faulty 12vac dimmer/switch: revised

Discussion in 'General Electronics Chat' started by atlantis43, Apr 30, 2014.

  1. atlantis43

    Thread Starter New Member

    Apr 30, 2014
    This is a corrected version of a recently submitted post, which had some errors in description of item:

    I'm having problem with a 12vac halogen lamp rotary dimmer/switch, which does not turn "off", with light returning to partially "on" when switch in "off" position.
    (Sometimes bulb actually turns off, but if I return to lamp later I find that bulb is again lit!)
    Sorry that I can't take a clear picture of this mini-switch, but I've attached the best I can do of the interior of the switch, and I hope that you'll excuse the verbiage----a picture is worth 1000 words :).

    The original switch has 4 terminals, 2 on top, and 2 on bottom , but only 2 wires (one connected to a top terminal marked ‘B’, and the other connected to a bottom terminal ) which connect to another box of electronic circuitry (which connects to 120vac, and also to the bulb itself). There also is a "jumper" wire connected from the other “top” terminal to the other bottom terminal. There are no other identifying markings on the switch.

    I purchased a replacement dimmer unit, but didn't realize that it was for a 120vac bulb, and was therefore unsuitable. It had a similar looking switch/rheostat (with marking B500k), which was solder-mounted to a circuit board by its "top" two and "bottom two terminals.

    When I disassembled the two switches, they both had identical contact assemblies on the bottom unit (see picture), but the actuator facets of the two switches are not identical, so I can't just switch partial assemblies from one to the other. I also can’t see whatever is in the top part of the switches.

    I'll try to help describe what is shown in the attached picture, which is:
    1) a small fixed contact shaped like a small spoon, to which one terminal is connected. This is the smaller shiny object in the picture
    2) a larger half-circular metal contact, with a small pin at one end and a contact knob at the other end. This is the larger shiny object clearly evident in the picture.
    3) a piece of springy metal (seen end-on in the picture, so it is barely visible) which is mounted inside of the above two structures, and
    I guess serves as the on-off switch when moved by the actuator ridges on the knob.

    My Question is:
    What is the “jumper” wire for on this item.
    Is the above-mentioned "jumper" wire on my original switch the thing that converts a potentiometer into a switch-potentiometer? If I were to install such a jumper on the replacement potentiometer, will it have the same effect?
    (I'm assuming that my original unit was also a B500K pot).

    I hope that I've given a clear enough understanding of the problem that someone might be able to provide an answer.
  2. MaxHeadRoom


    Jul 18, 2013
    There is not much point in double posting, and still there is no circuit or picture?