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Cooker Hood Repair

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    #1

    Cooker Hood Repair

    Hi.
    I've been repairing a cooker hood for my daughter and, although I have got it working, I am puzzled by a couple of things.
    I have attached the circuit diagram I made from studying the PCB. It is a bit rudimentary but it served its purpose.
    There is a buzzer, driven by output P0.0 of the processor, and the circuit seems to be a bit strange. The buzzer seems to be continually powered by 12 volts but is short circuited by the driver transistor. Any idea why this should be? I have checked the PCB several times and this is definitely how it is wired.
    The second thing is the output to the LEDs. One connection is via a relay contact and the other is via a MOSFET. Both the relay and the MOSFET are controlled by the processor. This seems unusual to me, surely one or other would suffice? Maybe the MOSFET is doing some kind of PWM thing but I don't see why it would need a relay as well.
    If anyone could explain why the circuit might be made like this I would be very grateful.
    Thanks,
    Chris.
    Attached Files
    Tags: None
    #2
    Re: Cooker Hood Repair

    looks like you may have drawn it wrongly . are you sure one side of the buzzer is grounded ?

    Comment

      #3
      Re: Cooker Hood Repair

      it makes clever sense
      if the microcontroller is dead for some reason the buzzer will run,
      the mcu mutes it.

      Comment

        #4
        Re: Cooker Hood Repair

        I'm pretty sure I've drawn it correctly. I've attached the pictures of the board, one is reversed to match the other. The buzzer connections are marked in yellow.
        Attached Files

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          #5
          Re: Cooker Hood Repair

          clearly the transistor shunts across the buzzer to mute it

          Comment

            #6
            Re: Cooker Hood Repair

            The buzzer is likely just a simple piezo device, by rapidly shorting it, it will make a sound.
            Seems to be a INGHAi GPC1708AT-5V4000
            Attached Files
            Last edited by R_J; 11-04-2023, 12:47 PM.

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              #7
              Re: Cooker Hood Repair

              So they are rapidly shorting it instead of driving it, must be a reason for this I suppose. I've never actually heard it make a sound, though. I don't know under what conditions it should.
              Its all back together and working fine so I shall stop worrying about it.
              Thanks for all your comments.

              Comment

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