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Microwave Repair (failed interlock switch)

By on March 13, 2021
bad interlock switch microwave oven






Microwave oven kept blowing fuses and upon opening it was obvious the top interlock switch was no longer working.

Rather than order the cheapest replacements I opted to get some quality units at considerably higher cost due to the claims:

  • “These are built quite a bit more robustly in our opinion”
  • “Quality Item, Will Outlast Original by Years”

as I wanted the repair to last.

Only the top (of three switches) had failed but I replaced both the top and bottom as they were of the same type (normally open) and I could combine shipping; the middle (normally closed) I left.

microwave oven interlock switch

Fast forward a few months and it was blowing fuses again, often when the door was opened after the cooking had completed; made me suspect the middle switch that I had not replaced, but upon inspection it was the top switch again, even though I had invested in a supposedly better made unit.

Opening it up showed that the switch was in good shape internally but that the actuation finger was made of a plastic that had melted where it touches the switch mechanism.

broken microwave oven interlock switch

The fix was interesting in that I then took the actuation fingers from the old cheap switches which seemed to be of a plastic that has a higher melting temperature and used these to replace those in the ‘superior’ switch.

The microwave is now working just fine again and hopefully will now really “outlast the original by years”. Fortunately my Wife is quite patient as I try and figure out what is wrong with broken devices around the house.

andy sheikh anwar

This article was written by Anwar (Andy) Shiekh originally from London, England; he repairs things to help make an income go further and presently teaches Physics in Colorado, U.S.A.

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  1. Albert van Bemmelen

    March 13, 2021 at 3:51 pm

    Interesting to know that they keep trying to sell lower quality parts for higher prices! Thank you for sharing this Anwar (Andy). It would also be interesting to know what firm or manufacturer sold those? This way avoiding buying those lower quality parts too.

  2. Waleed Rishmawi

    March 13, 2021 at 9:33 pm

    I have not encountered any low quality interlock switches and i have been repairing microwave ovens for a long time. I guess it all depends on what brand the device is.. even the interlock switches that I have in the shop are also good quality ones which are usually taken from microwave ovens that the owners do not want to repair due to high cost of repair. have a very good day

  3. Parasuraman S

    March 13, 2021 at 9:57 pm

    Very interesting article! Welcome!

  4. Anwar Y Shiekh

    March 13, 2021 at 10:18 pm

    Perhaps I was unfortunate as the seller seems sincere that the switches are of superior quality and they seem to be working well after the modification. Even the old switches tended to show discoloration on the tabs which indicates a high temperature.

  5. Gary Drumm

    March 13, 2021 at 11:14 pm

    I’ve had times when I ran out of switches and was able to split these in to, and simply clean the contacts inside and reassemble. They are very simple and can be cleaned and reused in an emergency.

  6. Brian Clark

    March 13, 2021 at 11:40 pm

    Interlock switches fail for one reason: opening the door while the oven is cooking. Simple way to avoid interlock switch failure - stop the oven before opening the door. Too many cooks use the door open to stop the microwave, which leads to arcing in the switches and eventual failure. Pressing the keypad "Stop" before opening the door is the proper means of stopping cooking and opening the door.

    The high temperature in the switch isn't from current, but the arc-over flash that occurs when the switch is actuated at full current. Again, stopping oven operation, and then opening the door ensures that high current isn't present in the switch contacts when opening the door.

  7. Anwar Y Shiekh

    March 14, 2021 at 12:02 am

    Yes, I tend to clean the contacts so things keep running while the replacements are on the way. This repair would not be of much interest if it wasn't for the mixing of parts to get things working, and even then only time will really tell if the repair really worked.

  8. Lynn Blakely

    March 16, 2021 at 7:46 am

    Good repair Anwar: Since you are in the US, for parts check"Repair Clinic" on the internet, they have OEM parts. That was a good tip that someone who replied said to stop the oven first then open the door to stop the high current going through the switch.

  9. Yogesh Panchal

    March 16, 2021 at 4:03 pm

    Anwar Y Shiekh,
    Welcome! to the blog.
    In these type of device actuation finger / Knobs are made of Bakelite.
    Keep sharing....

  10. Anwar Y Shiekh

    March 18, 2021 at 8:05 am

    Thank you all for the warm welcome; repair can be a source of great pride.


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