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Bad Cap on Networking Equipment (AXEL PLatine Terminal AX3000/M65E)

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    #1

    Bad Cap on Networking Equipment (AXEL PLatine Terminal AX3000/M65E)

    So I've got a random piece of networking equipment from a restaurant POS system, won't power up at all. Popped it open and found a ceramic capacitor that was physically broken. I've never messed with this type of capacitor before so I'm not entirely sure how to find a replacement. It's a little yellow capacitor and I think the writing on it says "4n7". Should I be able to replace this with mostly any other 4700pF capacitor?



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    #2
    Re: Bad Cap on Networking Equipment (AXEL PLatine Terminal AX3000/M65E)

    Yes, replace with ceramic capacitors, X5R or X7R or C0G/NPO , with at least 50-100v rating (input voltage should be at most 10-25% the voltage rating of the capacitor)

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      #3
      Re: Bad Cap on Networking Equipment (AXEL PLatine Terminal AX3000/M65E)

      4700pf high voltage poly cap i would use like a 3,4 or 6 kv. it looks like it is by the telephone line in. on other networking equipment they use high voltage poly caps in that area. maybe someone else could answer better.

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        #4
        Re: Bad Cap on Networking Equipment (AXEL PLatine Terminal AX3000/M65E)

        well i guess i was wrong...

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          #5
          Re: Bad Cap on Networking Equipment (AXEL PLatine Terminal AX3000/M65E)

          There's no telephone line connector in the pictures.

          In first picture, it's a AC/DC input jack... there's some ferrite for filtering and then there's 4 diodes that convert the AC coming in to DC.

          Same in second picture, nothing telephone related close to that, but it looks like that's a switching regulator there (inductor and shottky diode right by the chip is a giveaway)... the capacitors there are probably for internal oscillator, to set the frequency for the chip.

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            #6
            Re: Bad Cap on Networking Equipment (AXEL PLatine Terminal AX3000/M65E)

            It looks to me they are for noise filtering of the input power. You can easily verify that one of the leg of the cap is connected to the circuit ground, another will be connected to the power input. You can also see 4 rectifier diodes and the lytics cap close by. The unit will work without those two caps in place. So if the unit is dead, it will not be due to that broken cap.
            Show us the whole top side and bottom side of the board.
            Last edited by budm; 04-23-2014, 10:35 PM.
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              #7
              Re: Bad Cap on Networking Equipment (AXEL PLatine Terminal AX3000/M65E)

              Originally posted by budm View Post
              It looks to me they are for noise filtering of the input power. You can easily verify that one of the leg of the cap is connected to the circuit ground, another will be connected to the power input. You can also see 4 rectifier diodes and the lytics cap close by. The unit will work without those two caps in place. So if the unit is dead, it will not be due to that broken cap.
              Show us the whole top side and bottom side of the board.
              You're definitely right about it being connected to the ground and input, but for whatever reason it does seem to be the reason the unit won't power. Shorting out the leads on the capacitor allows the unit to power up fine. I've got a replacement on the way and I'll take some pics of the boards when I do the repair.

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                #8
                Re: Bad Cap on Networking Equipment (AXEL PLatine Terminal AX3000/M65E)

                you should check the inductor next to the broken cap,
                shorting the cap shouldnt change anything.

                if the inductor is good - check the 4 diodes.

                Comment

                  #9
                  Re: Bad Cap on Networking Equipment (AXEL PLatine Terminal AX3000/M65E)

                  Alright so I replaced the broken cap and another that was slightly cracked at the base (just incase). Here is the part I used. Unfortunately nothing has changed as you guys predicted. It still only powers on when shorting the capacitor, which I now realize is the same as shorting out the power to the ground. Why would that work? I can short the right side power input directly to the ground screw and it powers right on. Shorting out to the left side power input does nothing.

                  As for the inductors and diodes, you might have to bear with me a bit as I've never tested them. For the inductors I checked for continuity and found no resistance through them. I don't know what else could go wrong with them, they only have two loops and the core keeps them from touching.

                  I did get a funny reading off of one of the diodes though. They are part #N15819. The four that are grouped together all showed a voltage change of about .181V one way and no continuity the other way. However the CR3 diode showed about .176v one way and .630v the wrong way. is there any reason I would get this sort of reading other than the diode being bad?

                  More pics as promised:







                  Comment

                    #10
                    Re: Bad Cap on Networking Equipment (AXEL PLatine Terminal AX3000/M65E)

                    That LT1376 is a buck (switching) regulator, it takes input voltage and produces lower voltage:


                    CR3 is D2 in the picture above.

                    That CR3 diode is critical for its operation and should only show measure voltage ( that 0.176v) in one direction. As it measures something in both directions, it may be bad... So it would be best to desolder at least one leg of that diode and measure it with one leg in the air, or completely out of the circuit.
                    Do that and get back to us.

                    Comment

                      #11
                      Re: Bad Cap on Networking Equipment (AXEL PLatine Terminal AX3000/M65E)

                      Alright it's not the diode. With the board removed and the CR3 diode desoldered they all read the same at .176v. That diode only gives me a reading in the opposite direction when the board it's on is plugged into the bigger board.

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                        #12
                        Re: Bad Cap on Networking Equipment (AXEL PLatine Terminal AX3000/M65E)

                        With the small board disconnected from the large board and plugged into the DC jack and power button pressed, do you get 5v on the connector?

                        The connector is simple.. two pins are ground, two are 5v .. as far as I can tell from the second picture.
                        If you have 5v, then this board is probably fine and the issue is on the other board.

                        On the larger board, with it not connected to anything, measure the resistance between voltage pin and ground (two + , two - in the connector, pick one + and one - )
                        Check those tantalum capacitors (the small yellow ones), see if they're shorted, if you can measure the capacitance as well.

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