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Thread: PET 4016 power in from transformer to Jumper 8

  1. #21

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    Quote Originally Posted by Dokken View Post
    Dwight, thank you so much for your reply. most of this will require some research or advice on how to achieve these measurement with the scope. i will study it.
    First thing to look at is the ripple frequency. If it is 60Hz, you have one bad diode. For ESR, you can look at the shape of the signal after the peak. There will be a curve on the up side and it will go over the peak. If after the peak, if follows a curved path before separating into a straighter discharge line, you'd know that it had poor ESR. If the voltage came up to about 11 or 12 volts and dropped to less than 6 volts between peaks, it would either mean the capacitance was really low ( dry inside ). If the voltage never makes it to 11 or so volts it might mean the load was too heavy.
    Dwight

  2. #22

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    Quote Originally Posted by Dwight Elvey View Post
    First thing to look at is the ripple frequency. If it is 60Hz, you have one bad diode. For ESR, you can look at the shape of the signal after the peak. There will be a curve on the up side and it will go over the peak. If after the peak, if follows a curved path before separating into a straighter discharge line, you'd know that it had poor ESR. If the voltage came up to about 11 or 12 volts and dropped to less than 6 volts between peaks, it would either mean the capacitance was really low ( dry inside ). If the voltage never makes it to 11 or so volts it might mean the load was too heavy.
    Dwight
    thank you! and a likely silly question, i can probe at any of the regulated outputs from the regulator section, such as the +3.7 that should be +5?

    edit: after thinking about this, i should be probing the unregulated side?
    Last edited by Dokken; February 19th, 2020 at 02:35 PM.

  3. #23
    Join Date
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    Quote Originally Posted by Dokken View Post

    connector from transformer to J8:
    1 2 3 4 5 6 7 8 9
    brn red blk red brn blk key blue blue

    2 and 4 go through the filter capacitor.

    what i measure:
    1 to 5 = 18 vac
    8 to 9 = 17 vac
    On my Pet with J8 cable not connected to main board (diode bridges), I get 22 VAC between J8- pin 1 to 5. You get 18 VAC. That is not much head room to develop the +/- 9 V unregulated from bridge circuit.
    Also when J8 cable is connected to the board, you are reporting +7.5 VDC and -11 VDC unregulated instead of +/- 9 VDC. It should be balanced as the center tap (black wire) should be connected to J8 -pin 3 which is grounded to J8-pin6. Make sure the center tap connections are good.

  4. #24

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    thanks. i re-read the transformer voltages and mapped them out. these readings are while nothing is connected to the main board. monitor power from transformer remains connected (pins 11/9).


    transformer photo:
    https://imgur.com/G2tyIqW

    transformer voltage readings:
    https://imgur.com/jlzOtRG

    thoughts?

  5. #25

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    for kicks, i pulled one of the monitor power wires from the transformer and re-read voltages. a few readings increased, notably 9-5 from 8v to 14v, 7-4 from 2.4 to 5.2, 8-6 from 4.8 to 7.8.

    could this be normal? or is there possibly something shorted in the monitor section?

    xformer voltages without motherboard or monitor power connected (in RED):
    https://imgur.com/NOneS3B

  6. #26

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    and the readings on the transformer schematic.

    https://imgur.com/D9gtkXi
    Last edited by Dokken; February 20th, 2020 at 05:18 AM.

  7. #27

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    Quote Originally Posted by Dokken View Post
    for kicks, i pulled one of the monitor power wires from the transformer and re-read voltages. a few readings increased, notably 9-5 from 8v to 14v, 7-4 from 2.4 to 5.2, 8-6 from 4.8 to 7.8.

    could this be normal? or is there possibly something shorted in the monitor section?

    xformer voltages without motherboard or monitor power connected (in RED):
    https://imgur.com/NOneS3B
    Most of these reading are useless noise. With no loads and using a high impedance meter, most of these number are just capacitive coupling of the windings.
    First thing to do is check to see which wires share the same winding. Disconnect the connector and with the power off measure the secondary windings with an ohm meter. The secondary winding should be less than 10 ohms. Note anything that looks wrong. The connector pins 8 to 9 should be less than 10 ohms. Pin 8 to to pin 1 should be open. Pins 1, 3 and 5 should be less than 10 ohms.
    With the connector disconnected from the loads and powered up measure the voltage from connector pins 1 to 5. The reading you show looks wrong in the next post.
    Dwight

  8. #28
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    Feb 2009
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    Southern California, USA
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    Dwight,
    Here is the pinouts of the PET transformer.

    PET Transformer2.jpg

  9. #29

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    Quote Originally Posted by Dwight Elvey View Post
    The connector pins 8 to 9 should be less than 10 ohms. Pin 8 to to pin 1 should be open. Pins 1, 3 and 5 should be less than 10 ohms.
    With the connector disconnected from the loads and powered up measure the voltage from connector pins 1 to 5. The reading you show looks wrong in the next post.
    Dwight
    i'm getting 0.4 ohms on 8/9, 1/3/5.

    voltage 1 to 5 is 18.4.

  10. #30
    Join Date
    Jun 2012
    Location
    UK - Worcester
    Posts
    3,790

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    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
    Last edited by daver2; February 20th, 2020 at 12:21 PM.

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