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Help Identify this Diode.

Discussion in 'Troubleshooting and Repair' started by Masa Yama, May 1, 2014.

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  1. Masa Yama

    Masa Yama

    May 1, 2014
    I have been at this for sometime no on and off and can't get an answer from any out there on some other forums about toyota vehicles.

    The part I am trying to fix is a 1980's toyota door buzzer which in fact is a small circuit board. the part in question is what seems to be a small diode. In the image below I have pointed it out as #3. [​IMG]
    This circuit board is the buzzer you find in most cars for your seat belt, key in ignition, etc... This also is connected to the dome light in the car. So when you open the door on the drivers side the light comes on. The passenger side door by passes this so it's working fine.

    I have check continuity to the door switch to the #2 blade on the picture. As well have checked continuity to the dome light from the blade shown as #1 on the picture.

    When the door is opened the switch is grounded and travels to #2 blade on the pic then is sent through the board and bridged over to #2 to the dome light bridge by the diode.

    To better understand that here is the backside of the circuit board for you to see.


    #2 is the in coming from the door switch which is bridge to #1 to the dome via the #3 Diode. #2 is also connected with the rest of the circuit board which controls the buzzer when you leave the keys in the ignition or seat belt unfastened all of which work, but the dome light. I want to repair the bridge #3 which is the diode which bridges #2 to #1. Can anyone tall me what diode this is? the color is a dark brown and a lighter brown ring on the end you can see this on the first picture above. There seems to be some numbers which is hard to make out, but I think it's 271 on it.

    If anyone can help identify this diode possibly a zener diode.
  2. Masa Yama

    Masa Yama

    May 1, 2014
    Okay a little help from some on the toyota forums tells me that his buzzer has a marking B12
  3. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    OK, it sounds like opening the door turns on the buzzer and the dome light.

    And if the dome light is on, the buzzer will also sound, even with the door closed.

    If that is true, the explanation for the diode (3) is to provide that functionality.

    If the diode has failed, then there will be some difference in the door/dome light interaction.

    The diode should show some continuity in one direction, but none in the other.

    A suitable replacement might be a 1N400x (assuming the interior light is under 12W) or a 1N540x for up to 36W. In all cases, the "x" can be any number, a 1N4001, and a 1N5404 are pretty common parts).

    The band on the end indicates the polarity of the diode. A replacement (likely black with a white band) should be oriented with the band at the same end.

    Save the original part -- just in case.
  4. johnbkobb


    Mar 11, 2014
    If it were me I would just un solder it and look for the P/N then replace with the same
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