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Bi-polar transistor help - APC NetBotz 455

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    Bi-polar transistor help - APC NetBotz 455

    All,

    Troubleshooting an APC NetBotz 455 environmental monitoring device. I've had this on my "to fix" shelf for a while and got a hair tonight to look at it. Did some standard troubleshooting first...visibly inspected the boards, no blown caps, no burn marks, nothing "appears" out of the ordinary. Re-seated what would be considered the motherboard, checked the CMOS battery for proper volts, nothing else is jumping out at me.

    Got out my multimeter and started probing points on the board that were labeled with voltage readings.....getting nothing other than small blips. This is a POE device and plugged into my midspan it just cycles power quickly on, then off for several seconds, over and over. Decided to get away from the midspan and used a dumb POE injector. Started getting rapidly fluctuation voltage readings and the same points I was measuring before, plus noticed a could LED lights on the board rapidly flashing. Next I was going to start working my way up the board from the power source (network cable) and went to test my first voltage regulator on the board and suddenly the lights when solid and it booted up. Unsure of what I did I cut power and tried again....same thing.....quickly flashing lights. Tried testing the voltage regulators that I "thought" I had started with but just kept getting fluctuating readings again. Moved to what I thought was a smaller VR and touched the negative probe of my multimeter to pin one, and it started booting up again.

    Since figuring out what I did this is very repeatable. I don't need both leads on the multimeter, just need to touch one of the leads to pin one on the IC, which looking closer is not a VR, but is a bi-polar transistor. New to me....I know what transistors are, but never heard of a bi-polar transistor. I've included a couple pics showing a larger view of the board(s) as well as a close up of the bi-polar transistor in question. Below is a data sheet link I found for this transistor:

    https://cdn.badcaps-static.com/pdfs/...22bcc52bd3.pdf

    If someone could be so kind as to take a look at the datasheet and the pics, and give me your thoughts. Still getting my feet wet at component level repair with anything greater than re-capping a board or working with resistors and diodes....I can't believe it would be as simple as replacing the bi-polar transistor, and won't be surprised if it's believed to be another component and I just discovered a symptom/by-pass.

    Thanks!!!
    Attached Files

    #2
    Re: Bi-polar transistor help - APC NetBotz 455

    So did you try re-soldering all 3 pin of that NPN Transistor?
    Never stop learning
    Basic LCD TV and Monitor troubleshooting guides.
    http://www.badcaps.net/forum/showthr...956#post305956

    Voltage Regulator (LDO) testing:
    http://www.badcaps.net/forum/showthr...999#post300999

    Inverter testing using old CFL:
    http://www.badcaps.net/forum/showthr...er+testing+cfl

    Tear down pictures : Hit the ">" Show Albums and stories" on the left side
    http://s807.photobucket.com/user/budm/library/

    TV Factory reset codes listing:
    http://www.badcaps.net/forum/showthread.php?t=24809

    Comment


      #3
      Re: Bi-polar transistor help - APC NetBotz 455

      I did....can't believe I didn't think of that, but it didn't make a difference. Further testing shows I can jump-start it with any piece of metal touched to pin one. Looking at the traces, I can also do the same thing by touching a metal object to the left side (as oriented in the close-up picture) of R13.

      Seems like touching these items introduces a slight change in something....capacitance?? Doesn't make a lot of sense to me so what am I missing or not understanding?? I do know that touching those items with something non-conductive has no effect.

      Thanks!!
      Last edited by raregtp; 03-24-2020, 03:04 PM. Reason: Added more info.

      Comment


        #4
        Re: Bi-polar transistor help - APC NetBotz 455

        Originally posted by raregtp View Post
        I did....can't believe I didn't think of that, but it didn't make a difference. Further testing shows I can jump-start it with any piece of metal touched to pin one. Looking at the traces, I can also do the same thing by touching a metal object to the left side (as oriented in the close-up picture) of R13.

        Seems like touching these items introduces a slight change in something....capacitance?? Doesn't make a lot of sense to me so what am I missing or not understanding?? I do know that touching those items with something non-conductive has no effect.

        Thanks!!
        Bodge a piece of metal to it and it'll make a semi-decent entry to the ghetto mod thread!
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          #5
          Re: Bi-polar transistor help - APC NetBotz 455

          While it's temping......I'd really like to figure root-cause this thing. That said, a curious thought is if I'm already touching the terminal on the resistor when I first power it up, will it immediately boot or is it the change after it's powered up that's allowing it to boot. Off to do further testing!

          Comment


            #6
            Re: Bi-polar transistor help - APC NetBotz 455

            The pin that you touch is the Base of the Transistor, but we do not know if it is setup as a amplifier or what.
            Does heating and cooling have any effect?
            When touch the pin you may have applied stray capacitance or resistance, so you may try low capacitance or high resistance between Base and Ground to see what will happen.
            Never stop learning
            Basic LCD TV and Monitor troubleshooting guides.
            http://www.badcaps.net/forum/showthr...956#post305956

            Voltage Regulator (LDO) testing:
            http://www.badcaps.net/forum/showthr...999#post300999

            Inverter testing using old CFL:
            http://www.badcaps.net/forum/showthr...er+testing+cfl

            Tear down pictures : Hit the ">" Show Albums and stories" on the left side
            http://s807.photobucket.com/user/budm/library/

            TV Factory reset codes listing:
            http://www.badcaps.net/forum/showthread.php?t=24809

            Comment


              #7
              Re: Bi-polar transistor help - APC NetBotz 455

              What are the numbers on IC5?
              2252?
              [Ti logo] 92?
              A22?
              I suspect it is a TLC2252C op-amp, If it is, then pin 1 is the [1out] so I suspect either the ic is faulty or the input has an issue.
              It looks like the ic monitors the current through R36~38, IC12 is a shunt regulator.
              I see PROBE_VCC, It could be that the circuit monitors this voltage?
              Last edited by R_J; 03-30-2020, 09:51 PM.

              Comment


                #8
                Re: Bi-polar transistor help - APC NetBotz 455

                Apologies for the long delay in replying......work from home with e-learning and everything going on in these strange times has been kicking my butt!

                Looks like you were spot-on on those numbers. It is a 2252A, 92T, A22J. See attached pic.
                Attached Files

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