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Discussion in 'Troubleshooting and Repair' started by ocamargo17, Feb 9, 2014.

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  1. ocamargo17

    ocamargo17

    1
    0
    Feb 9, 2014
    I just wanted to say hi and introduce myself, my name is Orlando. I am electronics enthusiast. I am a novice at best but I would like to learn as much as possible. I have had an electrical class when I attended a post secondary technical school for automotive, so I know the very basics and what I learned in school didn't really have too much to do with more of the commercial electronics. So I figured I would join a electronics forum just in case I ever need help from people who are much more knowledgeable in this field than I.

    Anyway as my first little project I stumbled upon a stud finder that no longer works and I thought this would be a good beginner project to see if I could get it work again. Right now there is no power getting to it and the battery is brand new. The circuit board isn't cracked or anything. Any suggestions as to what should be my first step in diagnosing the problem?

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    Last edited: Feb 9, 2014
  2. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
    1,268
    Nov 28, 2011
    Hi Orlando, and welcome to Electronics Point :)

    With an unfamiliar unit like this, I would start with the multi-pin components. Your first photo shows a 16-pin SOIC (small outline IC) on the track side, and the second photo shows a 24-pin DIP (dual in-line package) on the other side. There are also several three-pin components on the track side; these are likely to be junction transistors or MOSFETs, and one of them is probably a regulator.

    Generally, large ICs have limited supply voltage ranges, and operate from less than 9V, which is why I suspect there's a three-terminal regulator there somewhere.

    Follow the tracks from where the battery snap connector connects to the board. Usually the negative side connects to the circuit's main ground rail, also called the 0V rail ("zero volt rail"), which is the place where voltages are measured relative to.

    There will probably be a MOSFET or transistor in series with the battery, controlled by the pushbutton, so that when the device is OFF, no current flows out of the battery, so it doesn't go dead. This part of the circuit, and the regulator, would be likely culprits for this fault description. For example, if the battery was connected around the wrong way, even briefly, the MOSFET and/or the regulator could have been damaged. Properly designed circuits have protection against reverse battery connection, but many budget products are designed based on price, not quality or reliability.

    It's difficult to identify small SMT (surface-mount technology) components because their markings are encoded (there's not enough room to print "BC847B" so they print something like "F8A"). There are sites where you can look up SMT markings but I don't know their names; use Google if necessary.

    Once you have the part numbers, look them up using Google or a supplier site like http://www.digikey.com or http://www.mouser.com. These sites have a huge range of components, and links to data sheets, and are a great source of information on most modern parts. Old parts can sometimes be found through Google. Some Asian parts don't have Internet-accessible documentation.

    Then you download the data sheets and have a read of them, to see what the components do. This should give you a general idea of what the different parts of the board do, and for this fault, you should be able to trace the battery voltage through to the regulator, and measure some voltages with a multimeter to figure out where it stops.

    Please feel free to post some close-ups of the board and ask any other questions you may have.
     
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