenium were observed by C. E. Fitts around 1886 but practical rectifier devices were not manufactured routinely until the 1930s. Compared with the earlier copper oxide rectifier, the selenium cell could withstand higher voltage but at a lower current capacity per unit area.

18 comments:

  1. Hi Frank!

    I have exactly the same TV, but it doesn't work. I took it to a video specialist to have it repaired, but the guy sad that in order to fix it he would need a wiring diagram. I don't have anything like that and had no luck on google either.
    Do you still have the manual or any technical documents for this TV? I am glad for anything helpful!

    Regards,
    Sarah

    ReplyDelete
  2. Sarah,

    On top of all, one First thing:
    what's wrong with the tellye ?

    This is important !


    Second, a skilled TV Engineer technician doesn't need the schematic for such relatively simple TV chassis !

    ReplyDelete
  3. Hi Frank,

    the technician said that the the line synchronization is corrupt (it has slipped ? - I don't really know how to explain this correctly, because English is not my native language and I have very little knowledge of all the technical terms).
    the sound does work perfectly and the picture tube is undamaged, so I think it should be no big problem to get the tellye working again.

    Thanks for the quick reply,
    Sarah

    ReplyDelete
  4. Hi Sarah,

    Good to read that the telly is at least powering up and running even only with "voice".

    Your technician doesn't say the truth. It uses a incoerent technical language which doesn't reflect any real fault in a Tellye line synchronization stage circuit.

    Anyway:

    1 - How did you connect the tellye to test it ?

    This is important because it may be the real problem.

    2 - Did you have at least a picture even only noise (I.E. like running it without antenna should give a sparkly / noise white screen picture ) ?

    (Your english is fine).

    FRANK.

    ReplyDelete
  5. Hi Frank,

    I see on your blogger profile that you are located in Germany, so I will give it a try and try to explain in German :-)

    Ich hatte mir zunächst einen UHF/VHF Modulator gekauft, in den ich über Chinch Anschlüsse ein Signal von meinem Laptop einspeise (das Bildsignal geht vorher nochmal durch einen digital-zu-analog Wandler).
    Von dem Modulator aus geht dann ein Koaxialkabel zum Fernseher, angeschlossen über einen Adapter an die UHF und VHF-Anschlüsse des TVs.
    Ton kam so problemlos an, Bild leider nicht. Allerdings sieht man nicht mehr den Schnee der ganz ohne Signal entsteht, sondern ein graueres, weniger rauschendes Bild was sich auch ändert wenn man an den Kanälen herumstellt.
    Der Techniker hat mein Adapter-Konstrukt dann entfernt und versucht, selbst ein Signal drauf zu bekommen, es kam aber das selbe Ergebnis. Daraufhin sagte er, dass die Zeilensynchronisation "gekippt" sei, womit ich als Laie natürlich wenig anfangen kann. Warum er dafür eine Schaltskizze haben will, ist mir auch nicht ganz klar.

    Soweit die Ausgangslage, ich hoffe ich muss das Gerät nicht zum Deko-objekt degradieren.

    Gruß,
    Sarah

    ReplyDelete
  6. Sarah,

    Ja alles gut aber das "ding" funktioniert nicht richtig oder ?

    Est ist besser im english schreiben, da die ganze welt hier liest.

    OK, Sarah,
    First Try to do some photograph of the screen when the telly is running with a picture on it.
    Then upload it to Imageshack.us
    after that , post here the links with the files, will give a look at them soon.

    (Be aware that photographing running tellyes isn't easy at all, so please do your best regarding this. Remote diagnosing isn't easy ! ! ! )

    Anyway i'm thinking that the video source that you're using isn't liked by the telly which is requiring a standard CCIR PAL signal to work properly and better if tuned in UHF band instead of the VHF band.

    Why you don't try to input a RF signal from a VHS VCR in the same way you did from the laptop, just to test something a different signal source.

    FRANK.

    ReplyDelete
  7. Hi Frank,

    I will do this once I get the tellye back from the technician, in case he can't fix it (I can't tell how likely this is). Right now he has the TV so I can't take a photo of it now.
    Usually I only collect audio devices (turntables, amps and such) and this is the first vintage TV I got.
    Anyhow, I will let you know as soon as I have any news about this.

    Have a nice day,
    Sarah

    ReplyDelete
  8. Hi Frank,

    I got the telly back today and it works. Here are some pictures and the result of the whole project:
    http://twenty-flight-rock.co.uk/2011/12/08/new-and-running-voxson-1202/

    Nevertheless I thank you for the patience you had for me!

    Cheers,
    Sarah

    ReplyDelete
  9. Glad you get it running OK !

    Smart persons like you are getting always successful things !

    FRANK.

    ReplyDelete
  10. Hi Frank!

    I just acquired one of these myself. Unfortunately without a power cable though.

    I have been googling for hours and can’t seem to track down this 4-pronged round power cable.

    Would you by any chance know the name of TVs plus / or cable ?

    Thanks!

    Paul

    ReplyDelete
  11. That's difficult. The name of the Tv is seen a the title of the post : VOXSON Mod. 1202 (yr 1972 ! ! !) The original firm Voxson is defunct many time ago. I will give you a suggestion: 1 - To power up the set just find which of the socket contact goes to the real 220v power supply line from the socket itself to switch. Study it before as the're fuses on the line. 2 - Apply a compatible socket connector relatively obtainable today's. Of course don't expect to fit it like plug & play, eventually a bit of work may be required. If I'm not wrong and my memories aren' tainted much, there was one time some PHILIPS 70's radio cassette recorders socket plug which was easy to "adapt". If you see the distances between the contacts aren't too critical. You can even adapt single female contacts at the male pins at tv socket level. DON'T expect to find original VOXSON's sockets parts........... see it's a 1972 object. Bear in mind that the original socket by design weren't that safe. Just look that on the same connector socket but not line there are both shared a 220V supply and a 12VDC supply. Have, FUN............

    ReplyDelete
  12. Thanks for your help Frank. I fashioned a home-made power cable and managed to power the tv up. See here:

    https://imgur.com/a/3lvtn

    Now I will get myself a composite to VHF/UHF converter to try and feed it a video signal.

    I'm a little concerned about the image not filling the whole height of the screen though. Do you think there might be some damage there ?

    Thanks,

    Paul

    ReplyDelete
    Replies
    1. It Works ! Picture tube seems fine.

      Now what you have is a simple Frame deflection collapse, nothing bad.

      1-It may be a simple mistuning of the Vert Ampl potentiometer in frame/vertical deflection. Adjust it accordingly to cover the entire screen surface *better with a picture or even a tescard picture.

      2-There may be one or more supply in the frame/vertical deflection with lowered values.

      3-There may one or more Aged and dry electrolytic capacitors in frame/vertical stages.

      My guess is that my point 1 will fix quickly the issue.

      Have fun.

      Delete
    2. Thanks for your reply Frank.

      I am once again at my wit's end and was wondering if you might be able to help.

      I got myself an RF modulator so I could try sending a video signal to the TV. It’s the “Konig Mono RF Modulator”:
      http://attachments.content4us.com/datasheets/MAN_SAT-MOD12_COMP.PDF

      I hooked it up over the UHF antenna connection of the TV.

      It has a test signal function enabled by flipping a dip switch. I manage to get sound to come out, but no video, as you can see from the video:

      https://vimeo.com/263546573

      I tried using different channels by playing around with the dip switches on the modulator and trying different buttons and potentiometers on the TV, however it’s nothing but snow!

      Maybe you have an idea of what I’m doing wrong ?

      Thanks,

      Paul

      Delete
    3. It will not work !!!

      1 - You need PAL and not PAL/G !


      2 - You need a VHF/UHF Demixer. You can not apply the RF signal directly in the 300Ohm sockets ! The inputs are separate both VHF and UHF and have 300Ohm impedance ! You need a Demixer for both inputs which brings 75Ohm Mixed to 300+300 Ohm VHF UHF separate signals path !

      As example you can surf Obsolete Technology Tellye Web Museum the old b/w televisions sets, some of these have that what you need, pictured.

      Delete
  13. Hi Frank!

    I’m stuck again. Hopefully with your help one day I will get it! :)

    I got a VHF/UHF matching transformer but still no dice. I can hear the audio from the test signal (that’s the beep in the video below) but no video.

    Here’s a link to a video to illustrate what is happening:

    https://www.dropbox.com/s/syhulajxn1wu86d/IMG_6099.MOV?dl=0

    Thanks for all your help,

    Paul

    ReplyDelete
    Replies
    1. Can`t see the video !

      (I haven`t to join or subscribe any service to watch / download a video like the way, for computers OS, that I haven`t to build a package to install a package....) You get the point ?

      Better upload to youtube and just provide a valid link. It`s easier.



      And to all people like you: STOP using dropbox, google drive , tynipic, photobucket, imageshack , and similar services which are crappy by design !

      NOTE: Why you don`t use a VCR with his RF out and apply it to a valid UHF and VHF Demixer unit ?



      NOW One more question for you:

      Are you sure that the VOXSON Mod. 1202 is fully functional and may not require perhaps a full restoring and checking by a qualified and trained tv engineer ????



      Delete
    2. Here, this link should work: https://vimeo.com/270179466

      You might be right the TV could be damaged.

      I was thinking it might be hard to find an engineer capable of dealing with this older technology, but I might have to do that in the end!

      Delete

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