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Thread: PET 4016 power in from transformer to Jumper 8

  1. #11
    Join Date
    Feb 2009
    Location
    Southern California, USA
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    2,833

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    Quote Originally Posted by Dokken View Post

    Plugged it in, and i get the this on the display.

    https://imgur.com/a/0j5rmwL
    Until you get the correct DC voltages, and verify that the horizontal and vertical drive signals are good at the J7 connector, it would be prudent to disconnect the J7 video connector to the video board to avoid any damage to the video board and CRT.

    The schematics for your computer are here: http://www.zimmers.net/anonftp/pub/c...iv2/index.html

  2. #12
    Join Date
    Jun 2012
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    UK - Worcester
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    Good call about disconnecting the monitor Dave. I forgot that one...

    Would be sensible to post the link configuration for the main board to make sure everything is correct.

    Where did you get this machine from? Just thinking that the previous owner tried to upgrade the PET and failed or whether the machine was built like this (and worked) in the first instance.

    Dave

  3. #13

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    The +5 and -5 are +3.8 and -3.4 regulated. any thoughts on where this variance would originate? they're going through different regulators? and the -11 unregulated coming out of bridge rectifier CR2 should be -5. looks odd.

    voltage schematic with my readings:
    https://imgur.com/BbdXyAa

    this pet came third hand but was originally at a local recycler. no idea of the history.

    I keep the monitor connector disconnected when probing, thanks for that advice. there is a power lead up to the monitor area directly from the transformer, i think. i have not looked in the monitor area yet.

    I do have a scope and will look at the video connector signals as soon as i can.

    thank you both so much for your help. i really hope to get this beauty working.
    Last edited by Dokken; February 19th, 2020 at 02:45 AM.

  4. #14
    Join Date
    Jun 2012
    Location
    UK - Worcester
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    3,565

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    I suppose the obvious question to the voltage deviation is "does your multimeter work correctly"?

    Measure the dc voltages with your oscilloscope to get a comparison.

    >>> thank you both so much for your help. i really hope to get this beauty working.

    People less able than yourself have managed to resurrect machines in much worse condition than yours. Believe me!

    Dave

  5. #15

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    As for the +5V outs, many older regulators required more than 2.5V head room. Not getting 9V where it is expected on the raw DC is an issue. It looks like the filter capacitor is missing or failed. One should use a scope to see what things are doing.
    What kind of current is the load using. Maybe things are just loaded down.
    Dwight
    Last edited by Dwight Elvey; February 19th, 2020 at 05:55 AM.

  6. #16

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    Quote Originally Posted by Dwight Elvey View Post
    As for the +5V outs, many older regulators required more than 2.5V head room. Not getting 9V where it is expected on the raw DC is an issue. It looks like the filter capacitor is missing or failed. One should use a scope to see what things are doing.
    What kind of current is the load using. Maybe things are just loaded down.
    Dwight
    Are you referring to the giant filter cap by the transformer? Any tips on how to test it? I have an ESR meter but it show nothing but I doubt it works on 10k+ mfd parts.

    Thanks, and pardon my inexperience on this.

  7. #17

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    Yep, that would be the one. There is likely a couple of stud mount diodes between it and the transformer on the positive post of the capacitor. This is where a scope comes in handy. You can look at the ripple to see how loaded it is, if both diodes are functioning and the relative amount of ESR it has.
    Dwight

  8. #18

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    i attempted to scope the video pins.

    J7/5 horizontal
    https://imgur.com/MvcePFw

    J7/3 vertical
    https://imgur.com/SID1TZ8

    What does this tell me?

  9. #19

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    Quote Originally Posted by Dwight Elvey View Post
    Yep, that would be the one. There is likely a couple of stud mount diodes between it and the transformer on the positive post of the capacitor. This is where a scope comes in handy. You can look at the ripple to see how loaded it is, if both diodes are functioning and the relative amount of ESR it has.
    Dwight
    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.

  10. #20

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    voltage check update. i was reading the wrong point for the -5 regulated, it seems ok at -4.9.

    The +5 regulated ia still at 3.8.

    https://imgur.com/g7ZyoSj

    edit: i also validated the multimeter voltages with my oscilloscope. very, very close.

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