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Behringer BXL1800A problem

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  • Behringer BXL1800A problem

    I have recently come into possession of a BXL1800A. When it is powered up it sounds like an input dead short (the sound you get by grabbing the end of the input cord). None of the controls have any effect on the sound or its' amplitude. I know the basics of electronics and have looked for any obvious short conditions but nothing. Does anyone have any experience with this type of problem? Where should I start looking (besides an authorized repair shop)? Thanks.

  • #2
    First, check for DC voltage at the speaker output and let us know if you find any. It's more likely AC or you'd probably have blown a fuse or speaker by now. Still, it's a good and easy initial check. If it's AC as I suspect, my best guess is either cold/cracked solder on filter capacitors or bad caps. Check the solder on the filter caps.
    "I took a photo of my ohm meter... It didn't help." Enzo 8/20/22

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    • #3
      Thanks for the reply. As far as I can tell, there seems to be 43vdc at the speaker pins. I tested the speaker using an alternative source and it appears to be working. I can't tell if it has taken any damage but it still has full range motion. I am going to remove the electronics from behind the speaker next and check the solder joints. Will update when done.

      Finished pulling the power board out of the unit. Looks like its' had some (poor) work done on it. The 5W150RJ resistors are not soldered correctly and one of them has a broken lead. Both still register as 150 ohms but a little circuit board rework is going to be needed to get them to function correctly. I'll update when I complete the repairs, successful or not.
      Last edited by fjdukes; 01-01-2014, 09:16 PM.

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      • #4
        43Vdc on the speaker terminals is not good.

        Your output stage mosfets are most likely shorted.

        Here are two past posts on this beast that may assist you.

        http://music-electronics-forum.com/t12868/
        http://music-electronics-forum.com/t14215/

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        • #5
          Do you think getting the 2 ceramic resistors back in the circuit will cure the problem or are they just a part of the problem?

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          • #6
            I don't know which resistors you are refering to.

            Maybe use the schematic & reply with the R #.

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            • #7
              They are 5W150R ceramic resistors at positions 51 and 68 on the board. Physically they are just on the other side of the caps behind the 5 pin connector that the transformer output attaches to. Large white rectangles.

              1/2 hour later, I have reinstalled the resistors and re-established the circuit pathways. The hum is gone. Speaker voltage is 3.8vdc. Unfortunately, no sound is being produced. It looks like the speaker is being pulled in and staying there. Is this because of the DC voltage? The lights indicate that everything is working except the compressor which was working (the light anyway) before the fix. I'm going to give it and myself a rest for tonight and try again tomorrow.
              Last edited by fjdukes; 01-01-2014, 11:45 PM.

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