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Thread: PET 4016 power in from transformer to Jumper 8

  1. #71
    Join Date
    Jun 2012
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    UK - Worcester
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    3,553

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    >>> Took you guys long enough

    More about education Mike !

    Dave

  2. #72

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    Quote Originally Posted by Dwight Elvey View Post
    When you look at the second plot of the ripple, the first thing to notice is that the peak to peak is about 600 mv. Again, it is important to note the frequency. 60 Hz on a full wave rectification indicates an open diode.The next thing to notice is the tight shape of the wave. On the up swing, we are seeing the line following the input sine
    wave. Just after the peak we see the shape break away form the sine path to a relatively constant slop until the sine wave peak catches up to it.
    Now, looking at the first picture. Notice the shape is kind of following the sine wave but is clipping on something on the up sing. This is likely the regulators getting enough voltage to start conducting. Notice that the wave form goes almost all the way to zero. We are probably seeing the tiny effect of the 1 uF caps on the inputs to the regulators, keeping it from going all the way to zero. Even a shorted +5V would not track all the way down to zero as the regulators would stop conducting earlier. To be a load problem it would likely nee to be before the regulators, on the raw DC side. Since you were not complaining about a hot transformer, that leaves only a capacitive failure. As a dry capacitor would cause this wave form.
    Thanks, Dwight. Very clear explanation.

  3. #73
    Join Date
    Feb 2009
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    Southern California, USA
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    2,821

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    Dokken,
    You did a good job on your computer.

    I have a few questions. Was there no goo leaking out of the old capacitor? Or did capacitor dry out as Dwight mentioned? Is the replacement capacitor about the same size as the original? How did you attach it to the chassis?

  4. #74

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    Quote Originally Posted by dave_m View Post
    Dokken,
    You did a good job on your computer.

    I have a few questions. Was there no goo leaking out of the old capacitor? Or did capacitor dry out as Dwight mentioned? Is the replacement capacitor about the same size as the original? How did you attach it to the chassis?
    No leaks, no bulging. So I'm assuming it dried out. The replacement is similar in size and I zip tied it to the chassis using zip ties iike the original.

  5. #75
    Join Date
    Feb 2009
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    OK, thanks to the forum team I learned something about power supplies from this problem. With no goo, I would have replaced the diode bridge and wasted time and effort with that first.

  6. #76
    Join Date
    Dec 2005
    Location
    Toronto ON Canada
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    7,291

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    Quote Originally Posted by dave_m View Post
    OK, thanks to the forum team I learned something about power supplies from this problem. With no goo, I would have replaced the diode bridge and wasted time and effort with that first.
    Yeah, excellent 'Linear Supplies 101' from Dwight.

    Maybe just my own experience but unlike modern small caps I've never seen goo coming out of one of those huge old large-value caps but I have seen them partially or completely open internally (just had a PET with that issue as a matter of fact). Checking ripple with multimeter on DC line but set to AC volts both with and without load can be a simple but revealing test, as can checking ripple frequency as Dwight suggested.

  7. #77
    Join Date
    Feb 2009
    Location
    Southern California, USA
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    Yes, ripple tests will go on my checklist.

  8. #78

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    I just opened the 4040 drive case for the first time. Two more of those 23k uf caps. ughhh.

    I have a broken drive door latch. Any pointers to parts to search for such as brand of OE drive? or I can probably repair this one, but just curious.

    z pet drive door Screen Shot 2020-02-24 at 4.02.16 PM.jpg

  9. #79

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    I used a brass rod and some super glue/baking soda and the door works great.

    a pet door 1 Screen Shot 2020-02-26 at 4.18.04 PM.png

    a pet door 2 Screen Shot 2020-02-26 at 4.18.48 PM.png

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