• ** 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

Frigidaire Gallery FGMV175QFA trips breaker, humming noice, bad Vent thermal cutoff

sha

Premium Member
Joined
Feb 23, 2019
Messages
3
Location
TEXAS
Model Number
FGMV175QFA
Brand
Frigidaire
Age
1-5 years
Less then 2 year old.

Trips dedicated breaker when open/close door or sometime press start button.
Also making humming sound - while plug in and door already close. (like its cooking - without pressing start)

  • I checked all 3 door switches, working fine. (on door open and close combination 2/1)
  • Fuse working fine.
  • Vent Thermostat cut off part#5304464094 70V (#50) not showing continuity and look bad


I am not technician please advise.

My understanding if thermostat is bad, microwave should not get power.
Do you all problem can related to this bad thermostat ?.
Or replacing it will again below it up.

Thanks in advance
 

rickgburton

Appliance Tech - Moderator
Staff member
Joined
Jul 11, 2006
Messages
34,062
Location
Murray, Utah 84107, United States
Microwave FGMV175QFA Repair Parts

Isolate the problem by separating the HV from supply voltage. Remove the two wires on the primary side of the transformer and tape the ends if necessary. Start the microwave and see if the breaker trips. If not the problem is one of the HV components. If the problem persists with the wires removed, and the door switches are good, the problem is most likely the board.

However, the microwave is tripping a dedicated circuit breaker and not blowing the 20 amp fuse makes me question the circuit breaker.
 

sha

Premium Member
Joined
Feb 23, 2019
Messages
3
Location
TEXAS
Thank you. Sorry for delay.

you mean remove wires from main transformer ? and tape them separately.
Does it worth to replace bad Vent Thermostat cut off, or problem look with something else?.

Yes we have dedicated 20Amp circuit breaker, we call electrician he check circuit. When he plug other high power equipment in the circuit it didn't trip, while when he plug microwave in another circuit it tripped too.
 

rickgburton

Appliance Tech - Moderator
Staff member
Joined
Jul 11, 2006
Messages
34,062
Location
Murray, Utah 84107, United States
That's weird. It sounds like a short somewhere in the microwave. You can replace parts until one fixes it but that will get very expensive very fast. Remove the wires from the thermostat and check each terminal to ground. No continuity, the thermostat is good. Doesn't matter if it's open or closed.
 

rickgburton

Appliance Tech - Moderator
Staff member
Joined
Jul 11, 2006
Messages
34,062
Location
Murray, Utah 84107, United States
I can't say if you should replace it or not until I know what's wrong with it. If you don't have the test equipment or patience or if testing is not your thing it might be best in the long run to replace it. The price of microwaves has come down quite a bit.
 

allen123

Member
Joined
Jun 9, 2019
Messages
3
Location
Houston
I had a similar issue.
Trips dedicated breaker immediately after press start button.
Used a multi-meter to check the followings
  • 3 door switches, 2 have conductivity when door closed and 1 haveconductivity when door is open
  • fuse has conductivity
  • bottom thermostat has conductivity
  • hood thermostat does NOT have conductivity
Is the hood thermostat the problem? Assuming the Microwave can be fixed by replacing the hood thermostat?

Thanks!
 

rickgburton

Appliance Tech - Moderator
Staff member
Joined
Jul 11, 2006
Messages
34,062
Location
Murray, Utah 84107, United States
Depends on what model you have. The hood TCO is probably a normally open thermostat It closes at a set temperature to automatically turn on the fan. Primary Door switch, Secondary Door switch and Monitor switch. Which one has Continuity when the door is closed? Did you check them by opening and closing the door?
 
Last edited:

allen123

Member
Joined
Jun 9, 2019
Messages
3
Location
Houston
Thanks, Rick. The Model I have is FFMV164LSA.

I checked the switches again based on your guidance. Looks like all three switches have conductivity when door is closed.

Both primary and secondary switches have conductivity when door is closed, no conductivity when door is open.

The monitor switch has conductivity no matter door is open or closed. Seems like the monitor switch also broken...
 

allen123

Member
Joined
Jun 9, 2019
Messages
3
Location
Houston
Thanks, Rick. This is SUPER helpful! Will order one online and replace it.
One last question, should I also replace the hood thermostat, which doesn't have conductivity? Or that's normal for the hood thermostat?
Thanks!
 

rickgburton

Appliance Tech - Moderator
Staff member
Joined
Jul 11, 2006
Messages
34,062
Location
Murray, Utah 84107, United States
I don't like it when people correct me but I'm going to do it anyways. ;) The correct term is Continuity
Continuity- uninterrupted connection, the state or quality of being continuous
Conductivity- the rate at which heat passes through a specified material
 
Top