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behringer GMX212 footswitch issue

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  • behringer GMX212 footswitch issue

    ok first off let me say I have already repaired several things in this amp since getting it, including solder underneath factory installed electrolytic capacitors, bad solder joints, loose input jack, and a former "authorized" repair centers major screw up of cutting ends off of speaker leads and wires from back panel board and connecting the speakers directly to the main circuit board ( thankfully that shop is now out of business) and it works with the exception of the footswitch which is why I am posting here tonight.

    ok when I plug in a footswitch ( not factory cause it is "discontinued" and behringer refuses to point me in a direction as to where I could buy one I ended up giving 10.00 for a randal footswitch which is compatible from everything I have found online.

    ok what it does is makes the led display go wonky and finally settl on one and at a slow random interval switches the in/out led off and on.

    ok now to the meat and potatoes as it were . the footswitch input jack is mounted to a tiny circuit board and there are 2 areas labeled c78 and c72 ( which I know are caps, it also is printed on the board in tiny lettering ( and is confirmed via the schematic) to be 100p so I know these are suppose to be 100pf capacitors. well these to capacitors are MISSING off of the circuit board and I am wondering if installing them will correct the malfunctioning footswitch issues I am having, I have narrowed it down to poor qc or the "authorized" repair shop.

    so basically are these indeed suppose to be on that circuit board to make the footswitch work? if not could it be that the amp will only recognize the factory footswitch by some means? I have already ordered the caps ( 1.99 with free shipping off of fleabay so I thought why not).

    basically I am looking for any confirmation that it could be the cause of my problems OR those missing caps have nothing to do with it, I am just trying to find out since the schematic shows them and behringer tech support was absolutely useless. see included attachment for the schematic, item in question is on page 2 and clearly labeled as footswitch
    Attached Files

  • #2
    guess I don't need to know I reflowed the solder joints inside of the footswitch itself and it started working. so I guess I'm good to go now

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    • #3
      The 100 picofarad (.0001uf) capacitors, along with the 2.2K resistors, make up an RC circuit.
      This is most probably being used as a 'debounce' for the switches.

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      • #4
        well they aren't on the little circuit board at all and the footswitch is working although the randall footswitch has SPDT switches which is the apparent reason for having to tap the switch twice to turn off and twice to turn on. I am still looking for some spst foot switches that look like the ones on MXR effect pedals that have the click to replace the ones in the randall with but so far I haven't found any yet. however, I could actually leave it as is because after all the footswitch itself is as is from randall, and the amp is working as it should, and the pedal does actually work to switch channels and turn effects off and on.

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        • #5
          The Behringer footswitch has non-latching switches. Didn't know if you were aware of that or not.
          My Peavey, crate and fender footswitches are latching type and don't work well on this amp.
          1937 Gibson L50 "Black Special #4"
          1978 Gibson Melody Maker D Reissue
          2004 Ibanez SZ720FM
          Epi SG '61 with 490R & 498T Pickups
          Couple Marshalls, Crate Blue VooDoo
          Couple 4x12 cabs
          Couple Orange combos
          TONS OF FREAKING TEST GEAR- SCOPES, METERS ,ANALYZERS
          SIG GENS, ETC, ETC, ETC.





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          • #6
            Originally posted by gearhead63 View Post
            The Behringer footswitch has non-latching switches.
            Also called momentary.
            Changing from SPDT to SPST will not solve your problem, you need to change from latching type to non-latching type.
            Originally posted by Enzo
            I have a sign in my shop that says, "Never think up reasons not to check something."


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            • #7
              Good point, GH & G-One.

              The front panel & the footswitch switches are the 'momentary' type.
              Meaning, they do not latch.
              They function to send a momentary signal to IC5, which does the actual switching of the circuit elements.

              That explains the 100pf capacitor/ 2.2K resistor RC circuit.
              They ensure a nice valid input pulse to the cpu, IC5.
              (As opposed to a ratty looking pulse that may confuse the cpu.)
              Attached Files
              Last edited by Jazz P Bass; 12-25-2014, 07:52 PM.

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              • #8
                Here is Google for: SPST momentary footswitch:
                https://www.google.com/search?q=SP+m...ary+footswitch

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