Fluke 77 Multimeter stopped reading current

Discussion in 'General Electronics Chat' started by bluebrakes, Sep 4, 2011.

  1. bluebrakes

    bluebrakes Thread Starter Active Member

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    Hi,

    my old faithful fluke 77 multimeter has stopped reading DC and AC current.
    It still reads Ohms, Volts and continuity, just not current. :confused:

    I found this guide here...
    http://assets.fluke.com/manuals/75_77___omeng0900.pdf
    although it doesn't help that the 77 pcb is slightly different to the diagram shown. i.e. I don't have a couple of the components or two fuse holders in mine.

    With components being tested with another multimeter still on the fluke 77 pcb, nothing seems to be faulty. I checked the fuseable resistors and i can't seem to find anything faulty.

    Has anybody else had this problem or know what component could be at fault?

    Thanks. :)
     
    #1
  2. bluebrakes

    bluebrakes Thread Starter Active Member

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    photo attached of my fluke 77 board.
     

    Attached Files:

    #2
  3. someonesdad

    someonesdad Senior Member

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    The cause for not reading current is usually one or more blown fuses, especially if the other functions work. Since your PCB doesn't have fuse holders, then the fuses must be less obvious components -- maybe you should do a continuity test on all the components.
     
    #3
  4. t06afre

    t06afre AAC Fanatic!

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    Take a look from page 27 and out in your manual. I think I see one empty fuse holder in the picture. But you should have 2 fuses. And I can not see the the small fuse holder at all
     
    #4
  5. wmodavis

    wmodavis Active Member

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    You likely left the red probe in the 10A or 300mA and tried to measure a voltage source that when presented with a near short circuit, dumped enough current into the meter to blow the replaceable fuses.
     
    #5
  6. praondevou

    praondevou Well-Known Member

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    this fluke77 looks different, like in your manual... why? sure your is a 77?
    [​IMG]
    [​IMG]
     
    #6
  7. praondevou

    praondevou Well-Known Member

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    Last edited: Sep 4, 2011
    #7
  8. hgmjr

    hgmjr Moderator

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    Make sure you replace the fuse with the proper Fluke fuse.

    hgmjr
     
    #8
  9. Jaguarjoe

    Jaguarjoe Active Member

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    Aren't those fuses like $10 or so? I popped one of mine and learned to be very, very careful when measuring current. Mistakes are costly.
     
    #9
  10. R!f@@

    R!f@@ AAC Fanatic!

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    Hmm.!! Where can I find fluke fuses.
    I need plenty, cause I use like what comes my way.
     
    #10
  11. praondevou

    praondevou Well-Known Member

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    #11
  12. PackratKing

    PackratKing Well-Known Member

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    my 77 Definitely looks like the board pictured in #6, with the large fuse on the 10 amp function.

    Fluke would shoot me, but I modified my 77.

    I opened it, and ran wires out from the 300 milliamp circuit, and the probe sockets into a small project box. I no longer need to change leads around for different measurements, as leads are selected on a rotary wafer switch, and a small fuse on the outside of the box so I don't have to open the unit to change fuses.

    If and when I get brave enough, or really need to, I'll move the 10 amp fuse leads to the outside, and wire it to a resettable breaker. I have other "expendable" ammeters though, and refuse to abuse my Fluke.
     

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    Last edited: Nov 28, 2013
    #12
  13. someonesdad

    someonesdad Senior Member

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    For you folks who modify your digital multimeters, realize that not using the recommended fuses can significantly change the safety protection of the meter. Those $5-$15 fuses in the Fluke meters are typically rated for class III and class IV service. Those fuses are capable of safely handling transient overloads of currents in the 10 to 100 kA range; such currents can be expected from voltage transients in class III and IV service areas. These fuses are specially designed to extinguish the nasty arc plasmas that can result from such high currents, protecting the instrument and you from nasty burns.

    If you're not familiar with these ratings, read your meter's manual and do some web searching. Don't make the mistake of thinking that class III/IV stuff is only for industrial electricians working on industrial stuff -- you can probably find a class IV situation around your own home. And, once you understand the risks and protections needed, you'll be thankful that your DMM is properly designed to protect you. If you're curious, search the web to find a 2003 Fluke document entitled "Electrical measurement safety" -- it has a few eye-opening pictures, especially the one showing the fingerprints burned into the probes.

    That said, one of these days I'm going to buy some AGC fuses with the same ratings as my Fluke's fuses. Then I'll make an adapter to take these fuses instead of the Fluke-spec'd fuses. This will let me use my DMM on the bench without worrying about blowing ten bucks when I accidentally put too much current through it. However, I will put a prominent sign on the front of the DMM saying "Class I operation only!".
     
    #13
    PackratKing and R!f@@ like this.
  14. debe

    debe Active Member

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    Ive been using ceramic fuses that are designed for large currents at 240V. These fuses are used in the mains side of microwave ovens & are under $1 ea. in M205 & 3AG sizes. They are also filled with a flame retarding powder.
     
    #14
  15. t06afre

    t06afre AAC Fanatic!

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    If you use fuses from a well known manufacturer. That are approved. And follow the spec from Fluke. You should be OK. But using no branded simple glass fuses. May not be the best.
    I often use fuses from littelfuse http://www.littelfuse.com then I need fuses I can trust. I think my Fluke came with a littelfuse fuse for the hi amp range
     
    #15
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