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Crate BT1000 problem, blowing fuse

Discussion in 'Troubleshooting and Repair' started by Mr. Jussi, Jun 20, 2018.

  1. Mr. Jussi

    Mr. Jussi

    8
    0
    Jun 20, 2018
    Hi,
    I have a crate BT1000 Bass amplifier. I'm in need of schematic for this amp because it blows fuse, so where I could get one?

    I have checked mosfets and they are goners. There is a op amp, ne5532, just before the power stage and I'm measuring with my multimeter continuous -15,3 V out of pin 7. The circuit of crate BT100 power amp section is almost similar. Can someone help?
     

    Attached Files:

  2. Mr. Jussi

    Mr. Jussi

    8
    0
    Jun 20, 2018
    More information: On BT1000 the pin order in NE5532 is different so that 1 2 3 are 5 6 7. Also I want to know what the circuit that includes Q1 is doing - is it continuosly on?
     
  3. Mr. Jussi

    Mr. Jussi

    8
    0
    Jun 20, 2018
    So I got help from a finnish dicussion forum, probably Q1 broke and leaked minus 15.3 volts so that it burned fets. Q1 belongs to a circuit that enables soft start - so no pop sound from the speaker during powering on.

    Just having vacation and will repair the Crate as soon as possible.

    Greetins to everyone from Finland. Be blessed!(I serve in Church with the Crate)

    Believer of Jesus
    Mr. Jussi Rautanen
     
  4. duke37

    duke37

    5,199
    710
    Jan 9, 2011
    Unplug the power amplifier and run the rest through a lamp limiter to protect the main fuse. Check for correct voltages.
     
    Mr. Jussi likes this.
  5. Mr. Jussi

    Mr. Jussi

    8
    0
    Jun 20, 2018
    Hi,
    thanks for the advice. I already tested with unplugging power amplifier. Fuse did not burn and I measured voltages with my digital multimeter. Op amp(the one that is just before the power amplifier) is giving 15.3V out of pin 7 continuously. Just before this op amp is a send and return path. I took my bass signal out from send jack to my
    Zoom pedal and listened with headphones - it was good, everything worked well.

    So only the part of the circuit that includes op amp NE5532, FET J112 and few other components is in malfunction condition.
     
  6. Mr. Jussi

    Mr. Jussi

    8
    0
    Jun 20, 2018
  7. Mr. Jussi

    Mr. Jussi

    8
    0
    Jun 20, 2018
    Hi, in case somebody is interested I fixed my Crate Bt1000 amplifier. So I did not get any address what was the cause for the power amp mosfets to burn. I measured the parts that I thought could be in reason causing damage.

    I noticed that in the power supply the 15 Volt Zener diodes were only 500mW(1N4744). The resistor is 220 ohms in front of that Zener. Voltage drop should be from 40V to 15V. So it is about 114mA current needed to drop 25V to get 15V for the op amp. This is of course too much for 500mW Zener diode(Datasheet 61mA max Zener current).

    When I measured the Voltage of the OP amps crawled up to + - 17V and more. I changed these Zeners to bigger ones (5W/15V 1N5352B). I also changed the resistors from 5W to 7W and now there is more room around the resistors to cool down. PCB under the 5W resistors had marks of too much heat(little bit toasted). Under the final OP amp, before the power amp, I but an IC socket and I changed that IC (Ne5532) to a new one.

    It was a little difficult to find new matching mosfets IRFP9140 and IRFP140. I found IRFP9140 and on the place of IRFP140 I bought IRFPC50. After been using it few times in rehearsals and one time in a gig. I'm happy - it is working fine. Also a little bit less hiss.

    So everyone comments?

    P.S.

    A picture of the parts I changed.
     

    Attached Files:

  8. VenomBallistics

    VenomBallistics

    72
    26
    Aug 30, 2018
    I blew up a lot of amps with a B.C. Rich Warlock. repaired em and retired after the third failure.
    Then, I built the replacements from the ground up.
     
    Mr. Jussi likes this.
  9. Mr. Jussi

    Mr. Jussi

    8
    0
    Jun 20, 2018
    In the above I meant measuring supply Voltage.
     
  10. Mr. Jussi

    Mr. Jussi

    8
    0
    Jun 20, 2018
    Crate working fine still now, when having little free time, studying the little capacitors around the amplifier board wondering what kind of ceramic caps they are. EDIT: In the attached files you can see six of them. Wondering if they are multilayer.
     

    Attached Files:

    Last edited: Apr 30, 2019
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