Cooker Hood Repair

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  • Thunderace7
    New Member
    • Jul 2023
    • 8
    • UK
    #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
    • petehall347
      Badcaps Legend
      • Jan 2015
      • 4440
      • United Kingdom
      #2
      Re: Cooker Hood Repair

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

        Comment

        • stj
          Great Sage 齊天大聖
          • Dec 2009
          • 31248
          • Albion
          #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

            • Thunderace7
              New Member
              • Jul 2023
              • 8
              • UK
              #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

                Comment

                • stj
                  Great Sage 齊天大聖
                  • Dec 2009
                  • 31248
                  • Albion
                  #5
                  Re: Cooker Hood Repair

                  clearly the transistor shunts across the buzzer to mute it

                    Comment

                    • R_J
                      Badcaps Legend
                      • Jun 2012
                      • 9607
                      • Canada
                      #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.

                        Comment

                        • Thunderace7
                          New Member
                          • Jul 2023
                          • 8
                          • UK
                          #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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