Connect with us

HP 400F AC voltmeter

Discussion in 'Troubleshooting and Repair' started by vecher, Oct 16, 2017.

Scroll to continue with content
  1. vecher

    vecher

    3
    0
    Oct 16, 2017
    My ac voltmeter will not zero any more .., Anyone have a manual or schematic for it? Or what do I check.. It was working but lately it will not zero on any scale The lower the scale the worst..

    Thanks'
    Skip
     
  2. FuZZ1L0G1C

    FuZZ1L0G1C

    368
    117
    Mar 25, 2014
    Is it a panel meter?
    Might be that needle has bent from 'pinning'.
    Or plastic zero-cam may be worn or cam-pin broken.
     
  3. dorke

    dorke

    2,342
    665
    Jun 20, 2015
    Welcome to EP.
    Here is the operation and service manual of the HP 400F/FL.
    Are you able to get mechanical zero?
     
  4. 73's de Edd

    73's de Edd

    2,872
    1,216
    Aug 21, 2015
    Sir Skip . . . . .

    INITIALLY . . . . . with no power applied, check to see where your meters mechanical pointer setting is having
    the meter pointer being positioned, as relevant as to how close it is initially being, to scale ZERO.
    Then check out the meter amp and bridge circuitry for its +- 26V's supplies and derived -6 and 9V supplies.
    Also check out how well and balanced the YELLOW squared electrolytics are holding up after being 50 years old.
    This was a military / aerospace microfiche schematic, so I further magged it up enough to make every small
    component marking readable.
    Certainly beats the service manuals piecemeal schematic sheets, if you have to travel across sections.

    Re . . . .REFERENCING:

    [​IMG]

    73's de Edd
     
  5. vecher

    vecher

    3
    0
    Oct 16, 2017

    Yes

    As I go down in ranges the meter reads higher.. Does not maintain 0 Even at highest ranfe metrr is still not at 0 but pretty close.. This is with no input and terminals not shorted together..

    Skip...
     
  6. dorke

    dorke

    2,342
    665
    Jun 20, 2015
    You do need to short the input terminals together, i.e. Vin=0,
    the lower the input range the more important that is!
    Do that with the shortest possible wire.
    Still no zero?
     
  7. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,386
    2,772
    Jan 21, 2010
    I recommend you check A2Q15, A2Q16, A2Q17, A2C38, A2C39, and A2C40.

    These are the components commonly associated with a meter deflection with no input.

    Edit: Edd has already suggested looking at those caps.
     
  8. vecher

    vecher

    3
    0
    Oct 16, 2017

    Ok I will check tomorrow.. Thanks

    Skip...
     
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day

-