help with a possible power supply issue

Discussion in 'General Electronics Chat' started by bill l, Nov 17, 2009.

  1. bill l

    Thread Starter Member

    Oct 11, 2009
    30
    0
    ok, i now have to resort to asking for some help with this issue.

    i previously posted asking for anyone that has a fluke 8010a or 8012a dmm to take some voltage readings for me, but no luck.

    i have the service manual for this unit and the specs come from that.

    below is the image of the power supply portion of the schematic.

    the service manual calls for the voltages as printed in blue, but, these voltages are based on the non battery operated version. unfortunately, i have not been able to find any voltage specs for the battery operated version.

    in 1984, an addendum was made that changed a resistor and a cap in the timing circuit and the addendum also made change that the table for voltages from the battery operated supply to meet the specs that are listed in blue on the image below, which is the same specs as the a.c. only meters.

    the battery pack consists of 2 sub c cells for a total of 2.7vdc 2 ah.

    voltage from the battery in on condition is 2.72vdc and delivers 150ma.

    my concern is the + and - 15 volt spec.

    i have scoped the outputs of q6 and q7 and duty cycle is approx 70% on. i will add pics of these later to help.

    i am confused that fluke would call for the battery operated version to hold the same specs as the a.c. only version without having a prior table specifically for the battery operated version.

    i think there is a problem somewhere as i played a little with r25 and noted that changing that resulted in the + and - 15 vdc coming into specs, BUT, upon turn off and turn on, the clock cycle would not start unless the r25 was within it's original spec of 4.3k.

    can you guys give me a hand with this?

    i'll update with pics of the scope later.

    thanks

    bill
     
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  2. someonesdad

    Senior Member

    Jul 7, 2009
    1,585
    141
    Hi, Bill:

    You might write a sentence or two about what problem you're trying to solve -- it's easy to get caught up looking for insects in the bark and forget to explain what's wrong with the forest... :)
     
  3. bill l

    Thread Starter Member

    Oct 11, 2009
    30
    0
    thanks for the reply.

    yeah, suppose i should have written something, although the pic shows the read values along with the specs as called for by the service manual.

    the issue:

    +VA should be +15 vdc +/- 1v
    -VA should be -15 vdc +/- 1v

    but actual readings are +10.8 and -10.9
     
  4. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Bill,
    You're asking mighty specific questions pertaining to just Fluke 8010a or 8012a battery powered DMM's. It would be great if someone who had one would reply, but unless that happens the best we can do is just give very generalized help.

    If you don't get a reply within a reasonable period of time, my best suggestion would be to contact Fluke themselves; as they would be the ultimate authority on their products.
     
  5. bill l

    Thread Starter Member

    Oct 11, 2009
    30
    0
    thanks sgt.

    unfortuantely, fluke does not provide much support for these anymore other than still selling some parts for them.

    i agree, until someone that has one pops up and give readings, i'm not too hopeful that this is going to be an easy thing to dissect.

    i have not found a whole lot about astable transistor vibrators and it's been such a while since i have worked on this kind of stuff that i'm not sure that it's set up to be an astable, but seems more like a retrig type.

    i am suspecting that if there is in fact a problem with the 15v, i am thinking that the rc network there may be the issue.

    but again,

    don't really know if in fact that is an issue to begin with.

    bill
     
  6. studiot

    AAC Fanatic!

    Nov 9, 2007
    5,005
    513
    Since this is an old device I suggest you check the state of the electrolytics.

    C26/C27 are likely to be OK since the +/- supply is symmetrical, but C22,C23 and C24 bear investigation.
     
  7. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    I kinda cringe seeing caps rated at 16 volts in a 15 volt circuit. There's no room for a glitch.
     
  8. bill l

    Thread Starter Member

    Oct 11, 2009
    30
    0
    good catch on that.
     
  9. k7elp60

    Senior Member

    Nov 4, 2008
    478
    69
    I have a 8012A that is working. It doesnot have the battery option. If you like I can take some voltage readings.
    Ned
     
  10. bill l

    Thread Starter Member

    Oct 11, 2009
    30
    0
    thanks k7, but the power supply circuit is totally different in the ac only version.

    just out of curiosity, you have verified that you don't have the circuitry for the battery pack? (hoping you do have it..... :) )

    do you need a copy of the service manual for yours? i have a copy if you need one.

    bill
     
  11. k7elp60

    Senior Member

    Nov 4, 2008
    478
    69
    Bill I looked inside and mine does not have the battery option. I do have a schematic and mine is working fine. It was calibrated about 2years ago.
    Here are some voltage reading taken with a Fluke 87V meter.
    TP8 also marked as -VA -14.87 volts
    TP8 also marked as VDD +2.86 volts
    TP10 also marked as +VA +14.96 volts
    TP7 also marked as VSS -7.52 volts
    From the schematic this all appear to be unregulated so the line voltage here could affect them.
    They were all checked with the common lead of the DVM on ground side of R34(47M 1/2W)resistor.
    Perhaps this will help.
    Ned
     
  12. bill l

    Thread Starter Member

    Oct 11, 2009
    30
    0
    got it worked out.

    apparently, fluke service info as i have it is incorrect.

    the +10 and -10 are in tolerance for the battery operated units.
     
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