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Tascam DP24 feedthrough cap

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  • Tascam DP24 feedthrough cap

    On the power pcb, page 13 I think, is a feedthrough cap at the DC voltage in. It was bad, along with a diode. It was shorting the power to ground.

    The part number on the schematic shows a through hole cap. It's a surface mount on the pcb. I couldn't find the exact part so I tried;

    https://www.digikey.com/product-deta...8-1-ND/3846175

    I put it in, I have the 12vdc on the jack side of the cap but the other side I have .1 or .2 vdc. There is 0 resistance from the same 2 ends. None of the 3 conductors show a short to ground.

    Before I put it in, I put a jumper between the two ends of the cap so 12vdc would get to D313 and it worked.

    So, if the feedthrough shows 0 ohms end to end, the same as a jumper, why no DC at D313?

    Is it the wrong cap value? .022 instead of .01? I didn't think that should matter for the DC to pass through.

    Thanks
    Attached Files

  • #2
    I wonder, since it's an alternate part, if it's not contacting the traces properly. Check each end to the part it connects to. In other words, measure continuity to the jack on one side of the cap and the diode on the other. Or, check continuity from jack to diode not using the feedthrough cap for probe points.
    "Yeah, well, you know, that's just, like, your opinion, man."

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    • #3
      Yeah, that's the first thing I did cause the part is so small. I checked continuity from the jack past the cap. I also checked all 3 leads of the cap to where they should go center to ground and one end to the jack and other to d313. Continuity goes from jack positive to d313 but 12vdc does not, it's like a regular cap blocking DC, but end to end should be the feedthrough and the middle is the cap, correct? Ohm tester says yes.

      This feedthrough is acting as a filter is it needed? What is the purpose? Noise or protecting ic s?

      It's the first time I've encountered one

      Thanks
      Last edited by KCman; 11-09-2019, 02:02 PM.

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      • #4
        Are you looking at the schematic in the datasheet of the part you are using?
        I'm guessing the pin-out is different from the original part.

        https://search.murata.co.jp/Ceramy/i...223R1H3-01.pdf
        "Everything is better with a tube. I have a customer with an all-tube pacemaker. His heartbeat is steady, reassuring and dependable, not like a modern heartbeat. And if it goes wrong he can fix it himself. You can't do that with SMD." - Mick Bailey

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        • #5
          Pin 2, which is the middle contact, goes to ground. Pin 1 and 3 are the two ends. I didn't see a designator for 1 and 3, it shouldn't matter which way it goes, should it?
          The datasheet shows pin 1 in, pin 3 out and pin 2 to ground. I have pin 2 to ground.
          I don't understand the numbers written on the schematic. It shows 2 out and 3 to ground?

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          • #6
            The numbers on the schematic seem to be for some other part number, and not the one they list, which you said is incorrect anyway (through hole part that is not installed).
            So you have to make sure your part is connecting to the other components shown on the schematic.
            You said your pin2 (middle) is connecting to ground which seems to be correct. Pin 1 & 3 don't care if they are reversed.
            I'm assuming the part can be installed upside down and has contacts on both sides. So measure resistance across the top, pin 1 to 3 without touching any board traces. Should be zero ohms. If so, and the unit worked when you put a jumper where pins 1 & 3 go, you either are not connecting to the trace with your part, or there is a cracked trace or something.
            "Everything is better with a tube. I have a customer with an all-tube pacemaker. His heartbeat is steady, reassuring and dependable, not like a modern heartbeat. And if it goes wrong he can fix it himself. You can't do that with SMD." - Mick Bailey

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            • #7
              I rechecked the cap and it was no good. I ordered another just in case I fried it putting it in (it's tiny). Put the new one in and it had 12vdc all the way through, but once I tried to turn it on, it killed the cap. So, the part did not work. I figured 2 amp might work. Nope.

              How crucial is this cap?
              Can a regular cap to ground work here?

              Thanks

              Comment


              • #8
                How crucial is this cap?
                Can a regular cap to ground work here?

                Feedthrough caps are typically used as a shielding method to prevent RF noise from entering or leaving a shielded housing via the fed through wires/tracks. In your case this probably concerns the HF oscillator frequency.

                I am not able to say how crucial it is in your piece of equipment, but would try a regular small sized cap to ground (SMD or very short leads).
                Last edited by Helmholtz; 11-15-2019, 04:17 PM.
                - Own Opinions Only -

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                • #9
                  Thank you. I will try that.

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                  • #10
                    So far it's been working. I put a cap across the contacts of the dc jack and jumped it across where the feedthrough goes.

                    Time will tell. He didn't want to put the money in the new board assembly, Tascam wanted around $350. For it. They don't have just the power board available, it's multiple boards as one package.

                    Thanks

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