Multimeter broke!

  1. Since it's my first time playing around with a multimeter, i finally short-circuited it, tried to measure a current incorrectly, so now my fuse is burnt...
    The problem is, the fuse is soldered on my multimeter. What should I do, get another multimeter or get a soldering gun and try to fix it? (the latter seems more exciting, but it will suck if it wont work)

    Thanks in advance...
     
  2. jcsd
  3. dlgoff

    dlgoff 3,045
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    Should work. That's why fuses are used; to protect the multimeter circuit in this case.
     
  4. So if I got a gun I could melt the sides and stick another fuse there?
     
  5. berkeman

    Staff: Mentor

    Yes. You can desolder the blown fuse and solder in a new one with the same rating. The trick may be finding a similar fuse.
     
  6. No that was actually very easy. Got a pack of 10 for 1 euro in an electronics store. The problem is I have no gun so if it's expensive I'll probably buy a new multi...
     
  7. berkeman

    Staff: Mentor

    Can you post a photo? There might be another way to handle it...
     
  8. Here you go
     

    Attached Files:

  9. berkeman

    Staff: Mentor

    You might be able to make 2 little spring clips to hold the good fuse up against the blown fuse's body, just below it on the PCB (as long as it doesn't short to any other exposed metal or parts). As long as the fuse ends are touching each other (the fuses will be in parallel), it should function fine. It's a pain that they soldered the fuse to the PCB!

    If you do use a soldering gun (maybe you can borrow one from someone), you will need solder wick to clean off the existing solder to free up the blown fuse.
     
  10. Well I can't find someone who has a soldiering gun so I guess I'll take it to an electronics store and see if they'll repair it...
     
  11. berkeman

    Staff: Mentor

  12. dlgoff

    dlgoff 3,045
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    In this case, probably the best solution, as the fuse may have a fast-blow at a small current and heat from a soldering iron/gun might open the new fuse.
     
  13. berkeman

    Staff: Mentor

    Good point! If the shop replaces the fuse, they should solder down two fuse clips, instead of soldering the fuse itself down. That makes future replacements a *lot* easier.
     
  14. Thanks for the help. I'll update you tomorrow. Unfortunately there isnt enough space for such fixes, it's a "portable" multimeter...
     
  15. AlephZero

    AlephZero 7,300
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    Homework Helper

    The picture certainly looks like an ordinary wire fuse in a glass envelope (so you can see if it has blown), but soldering that directly into the circuit seems weird. How would you hold the fuse in place while soldering it? And how would you apply the heat directly to the joint?

    Are you sure it's not held between two bits of springy metal pressing on each end of the fuse, maybe with a blob of glue to stop it jumping out of place if you drop the meter? In other words, something cheaper than the "proper" fuse clips in dlgoff's picture?
     
  16. First connect the meter to something (safe) you want to measure and then short the fuse with a small piece of wire. At least then you know whether it is worth replacing the fuse.

    I don't like soldering guns. Soldering Irons are easier to use and probably cheaper. (not sure about price, my magnetic tip weller is over 40 years old so I haven't shopped around). If you buy an iron, also buy a solder sucker and solder wick and you are setup. Also, don't leave it on for long periods (the tip oxidizes).
     
  17. jim hardy

    jim hardy 4,515
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    Soldering guns have got expensive. I buy mine at yard sales and junkshops, have about six of them.
    A soldering iron is better for small work anyway. They are comparatively inexpensive and will last a year or two.

    It is a little tricky to solder to the endcaps of a fuse without melting the internal wire - takes a gentle hand and you have to be quick. So be glad you have a few extra fuses.
    There exist fuses with wires already soldered on the ends, just for printed circuit board applications.

    Looking at your picture, i think it's worth a try.
    Clean your new fuse's metal caps with fine steel wool and apply solder flux.
    Then apply heat at the end of the metal fuse cap, down where it contacts the solder pad on circuit board.
    You want to see the solder melt and flow onto the metal fusecap. Remember solder follows heat, so drag your iron's tip up the end of fusecap then away. Solder should follow.

    Might take a few tries. But you NEED to learn to solder. If you can find some old 60/40 solder , it is easier to flow than this new lead-free stuff(which i hate).

    [​IMG]
    http://www.amazon.com/Kester-Rosin-Core-Solder-Spool/dp/B00068IJPO
    "Kester44 forever !!!" I have about five pounds of it, a lifetime supply for me.
    Any other brand will work as well, just be sure it's rosin core not acid.
    You want 0.031" or a little smaller for general electronics repairs like this.


    old jim
     
  18. sophiecentaur

    sophiecentaur 13,405
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    Unless you are very hard up or so old that you will never do any more electronics stuff, you should seriously consider buying a soldering iron. They are so useful and, as long as you clean the tip afterwards, they can do other small jobs like cutting nylon cord and rope without letting it fray, welding / mending small plastic items. If you are considering a new DMM then mend this one and you that will release money for your soldering iron purchase.

    BTW, do not ever try to replace the fuse wire with anything other than 'proper' fuse wire, which is a tin alloy and behaves very differently from a thin length of copper wire.
     
  19. AlephZero

    AlephZero 7,300
    Science Advisor
    Homework Helper

    Cheap soldering irons are pretty horrible to work with, compared with a good temperature controlled iron.

    If you are seriously interested in electronics, save up and buy a GOOD soldering iron with temperature control, a reasonable power rating (say 50 or 60 watts) and interchangeable iron-coated bits. A price tag in the $50 to $100 range might seem expensive, but it will last you for 50 years, not one or two. The trouble with cheap low power irons is they overheat if they are left switched on and not used, but they don't have enough heat capacity to deal with the times when you need to solder something big, so you lose out both ways in terms of ease of use. And iron coated bits don't need endless cleaning, filing into shape, and tinning. Just dab the hot bit on a damp sponge, and the "steam clean" makes it like new again.
     
  20. jim hardy

    jim hardy 4,515
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    Every word of above is true.

    for a one time repair on a $10 multimeter, , borrow a good iron or buy a cheapie.

    If you get interested in electronics work, which is a LOT of fun,
    you'll soon crave a really good iron.

    http://www.ramseyelectronics.com/Hobby-Kits/b/6290126011
     
  21. So here's the update:
    I went to an electronics store with my multimeter and spare fuses, the guy working there was kind enough to solder it for free so I bought some 555 IC and capacitors from him. The multimeter works like a charm! :D

    But I'm considering getting a soldering iron myself, I was curious how much it would cost, so I went in a hobby store and they had soldering irons for about 5 euros. Might get one soon.
     
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