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Behringer UB2442FX Mixer Schematic/voltages Needed

Discussion in 'Electronic Repair' started by Jake Joseph, Mar 5, 2004.

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  1. Jake Joseph

    Jake Joseph Guest

    I have a Behringer UB2442FX Eurorack mixer. Before the flames start,
    I liked it, when it was working. It did exactly what I needed.

    It died, out of warranty, and the switching power supply looks to be
    toasty. Behringer US doesn't have PS modules yet, so it looks like
    board level repair is where it's at.

    It uses very close to a demo circuit from Power Integrations from
    their TOP245Y chip. However, I don't know what the final voltages are
    other than there should be a +5V (Based on the 7805 regulator) and
    there should be a 48V. There are 5 voltages available, guessing from
    the connector.

    ANyone help out with at least the voltages coming out of this
    doohickey would be appreciated. Any other help would also be


    Jake Joseph
  2. Scott Dorsey

    Scott Dorsey Guest

    I'd guess a +15V and a -15V. Maybe a little higher, but probably not
    much higher than that.

    If it's a switching supply, my guess is that the regulation is probably
    done using the 5V line as a reference. If it were done properly, they'd
    be using the difference between the +15V and -15V rails as as reference,
  3. Lord Valve

    Lord Valve Guest

    Almost always +/-15VDC. What are the rated voltages on the caps?
    Most of that Chinese stuff uses 16V caps on the rails.

  4. Jake Joseph

    Jake Joseph Guest

    Well, you are right about the 5V - it gets its reference off of the 5V
    - shoots this through a TL431 regulator.

    I'm guessing that either the switcher has gone bad or the optoisolator
    xsistor has gone bad...any good way to diagnose?

  5. Pooh Bear

    Pooh Bear Guest

    Interesting. I'm designing around the TOP245Y myself right now.

    I've had a look at that PSU - at least I reckon it's the same one. Might
    even have a record of the voltages.

    Remove the PSU from the mixer. First suggestion - look for a short circuit
    output recifier. Just plug it in and see if it attempts a 'hiccup start'.
    That means a short on the secondary side normally.

    If it doesn't even try starting - suggests the TOP has died. In which case
    check the zener clamp and RC snubber. Even seen a similar Panasonic part
    stop working with a failed diode round the RC snubber - that's all it took
    to fix it.

    Just a couple of ideas.


  6. Simple, quick, common fix; one of the secondary rectifiers is shorted
    (usually Ref #D6), be sure to replace with a 'fast' rectifier (we use
    # HER508).

    (Authorized BEHRINGER Service)
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  7. Scott Dorsey

    Scott Dorsey Guest

    Diode tester function on a multimeter will help you check the switching
    transistor in-circuit. You can do the same with the optoisolator. You
    can't find all possible failures in-circuit but you can find some of them.
    Worst case you pull it out, test the switching transtor with the Hfe function
    on your multimeter and swap out the optoisolator (being sure to put a socket
    on the optoisolator because this will happen again someday).

    Switching supplies are no fun to fix, because you can't get them running
    to do diagnosis. A storage scope can help a lot.

    Don't forget the kickstart circuit either, which is a source of failure in
    a lot of switching supplies.
  8. Pooh Bear

    Pooh Bear Guest

    Not much actually - it's an integrated mosfet and controller in a TO-220 style

    Very unlikley the opto has gone - they only run at a few mA.

    The OP hasn't yet indicated if the supply goes into 'hiccup start' mode - audibly
    detected by 'tick - tick - tick - tick'.

    That's a 99% certain output rectifier short.

    The bias winding on these only supplies a few mA. Worth replacing the 1N4148 just
    in case I suppose.

  9. Jake Joseph

    Jake Joseph Guest

    Thanks to all that helped! I think the secondary diode is bad. Scott
    is right, these sure are not fun to diagnose - I'm used to tube amp
    PS's which are a whole lot easier....

    The fast diode is to cope with the frequency of the switcher - right?
  10. Pooh Bear

    Pooh Bear Guest

    Yes, 'normal diodes' - 1N4004 etc don't switch fast enough to be of any use, so there are high speed equivalents for
    example like UF4004. Also many others. Schottkies are fine but have a limited reverse voltage making then useful only for
    5 and 12 V supplies typically.

  11. Mrhotmark


    Jun 4, 2009
    Behringer UB2442FX-PRO Connectors

    For those interested...

    Behringer UB2442FX-PRO Power Supply Connectors

    Looking at the rear of the power supply there are 3 connectors, a 2-pin, a 6-pin, and another 2-pin. All connectors have a red wire on the rightmost pin.

    The leftmost connector attaches to the 48V phantom power switch. On/Off.

    The center connector from left to right is:
    1. Ground
    2. +5VDC
    3. +48VDC
    4. Ground
    5. -15VDC
    6. +15VDC (red wire)

    The rightmost connector is:
    1. Ground
    2. +12VDC (red) for the BNC lamp connector.

    All replacement parts are available from (TOP245, TIP31C, TIP32C, etc)

    If replacing any diodes, make sure they are high speed diodes.

    When all connections are made, all the grounds will tie together including earth ground.

    My experience with these mixers are that some of the high speed diodes tend to short
    along with the small transistors driving the larger ones. (The larger ones being TIP31C for the positive voltages, TIP32C for the negative). A 2N3904 or 2N3906 SOT-23 transistor will work for a replacement.

    In my opinion this mixer is probably the quietest most bang for the buck mixer, but really needs a better power supply design.

    Hope this helps!

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