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repairing the DT830B digital multimeter

Discussion in 'Repairing Electronics' started by mdanh2002, Nov 12, 2010.

  1. mdanh2002

    mdanh2002 Member

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    I recently purchased a DT-830B digital multimeter, something like this The DT830B pocket-size digital multimeter, from ebay. The item arrived early and the packaging seems intact. However, when I powered it up using a newly bought 9V battery, it doesn't seem to work. Switching the dial will only move the decimal point on the LCD, and display the "HV" warning if the dial is in high voltage range. Nothing else seems to work, I can't measure voltage or resistance, nothing else is shown on the display. Even worse, the LCD will fade away and become blank after 5 seconds if the dial is not moved.

    At first I suspected the battery, but replacing the battery does not help. I use my analog multimeter to check the fuse onboard and it seems OK.

    Anything else I could do to fix the multimeter?

    Looking forward to any advice. Thanks.
     
  2. ben7

    ben7 Member

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    That is why you never buy stuff from ebay!
     
  3. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    Buy another. This is probably it for $3.99. 7 Function Digital Multimeter

    I'm lucky, I guess, I have a store nearby. Gas cost might tbe half the cost of the meter. You can get a backlit version for 4.99. I got mine free from a power supply manufacturer. Goes nicely with the Flukes, Keithleys and HP/Agilent mutimeters at home.
     
    Last edited: Nov 13, 2010
  4. dave

    Dave New Member

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  5. mdanh2002

    mdanh2002 Member

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    I guess luck was not on my side. I will contact the seller to see if he's nice enough to refund me, or re-send me another unit. I don't believe that the seller deliberately sells faulty unit, my multimeter might have been damaged during shipping. Is it really that easy to damage a multimeter (the packaging was adequate and intact when I received it)?
     
  6. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    It's very difficult to damage a multimeter. There is a fuse, but usually it's for current only. All I would do is to check for loose parts, but I'll bet you did that already. Postage shipping it back may kill you. It's worth a shot to ask. Electronics suppliers will tell me to keep the parts if I got the wrong ones. Sometimes I've had to mail them a pic.
    It's silly tp ship back a single part that costs $2.00.
     
  7. mvs sarma

    mvs sarma Well-Known Member

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    In fact it is very easy to damage the DTxx38 range of DMMs. Off late they are assembled using SMD resistors The moment you try to measure AC voltage or AC current, these resistors burn. I have one such sample that burnt off in moments after purchase.
     
  8. tvtech

    tvtech Well-Known Member Most Helpful Member

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    I honestly wonder why this crap is allowed onto the marketplace...

    Quality standards are non-existent anymore. And getting worse by the day.

    You should see some of the factory rubbish that I fix on a day by day basis (TV's). A chassis where the Mains fuse is soldered directly to the PCB. With wire.

    That means "throw away when faulty". "Do not attempt repair". Chinese :mad::mad::mad:
     
    Last edited: Nov 14, 2010
  9. mvs sarma

    mvs sarma Well-Known Member

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    the human desire to get things cheap and encourage purchasing cheap ones.
    If there is no taker, the manufacturer wont dare to make things
     
  10. tvtech

    tvtech Well-Known Member Most Helpful Member

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    These TV's are not cheap for a Consumer to buy. They are sold at a price equivalent to any other similar Chinese TV. The customer does not know what junk lies within the smart box. Only when it breaks does the truth hit him/her.

    Everything sold here ATM is from Chinese factories. Be it Panasonic, Orion, Hey Wow, Hey Hoo, Telefunken, Philips, Recor, Sanyo, Advance, Aim, Akira, Dixon, Kingsonic etc, etc, etc.

    All the same crap. Sometimes built a little better though. Bigger heatsinks. Inevitably the same PSU design.
    I friggin hate copy cat's. Are these MF's not capable of doing anything original?. Or making a design that stands out???

    All a bloody Chinese can do is copy. Originate and think...No.

    It's way easier to steal ideas and designs and build the products cheaper.

    Chings are a nation of fakes.

    And the Consumer does not have a clue. Would you?

    Cheers
     
    Last edited: Nov 14, 2010
  11. ben7

    ben7 Member

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    Chinese stuff breaks all the time. Our Panasonic 32inch LCD TV has gone on the fritz, radomly beeping every few hours. Sometimes it beeps, sometimes it doesn't for a day or two; but ironicly it still works!

    I thought Panasonic stuff was good quality! :mad:
     
  12. tvtech

    tvtech Well-Known Member Most Helpful Member

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    It was/is good. Except here in sunny SA.
    As a Tech if a TV says "Panasonic" on the outside these days any house of horrors could await you on the inside.....

    Chings

    Said enough :mad::eek:
     
  13. mdanh2002

    mdanh2002 Member

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    I decide to try again today, checking for loose connection. See the attached photo:

    [​IMG]

    I pressed hard on the part highlighted in red (what is the proper name for it?), trying to adjust it, and at some point the LCD starts to show something like 8888 or 0000. Suspecting that there is a loose connection somewhere, I tried hard but could not make the meter do anything else useful. Anyone knows why what I did causes the multimeter to become somewhat alive?

    Also just curious, how do you call the part highlighted in yellow?
     
    Last edited: Nov 19, 2010
  14. tvtech

    tvtech Well-Known Member Most Helpful Member

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    That's a trimmer pot (red area). Probably for calibrating the meter.

    Cheers
     
  15. ModemHead

    ModemHead Member

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    The part in yellow is a clone of the ICL7106 A/D converter and LCD driver. A lot of inexpensive DMMs, panel meters, etc. use this chip. It is a "chip-on-board", meaning the silicon die is glued directly to the PCB and covered with a blob of epoxy. Cheaper to manufacture this way.

    As for seeing things on the LCD, just touching the PCB traces can cause random things to be displayed. Also, the flexible connector between the PCB and LCD requires compression for good contact, so pressing on parts can cause also random display patterns.

    And yes the trimmer is for calibration. So if you got lucky and and the meter started working, it would be un-calibrated now.
     
  16. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    The blob has the proper name of "IC die". See International Rectifier - Die Products

    See ic die - Google Search

    Wires are ultrsonically bonded to the pads and covered with epoxy. I used to use an ultrasonic bonder.

    Your loose connection, could very well be under the black blob.

    Note that it has a regular IC pad around it, so resumeably an IC of the right package could be soldered there.
     
    Last edited: Nov 21, 2010
  17. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    Sorry, it's more correctly known as COB, the die is the actual silicon - either in a COB or a normal IC.

    Die Products Consortium: Chip on Board Tutorial
     
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  18. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    Oh well. Got all the parts right. Thanks.
     
  19. mdanh2002

    mdanh2002 Member

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    Thanks all for the info. I learned something new, even if the multimeter can't be used :)

    I contacted the seller (a guy from China) and got a full refund. There are still many good and responsible sellers on ebay :)
     
  20. ss joshi

    ss joshi New Member

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    iwant circuit diagram of dt830b
     
  21. absf

    absf Active Member

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