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Thread: TV Typewriter replica project back on track

  1. #351
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    Ahhh. And now looking at the schematic, it makes sense. And that seems to jive with the schematic:

    psuschematic.jpg

    And indeed on this original TVT with same transformer, that seems to be what was done.

    transformerwiring-tally.jpg

    OK. So much reading/learning to do. But I will try to set up for the tests you recommended and check all this. Just have to get over my fear of live AC power.

  2. #352
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    Quote Originally Posted by falter View Post
    ... it seems to me if I've got 2 6v and 2 12v 'inputs' on the board, and 2 6v and 2 12v outputs form the secondaries, if I connect one 6v to one 6v, one 12v to one 12, another 6v to the other 6v and another 12v to the other 12v.. that would be 'aiding', right?
    No, that would be neither adding nor bucking, that would be connecting them in parallel.

    Only two wires on the transformer should be connected together, leaving you with 5 connections (plus the 110V primary).

    It might help if you listed the colours of the various wires (if you already did and I missed it, what's the post#?); transformers often used a more or less standard colour code.

    m

  3. #353
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    Thanks Mike. This transformer doesn't have any wires... just metal posts that they've labelled with voltages.

  4. #354

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    D5 and D6 are (still?) drawn the wrong way around in you circuit diagram... The capacitor for -12V will go boom...

  5. #355
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    Quote Originally Posted by falter View Post
    Thanks Mike. This transformer doesn't have any wires... just metal posts that they've labelled with voltages.
    Even better. I assume that there are 8 or 9 posts in total; how are they labelled?

    m

  6. #356
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    Even better. I assume that there are 8 or 9 posts in total; how are they labelled?
    Here's what I have:

    20171212_145548.jpg 20171212_145600.jpg

    Now this unit has been out of production for years.. Signal did this as a one off custom job for me. So I'm somewhat confident they labelled it correctly. Looking at my photo of an original TVT above, it does appear to me to line up. You can see the wire on what should be the top 12v post, and then a short wire going downwards diagonally to 0, which seems to be what the schematic and Chuck were saying should be. I hate that I can't make out the other wires.

    And I apologize they come out upside down. The forum software just does that. No idea why.

  7. #357
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    D5 and D6 are (still?) drawn the wrong way around in you circuit diagram... The capacitor for -12V will go boom...
    Per the 'errata' - Diode 6 is backwards on the parts overlay, and the negative supply diodes are backwards on the schematic. I assume that means the overlay is correct. The schematic is riddled with errors, which doesn't help us newbies any! But supposedly the overlays (except for D6) and PCBs themselves were known to be correct.

    Here's the overlay. Note the correction the owner made to change the diode. I followed this overlay in installing my diodes.

    Attachment 42441

  8. #358
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    That diagonal from 0 to 12 (which should be the ground on the board) sounds correct, but do a test with real AC and an AC voltmeter just to be sure. It's worth the peace of mind.

  9. #359
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    Yup, connecting a 0V to the other 12V sounds right. With one probe on the other 0V you should measure the following (somewhat higher since there's no load):

    A0: 0
    A6: 6
    A12 & B0: 12
    B6: 18
    B12: 24

    If that works out then as Chuck says, on the board the junction of A0 and B12 will be ground which then corresponds to the schematic:
    A0: 12V
    A6: 6V
    A12/B0: GND
    B6: 6V
    B12: 12V

    It's usually a good idea to check power supply wiring and voltages before any other parts are installed; can you easily get it back to an unpopulated board (i.e. no semiconductors or electrolytic caps) to make sure the right voltages appear in the right places? The errors around the power supply diodes certainly confuse the issue...

    BTW, the attachment doesn't work for me.

    m

  10. #360
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    Right now the transformer is not connected to anything. I'm wondering though if I could connect it to the AC input from the TVT, just so there's a fuse and power switch? I'd hate to have to desolder the line cord etc again.

    So when you say 'A0:12v' or 'A6:6v', that means literally a wire going from that post to the appropriate point on the mainboard, right? I will attempt the tests first, but just want to make sure I understand what's going on down the road.

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