Sunday, December 18, 2011

A Rotary Switch Repair

The style of switch-fitted light bulb socket pictured below is widely used in articulated desk lamps and the like.

This one has gotten stuck 'on', and doesn't want to switch off. These switches often respond well to a bit of reconditioning. The worst part of the job is usually getting the lamp's line cord slackened off so you can get at the thing.

Undoing two small threading screws gets you access to the switch's innards, like so.

The slot in the end of the knob engages and turns a rod that shorts two contacts to turn the light on. The spring keeps the rod firmly pressed down.

Here's a view of the rod inside and the contacts it works with.

[I've already cleaned up the inside parts.]

The switch is shown in its 'on' state -- the rod is bridging two contact 'ramps'. Ninety degrees of CW rotation of the knob will cause the rod to climb the contact ramps, and then it will fall across two insulator ramps and be in its 'off' state.

The contact ramps can be scraped clean with a jeweller's screwdriver. The rod can be chucked in a portable drill and burnished with synthetic steel wool. Blow out any dust, reassemble, lubricate it with WD-40 and it should be back in business.

This switch worked fine once it was back together. I'm actually a bit mystified that it was so stuck; I really didn't see a reason for it when I opened it up.

Anyway, it's working, and it looks to me like it should be trouble-free for a long time.

# # #


# # #

3 comments:

  1. I had the same sticking problem with one of these and had no idea how the switch worked. Was looking for a schematic when I found your post; thanks very much.

    ReplyDelete
    Replies
    1. You're very welcome. 'Glad to have been of help.

      Delete
  2. mine won't turn on. The standoffs are riveted on. looks like it would be more trouble than it is worth to try to fix it?

    ReplyDelete