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Cromemco System One Update (was 1uF 50v...)

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  • billdeg
    I need to spend more time with the Tektronix 5103N I picked up at VCF to be sure whether or not there is a ripple coming into the LAS1412. I am going to read
    Message 1 of 33 , May 29, 2014
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      I need to spend more time with the Tektronix 5103N I picked up at VCF to be sure whether or not there is a ripple coming into the LAS1412.  I am going to read up on this tonight.

      First of all, there is an LED that indicates when +12V is OK.  When I disconnect the 12V feed to the diskdrives the light comes on, but further testing shows it will light under voltage.  There is ~20V coming into the LAS1412, +11.52v coming out.  This value carries through to what should be the 12V line that feeds the disk drives.  The drive is not the problem after all.  To verify this I put in a separate 12v/5v power supply to power the drives and I can boot the system successfully.

      As far as I can tell from the schematic there is a 16v line coming in to the LAS1412, 12V coming out.  On the way to the 12V feed for the disk drive is a 590uF 20v cap and a 1uF 50v cap.

      Measureing the output of the LAS1412 is 11.52v. 
      The 1uF 50v reads 11.52. 
      The 590uF 20v reads 11.52v. 
      The output to the 12v line is 11.52. 
      Basically it's 11.52 wherever you can measure it.

      When I replaced the LAS1412 there was no voltage at the 12V so I at least improved the situation I suppose.

      At 11.52v the drive can almost boot but there is not quite enough power.


      Thanks for your interest. 


      Bill

    • Dan Roganti
      ​The junior engineer comes in to talk to his boss, the seasoned engineer. I m having trouble with that power supply circuit you put me to work on. says the
      Message 33 of 33 , May 30, 2014
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        ​The junior engineer comes in to talk to his boss, the seasoned engineer.
        "I'm having trouble with that power supply circuit you put me to work on." says the junior engineer
        "OK, let's talk about it, Is it oscillating?", asked the seasoned engineer
        "No, it's stable", says the junior engineer.
        "How is the efficiency?",asked the seasoned engineer
        "About 87%", says the junior engineer.
        "Is there ringing on the gate?", asked the seasoned engineer
        "Nothing above normal", says the junior engineer.
        "What about noise and ripple?", asked the seasoned engineer
        "They are well within spec", says the junior engineer.
        "Then what's the problem ??", asked the seasoned engineer
        "The darn thing's on fire !!!"​
        ​ , says the junior engineer.​


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