B&K ref-50 preamp repair

Discussion in 'DIY' started by PF Sound, Jan 10, 2019.

  1. PF Sound

    PF Sound New Member

    Messages:
    18
    Location:
    Pacific NW
    Got another project. Bought this unit (it's a series II) locally for $50 because it won't power on, & I was gonna rob it to fix another series 1 ref-50 that quit on me. Just for bleeps & giggles I decided to try & troubleshoot it. When you push the power button you immediately here a relay click & then nothing happens........no display, no nothing. Seems to go right into protect. But I'm getting power all over the main board at check points. Unplugging boards & ribbon cables yielded no change, & I couldn't see anything that visually looked bad............until........

    038.jpg

    Now, this is on the back side of the tuner board which is a 3rd party unit........not a B&K product, so it doesn't show up on any of the 20+ pages of schematics other than it's part # on the page for for the tuner section of the main board. I googled the part# of the tuner board & came up with nothing. The component that looks smoked is so small that I had a helluva time trying to get a decent picture of it........literally the size of a pencil tip. I'm not equipped to fix a component that small, but I'm curious.........would anyone think that this would cause the whole unit to go into protect?
     

     

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  2. Watthour

    Watthour Electron Rancher - JS3600

  3. PF Sound

    PF Sound New Member

    Messages:
    18
    Location:
    Pacific NW
    I went ahead & cleaned it up......it says 6CW** . I'd like to meter it before assuming it's bad, but, being that it's microscopic, I'm not sure if my mm setting on diode would damage this thing if it wasn't bad.
    I had been using a ref-50 series 1 in my system but one day it just quit outputting through the pre-outs. It fires up up just fine.....everything looks normal, but no output. None of the local repair shops work on these things, & the only place that does is in NY, so when I saw this series II on CL I figured I could salvage some parts to fix mine (they're a modular design). These things are almost identical, save for the DSP board & sw. But this one I just got is in pristine condition......literally looks new, inside & out save for a little dust......so it would be a shame to not a make a little effort to troubleshoot it. Unfortunately, the tuner board isn't modular, & it would be a PITA to try to swap it out.
    Thanks for the reply.
     
  4. stoN_Cold

    stoN_Cold Super Member

    Messages:
    3,433
    Location:
    Belgrade, Serbia
    What is the IC mark?

    [​IMG]
     
  5. PF Sound

    PF Sound New Member

    Messages:
    18
    Location:
    Pacific NW
    LA1875
    4K5
     
  6. stoN_Cold

    stoN_Cold Super Member

    Messages:
    3,433
    Location:
    Belgrade, Serbia
    Can' t find in service manual.
     

     

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  7. PF Sound

    PF Sound New Member

    Messages:
    18
    Location:
    Pacific NW
    Thanks for the effort, ston cold.

    I'm accepting the fact that these units are way above my pay grade. I swapped all the modular boards from the series II unit into my original unit to no avail..........still no output signal. Like I said before, the original powers up fine, goes to standby, then when I hit the standby button it looks to operate normally. It appears as though the processor board from the series II unit is good in that the original unit recognizes it as a sw upgrade, ie goes through a reset & shows the new version on the front display upon initial power up. I tried different inputs, both digital & analog, along with the tuner in case the problem was input related. The specs say the max output signal is 3v..........I'm measuring around 2mv with no change when turning the volume control.
    So now I know both units have problems on the main pcb's............yippee.
     
  8. stoN_Cold

    stoN_Cold Super Member

    Messages:
    3,433
    Location:
    Belgrade, Serbia
    Only?


     
  9. PF Sound

    PF Sound New Member

    Messages:
    18
    Location:
    Pacific NW
    Well, as far as I know.......lol
     

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