Gallien Krueger MB150S, Spare Parts Source? (SMPS Board)

Discussion in 'Amps and Cabs [BG]' started by Sub Four, Jul 29, 2016.

  1. Sub Four

    Sub Four

    Jul 19, 2016
    Berlin, Germany

    the switching mode power supply on my GK MB150S is broken. GK sent me the schematcs and i traced it down to the transformer primary winding insulation which is gone, killing the the two switching MOSFETs in front and blowing the fuse as consequence. This is the early MB150S with the first switching power supply 206-0071.

    So i would either need a new transformer T533 (C60-0025-02 BMI G525) or a new SPMS board 206-0071. GK said that the amp is obsolete so no parts available. Anyone knows a source which still has classic GK spare parts?

  2. Good on GK for sending the schematic.

    If you know the voltages and current required you might be able to find a replacement like a Meanwell SMPS that you can shoehorn in.

    If its the first transformer it may be simple to find a similar replacement. Depends on what specs you can get off the schematic for it.
  3. Sub Four

    Sub Four

    Jul 19, 2016
    Berlin, Germany
    The SMPS is symmetric and supplies +-45V at max 4A and +-22V at max 2.5A so you would end up with four supplies, which probably won't fit into the small space, unfortunately.
    The transformer is quite specific for the SPMS, also due to two additional primary coils for the internal supply, i could probably rebuild/rewind it but it might take two or three rounds to get it right.

    I was kind of hoping that there would be someone having a large store of GK spares where i could buy a transformer or SPMS instead of rebuilding it :)
  4. Francesco_zip


    Jan 4, 2023
    Hi, I am trying to repair the switching with the same problem, but seems that the problem is not the transformer, can you share the schematics and we try to repair it?
  5. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
    Good luck!
  6. bucephylus

    bucephylus Supporting Member

    Aug 18, 2002
    Central Ohio
    Sad to read this. These have been long running, outstanding combos for the bass community. Why GK has been unable to update them is a real head scratcher, given the improvements in Class D power sections. I’m still using an MB150E112; and as far as I’m concerned, there is no substitute for it.

    The current product offered, MB112, is 30% heavier, significantly larger, and has fewer player features. Nothing I would ever have an interest in.
    Last edited: Jan 5, 2023
  7. fdeck

    fdeck Supporting Member Commercial User

    Mar 20, 2004
    Madison WI
    HPF Technology LLC
    As I understand it, the SMPS ran into reliability issues, so GK discontinued the MB150 head and replaced the power supply in the combo version with a conventional one with a power transformer hanging into the speaker box.

    An updated MB150 would just use an IcePower. ;)
    agedhorse likes this.