• ** REMEMBER! **The microwave can still shock you even unplugged!!

    ALWAYS discharge the high-voltage capacitor first if you even think your hands will come close to any HIGH VOLTAGE components.

    Jeff mentions this: Anything in the high voltage ( magnetron, capacitor, diode, wires to and from ):
    ...Use a metal ( not the shiny chrome type ) screw driver with a insulated handle to short across ( touch both at the same time ) the terminals of the high voltage capacitor to discharge it.

    From Jeff's site: http://www.applianceaid.com/component-testing.php

    Jake

EI30MO45GSA No power - thermal cutoff blown - cause???

arc2v

Premium Member
Joined
Nov 24, 2017
Messages
10
Location
Virginia
Model Number
EI30MO45GSA
Brand
Electrolux
Age
6-10 years
Hi all,
Microwave stopped working. Nothing, no panel or lights. Breaker tripped downstairs, but after resetting panel did not work. Tried new outlet and microwave still didn't work at all.

Cracked her open and found the main thermal fuse was blown. 20A, 150C one right above the magnetron. Curious, I opened the case and verified the ceramic fuse inside was blown. There were some signs of scorching or cabon on the spade tabs, but not inside and the spade wire ends actually look good. A few weeks ago, the light went out but we just thought that was a blown bulb, but upon inspection the bulb looks fine and was just loose in the socket (maybe?). Probably not relevant.

The 15A thermal fuse on the other side of the case is intact; which is weird since if it was an overcurrent situation, you would think the 15A would blow before the 20A.

Nothing else looks amiss. Fan spun freely, wires routed well, no signs of charring, no magic smoke odor. I have no idea what a bad magnetron would look or measure like but the unit heated just fine until going dark.

So I might be able to fix it with a $40 thermal fuse part, but that worries me since there might be an underlying cause I have not addressed.

Any idea what else to check? I may short the fuse there to check other functionality since the other 15A fuse should protect the wiring but I need to know what to look for.

Thanks,
Anthony
 

arc2v

Premium Member
Joined
Nov 24, 2017
Messages
10
Location
Virginia
Update:
Shorted the wires to the fuse and she lit up when plugged in. Keypad looks good and the interior light works when the door is opened (and off when shut).

I did not have the nerve to fire up the magnetron with the case off (and still not knowing what voltages or such to check for.
 

arc2v

Premium Member
Joined
Nov 24, 2017
Messages
10
Location
Virginia
Update 2:
Magnetron at 0.9 Ohms terminal to terminal and Megaohms/Open from terminal to chassis.

I have an ESR meter and it showed the big capacitor at 1uF, right at what is on the label. ESR at 0.56 Ohms, so it is probably good as well.
 

Jake

Appliance Tech - Admin
Staff member
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Aug 24, 2004
Messages
102,102
Location
McMullen Valley, Arizona

rickgburton

Appliance Tech - Moderator
Staff member
Joined
Jul 11, 2006
Messages
34,687
Location
Murray, Utah 84107, United States
Part of the monitoring circuit is the monitor door switch, also called the deadman switch. It's designed to keep the mag tube from operating with the door open so the two wires on the switch, L1 and N are shorted together as long as the door is open. That's the same as plugging a power cord in an outlet and touching the black wire and white wire together, Zap! You probably have a sticky door monitor switch. I've seen this before on Samsung microwaves. In fact Samsung sells the monitor switch and thermal fuse together. Always check all the door switches with a meter by opening and closing the door.
Micro Switch 5304468224
Micro-Switch-5304468224--01079100.jpg
 

arc2v

Premium Member
Joined
Nov 24, 2017
Messages
10
Location
Virginia
Okay, been staring at this for a while this morning.

I think you are right about the cause but wrong about which switch. I identified the Deadman switch as the only one that is vertical. It is operating normally and its wiring tabs look good. Based on tracing the wires, it only sees hot when the control board relay goes hot AND another door relay (bottom, outside) is closed. The other side the deadman switch goes directly to the power board neutral. There are two more swtiches, one that goes to a low voltage part of the control board and another that seems to enable the cooling fan and platter rotation motor (if other control and door relays are enabled).

The door relay I mentioned (lower, outside position) was toast. It is permanently off, but also has liquid plastic on one of the tabs and scorch marks. Based on what should be normal operation, pushing the button should open this switch a full half second before the door opens and closes the deadman switch. If this switch stayed stuck for a moment then the deadman switch did its job and the high current hit both switches, the two fuses, and the circuit breaker. After melting, the door switch must have failed open??? Best I can figure since it's open now and that's the "safe" condition.

Now why only one fuse blew, one switch melted, and the circuit breaker tripped are up for debate.

Thanks for the help. You guys linked to two different sites -- either one affiliated with you? Prices were about the same but I never pass up a chance to pay for good help. :) Thanks again.
 

rickgburton

Appliance Tech - Moderator
Staff member
Joined
Jul 11, 2006
Messages
34,687
Location
Murray, Utah 84107, United States
Unfortunately I don't have a wire diagram for that model so I'm just going by past experience with that model. Both sites are good.
 

arc2v

Premium Member
Joined
Nov 24, 2017
Messages
10
Location
Virginia
Well you got me on the right track. I had no idea the "safety" was to crowbar the mains together to blow the fuse/breaker. Once I read that and looked at the wiring again, it all made sense. So thanks for that!

I'll get the parts ordered today and let you know how it goes. Thanks again.
 
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