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GK fan replacemant, puzzled about DC volts

Discussion in 'Amps [BG]' started by Mad Tango, Jan 22, 2013.

  1. Mad Tango

    Mad Tango

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    I have a GK backline 600 practice amp that the colling fan went out. The orginal fan is 24 volts dc on label. I can find a direct GK replacement fan that also varifies the 24 v DC input voltage for my model. However; when I measure the DC volts at PC board output two pins (W/fan disconnected) it is 60 volts DC. I realize that the fan load/resistance will drop some of the volts when connected, but from 60 to 24volts- thats a big drop needed. I was wondering if the way the amp might have been wired, do I need a 48 VDC fan. Anyone here ever replace a fan?
  2. craig.p

    craig.p

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    Switch your meter to AC volts and measure again. If you get a reading, that may provide a clue as to what's going on.
  3. Mad Tango

    Mad Tango

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    OK, I'll check It will about 5 min to do this.
  4. Mad Tango

    Mad Tango

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    I get 0 volts ac
  5. fdeck

    fdeck Supporting Member

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    It may be 24v under load.
    Still, to be safe, it's best to contact gk.
  6. Mad Tango

    Mad Tango

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    Also, I forgot to mention that now I realize the fan never worked when I bought it about 3 months ago. This is my first GK and I thought it was air cooled because its an entry level GK amp. I noticed it had that hot electronic smell. I had to look closely into the small vents and see the fan inside. I am wondering if the fan got blown up right away w/mismatched voltage.
  7. B-string

    B-string Supporting Member

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    There is a 24Volt zener diode that falls out of circuit with the fan disconnected. 24Vdc fan is correct.
  8. B-string

    B-string Supporting Member

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    The fan is only supposed to come on when needed to lower heat sink temp. It does not run all the time.
  9. Mad Tango

    Mad Tango

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    Thanks for the info. I just ordered a $3.95 fan that fit ALL the requirements besides 24 VDC (size, amp draw, RPM etc.) of the orginal Jamicon fan on E bay so I won't be out much if it doesn't work.
  10. sconix

    sconix Supporting Member

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    The fan is the load off of a variable regulator. The source is 60 volts but there is a 24v zener limiting the output v under load. A temp sensor at the bottom of the circuit varies the ref with temp.
    At least that's what it looks like to me. There maybe a different explanation. The amp calls for a 24vdc 160ma 80x80mm fan. Unless Q28, Q29 the 24v zener or temp sensor are bad, you should be good to go.
  11. Mad Tango

    Mad Tango

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    Thanks to all!!- for the quick and informative responses. The fan by it self reads open ohms, hope it its JUST the fan. Now, I feel better that it does take a 24 volt fan.
  12. fdeck

    fdeck Supporting Member

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    Two or three 9-V batteries in series should be able to run the fan just briefly to see if it works.
  13. two fingers

    two fingers Loud Mouth Know It All Blowhard Gold Supporting Member

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    Doesn't take but a minute or two around here. Awesome.

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