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Thread: PET 4016 power in from transformer to Jumper 8

  1. #31

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    The schematic on Zimmers shows different pins on connector 8. I'm using the schematic that ( I think it was ) Dave_m posted.
    It shows the center tap going to pin 4 and not pin 3.
    See http://www.zimmers.net/anonftp/pub/c...8032087-11.gif
    Note when we were talking about a floating center tap?
    Dwight

  2. #32

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    Quote Originally Posted by daver2 View Post
    What about the voltage reading from 1-3 and from 3-5?

    Again, 18.4 Volts from 1-5 looks a little bit low?

    Unfortunately, I had a tidy up over Christmas, and a key piece of paper (the transformer voltage readings from my system) have been stored away safely...

    Dave
    Thanks for your input on my dilemma!

    1-3 =9.2, 3-5 = 9.2, 1-5 = 18.4.

  3. #33
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    >>> It shows the center tap going to pin 4 and not pin 3.

    Which takes me back to my post #2 where something 'needled' me about pin 4...

    I need to find my bit of paper that had all of this on...

    I think pin s3 and pin 4 are swapped in some diagrams - either that or some PETs used pin 4 for the centre tap and others used pin 3...

    >>> 1-3 =9.2, 3-5 = 9.2, 1-5 = 18.4.

    So, you have Volts there - and both halves of the winding look OK.

    Dave

  4. #34
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    I have just had a look at my PET.

    The centre tap goes to pin 3 on J8.

    Pin 4 on J8 has a red wire which goes to the capacitor positive terminal (as does J8 pin 2).

    Pins 1 and 5 on J8 should have brown wires - these are the two ends of the double winding; and pin 3 of J8 should have a black wire - which is the centre tap.

    J8 pin 4 is the positive output from the bridge rectifier 'going to' the capacitor which then 'comes back in' on J8 pin 2 to the +5V regulator.

    It's getting a bit late in the UK, so I will measure my transformer voltages tomorrow - but Dave has posted his and your ac voltages look a little bit low when compared to his (18.4 Volts on yours and 22 Volts on his).

    Dave

  5. #35
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    Quote Originally Posted by Dwight Elvey View Post
    The schematic on Zimmers shows different pins on connector 8. I'm using the schematic that ( I think it was ) Dave_m posted.
    It shows the center tap going to pin 4 and not pin 3.
    See http://www.zimmers.net/anonftp/pub/c...8032087-11.gif
    Note when we were talking about a floating center tap?
    No, The center tap from the transformer is a black wire and goes to the negative terminal on the big C1 capacitor. From there, two black wires go to J8 pins 3 and 6. Both are grounded on the mainboard.

    J8 pins 2 and 4 are red wires that go to the positive terminal of C1, The voltage there is the unregulated +9 VDC.

    -Dave

  6. #36
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    Here is power supply circuit diagram.

    PET PS copy.jpg

  7. #37

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    Hi Dave_m
    Thanks for the clarification. The wiring makes sense now. I didn't look at the way they'd used the diode bridge.
    Dwight

  8. #38

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    xformersmall Webp.net-resizeimage.png

    for reference, my readings (the image size restrictions on this forum are harsh).

    so, where should i go next with this?

  9. #39
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    Please tell me you haven't got 17.2 Volts across J8 pins 2 and 6 though!!!

    Ah, found my paperwork! I had put it somewhere safe after all!

    I read approximately 8V AC from the centre tap (black wire) to each of the brown wires; and approximately 16.3V AC between the two brown wires. So I read less than yours (with no load).

    It's all coming back to me now! J8 pin 4 is missing from the schematic in post #39 - which is why it is difficult to see how things work when you marry up the transformer/capacitor/J8 schematic with the main board regulator schematic. There is a wire missing from the schematic!

    Dave
    Last edited by daver2; February 20th, 2020 at 02:22 PM.

  10. #40

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    Connect things up again and remeasure. Make sure when doing DC measurements that the meter is set to DC.
    Those reading that you have look correct.
    Dwight

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