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microwave microswitch

Discussion in 'Electronic Repair' started by [email protected], Dec 30, 2013.

  1. Guest

    Hi Gents, Well the microwave stopped working over the holiday.
    (Two year old Cuisinart)
    (Insert rant here about security screws.. torx with the pin in the center.)
    After opening it up I found that the main door micro switch was no good. The warning on the inside says to only replace with other KW3A switches. Here’s a picture of what it looks like.

    http://www.made-in-china.com/showro...ailcMCmWhZrZGYo/China-Micro-Switch-KW3A-.html

    125V, 16A. Only has NO contact populated.

    I’m looking for some place to order this is the US. There are similar looking switches made by honeywell and sold by mouser or newark.
    These are V7 series. V7-6c17d8 14 ozf of force
    or V7-1c17d8 5.6 ozf of force.
    (only speced to 15 amps.. but should be fine.)
    I figure I should order a handful of them since there are *three* switches in the door.
    So first what’s an ozf? is it an ounce? I guess I can pull one of the working switches and measure how much force it takes to close it.

    Here’s a link to newark.
    http://www.newark.com/honeywell-s-c...t/dp/39B3001?MER=PPSO_N_C_EverywhereElse_None

    any other advise is welcome.
    (Hey I'm still searching for specs on the KW3A switch... like life time andcontact force.)

    George H.
     
  2. N_Cook

    N_Cook Guest

    seems to go back to the days of slugs, ergs and all that antedeluvian
    stuff. Like pound-force, presumably ounce-force
     
  3. Guest

    *People's Shining Microwave Factory #7 with a Cuisinart sticker on it.

    Standard warning: There can be enough juice in the big capacitor to zap
    you dead, even if the oven is unplugged. There's also a lot of RF
    floating around, sharp edges, etc. Be careful.
    http://www.repairfaq.org/sam/micfaq.htm#micsaf
    For household stuff, Hazard Fraught Tool's $6 security bit set comes
    in pretty handy. Not what you'd use for production, but fine if you
    need it a couple of times a month. Chain hardware stores like Ace
    and True Value tend to carry this same set as well.
    http://www.harborfreight.com/33-piece-security-bit-set-68459.html
    There are usually three microswitches. One of them opens the 120 V
    line from the wall, like you would expect. One of them switches a
    low-voltage circuit to the control board. One of them *shorts* the
    120 V line on purpose, blowing the fuse in the microwave, if the other
    switches operate in the wrong order. So... check the main fuse as
    well. Also look at the plastic assembly that interfaces between the
    door latch prongs, the door open button (if equipped), and the
    microswitches; if this plastic cracks or gets bent, it can either push
    too hard on the switches or not push them at all.
    They may not all be exactly the same. Sometimes the one that goes to
    the logic board has both NC and NO contacts.
    Ounce force. (As distinguished from ounce mass.) 1 ozf is about
    0.278 N . http://en.wikipedia.org/wiki/Ounce#Ounce-force
    Ten minutes longer than the warranty on the microwave. :)
    This Taiwanese vendor has several flavors of KW3A switch, with a good
    amount of specs on each one:
    http://switchtech.com.tw/upload/201162285428410.pdf

    Standard disclaimers apply: I don't get money or other consideration
    from any companies mentioned.

    Matt Roberds
     
  4. Guest

    Thanks for the nice response Matt. I did short the cap before poking around inside. Once I found the bad switch I shorted the spade lugs and the microwave ran just fine... so no other damage.
    I measured the plunger force last night. ~5 - 6 oz. So I'm going to get some of the honeywell switches. They list a electrical life of 100k operations vs 50k for the specs I found for the KW3A. I was thinking that as well as the average time to failure it'd be nice if they also included the standard deviation. (I guess that's too much to ask.)

    George H.
     
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