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Behringer SL2442FX , mixer desk, 2004

Discussion in 'Electronic Repair' started by N_Cook, Feb 4, 2012.

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  1. N_Cook

    N_Cook Guest

    This 24 ch mixer has been "repaired" twice for a very rare random fault.
    Recurs
    months after being "repaired". Loss of L channel output at the XLR. Previous
    person had obviously looked at the most likely suspect of the 1/4 in sockets
    for insert , with bypass contacts and XLRs thmselves.

    Both Main/Sub push-push switches, 4 pole C/O are very suspect in the FX
    sections, half a mm pushing when out will loose the effects component of L
    or R channel and a bit more, full loss of one or both channels. Any other
    suspects to check?

    I'm surprised the schema are out there but minus smps so some details taken,
    just in case.
    switcher driver ? (reverse of pcb not explored) maybe designated
    04N68, TO220 , usual 0/O possibility (obstructed viewing) other marking
    maybe 1M360
     
  2. N_Cook

    N_Cook Guest

    googling around turned up

    "Incidentally, on more than one occasion I have repaired a Behringer with
    this exact same symptom (no L ch), and it turned out that one of the main
    bus tracks
    runs right at the far right edge of the PCB from fader to output jack socket
    section. When the PCB was installed into the chassis, something sharp
    caught on the PCB and partially cut through the track, which eventually
    failed some time later."

    for when I get in there proper
     
  3. N_Cook

    N_Cook Guest

    Got into that panel now
    Although no observable damage to that trace, I may as well run a line // to
    this trace while in there. Looks like that mod, replace the 2 4p c/o sw ,
    the 2 1/4 in sockets for Insert and at least remove the main slider ,
    probably replace.
    Putting some alternate sets to the pins of the interboard headers, and keep
    fingers crossed.
    After that, should it bounce, I suppose its a matter of building an active
    buffer and LEDs as telltales , half way through the outer stages, to
    localise down a bit.
    I will try and advise the owner to swap to using the upper channels , in
    case its a problem earlier on.
     
  4. N_Cook

    N_Cook Guest

    Force on the 0.25 socket L insert sw about 700gm, to break contact, about
    1400 gm on the R to break contact is a bit suspicious. Normally I would
    expect problems in the order of 300 or 400 gram contact force. Found a pair
    of 4w c/o switches to fit in the 13.5mm of clearance space.
     
  5. N_Cook

    N_Cook Guest

    To desolder the 4p c/o switches you need to sling .6mm wire under the sw
    body and pulling when desoldering. Normal clamp force over the body is
    enough to break-up the casing of these very weak switches. At least I could
    see inside and no wonder they're problematic.
     
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