Need help troubleshooting a micronta power supply

Discussion in 'General Electronics Chat' started by magnetman12003, Jun 7, 2010.

  1. magnetman12003

    Thread Starter Active Member

    May 10, 2008
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    I have an older Micronta adjustable dual-tracking DC power supply Model 22-121.

    I also have the service and circuit manual. Can upload that to anyone interested in helping me figure out where my problem is. I have gone so far but need help to continue.

    Contact me directly at <snip> so I can forward you a copy of the entire sevice manual. I will tell you exactly what my problem is so you can reference it.

    Many thanks, Tom
     
    Last edited by a moderator: Jun 7, 2010
  2. SgtWookie

    Expert

    Jul 17, 2007
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    Tom,
    We don't do things via E-mail here, as that defeats the purpose of the Forums.

    Can you scan the schematic and post it in .png format as an attachment?

    Have you opened the supply?

    I would expect the most likely culprits would be electrolytic capacitors that have dried out.
     
  3. magnetman12003

    Thread Starter Active Member

    May 10, 2008
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  4. Bychon

    Member

    Mar 12, 2010
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    Apparently I don't have any shots per day. The site blocked Firefox AND Internet Explorer from downloading.
     
  5. SgtWookie

    Expert

    Jul 17, 2007
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    OK, so I'll attach it.

    Had no problems using Google's Chrome.
    (I'm going to be changing to Iron soon; same browser without the slow-downs)
     
  6. SgtWookie

    Expert

    Jul 17, 2007
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    So, we now have the manual, schematics, and troubleshooting tips.

    What problems are you experiencing?

    Did you go through the troubleshooting tips?
     
  7. Bychon

    Member

    Mar 12, 2010
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    It's a pair of 723's
     
  8. tracecom

    AAC Fanatic!

    Apr 16, 2010
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    Schematic for reference.
    [​IMG]
     
  9. magnetman12003

    Thread Starter Active Member

    May 10, 2008
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    0
    Hi All,

    I bought this power supply and it had not been used for quite some time. I cleaned it up and it looks like it has never tampered with. I let it operate for 2 days to reform the capacitors. Then I proceeded to check it out.


    Reference service manual pages 6 and 15.

    VOLTAGE
    On page 6 in the "Tracking Alignment" I could only get B output up to 15.18 volts adjusting VR3 to maximum.
    A output is 15.37 volts. MODE SWITCH B TRACKS A - VOLTAGE CONTROLL AT MAXIMUM

    On page 6 under the "Meter Alignment" step 1 and step 3 were completed ok. Thats the voltage. I could adjust the power unit meter to the 15 volt reading on my voltmeter( multimeter).


    CURRENT
    Steps 2 and 4 page 6 is where I am having trouble. No indication on my power unit meter of any current at all when the switch on the power unit front side has Amps selected. Both A and B read zero MODE SWITCH INDEPENDANT - VOLTAGE ADJUSTED TO 15 VOLTS

    However I show on my ( multimeter) Ampmeter while connected to the A terminals a reading of 3.35 amps which can be varied. 0 - 3.35 using the A voltage controll knob

    The same as above applies to the B terminals but a reading of 0-3.70 amps can be varied with the B voltage controll knob.

    Any ideas what is wrong?

    Tom
     
  10. magnetman12003

    Thread Starter Active Member

    May 10, 2008
    31
    0
    Hi All,

    Everything I did is now posted previously so this is a new thread.

    Any suggestions?

    Tom
     
  11. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    show me the thread.
     
  12. SgtWookie

    Expert

    Jul 17, 2007
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    This is the thread:
    http://forum.allaboutcircuits.com/showthread.php?t=39287

    It was not necessary to start a new thread; it simply confuses things and further delays a response. Expect for this thread to be combined with the original thread, or simply locked.

    If you haven't had a response for several days, simply add another reply to your original thread, something like "Anyone have any ideas on this problem?" That way the history is all present, and continuity of the thread is maintained.

    The board is busy, and so are the people who help. It may take days to get a reply.
     
  13. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    I have merged the two threads as SgtWookie suggested.
    You can continue here.

    Bertus
     
  14. SgtWookie

    Expert

    Jul 17, 2007
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    Sorry, but that is not the way to re-form the dielectric for aluminum electrolytic or tantalum capacitors. It IS a good way to ensure that they are destroyed. :eek:

    The way to re-form a capacitor's dielectric is to SLOWLY charge it to it's rated voltage using a current-limited source, until it's leakage rate is acceptable, or you run out of patience and decide it needs to be replaced.

    Here is a table of acceptable leakage limits:
    [​IMG]

    Have you gone through the Troubleshooting guide that starts on page 8?

    I have a feeling that your filter capacitors are fried.

    Measure from the anode of D3 to A-,. then anode of D4 to A- (each should measure ~18.5VAC) and then anode of D3 to anode of D4 (should measure ~37VAC)

    Then measure the DC voltage across C2. You should see ~25V DC.

    Perform the same tests using D5, D6, and C6 against B-.
     
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