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Jon
Jon, Appliance Technician
Category: Appliance
Satisfied Customers: 3475
Experience:  Appliance Service Technician with 10+ years experience.
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inverter in microwave keeps going bad

Customer Question

inverter in microwave keeps going bad
Submitted: 1 year ago.
Category: Appliance
Expert:  Jon replied 1 year ago.

Jon :

hello

Jon :

i would first make sure the polarity to the outlet the machine is plugged into is good and is not reversed. that is the number one cause for the inverter to blow out

Jon :

check that and if it is good then you have a shorted wire somewhere in the machine. And unfortunately it may not be found but please try taking it down and appart and check it out.

Jon :

get back to me here if you need more help.

Jon :

i see this a lot. and 90% of the time the wiring or outlet is the problem. so if you have a meter or tester, test that first. and if that i snot your problem please come back here and let me know and I will help you more.

Jon :

And if you feel that i have helped to answer your questions please remember to rate my performance positively below with ok service or better rating. And if you feel that i have not helped you enough, please dont rate negatively. just respond back to me here and I will help you more until you are completely satisfied and we can find and solve the problem.

Customer :

I have taken the microwave down and I have been working on it in my basement. I checked the polarity and Im getting 123 volts through the outlet. In addition my house was hit by lightning 2 months ago and I already had to fix my dishwasher(replaced) and washer(repaired). The microwave showed no symptoms and worked fine till now. The code f-9 came on and i took it down and took it apart. The inverter board was fried, it had turned brownish. I replaced it and it was working but buzzing and overheating. Which it buzzed right before it went out the first time. Next thought was maybe the magnetron was going out, so i replaced it. I can get a wiring diagram for the microwave if that would help. But most of the connections in the microwave are dummy proof, considering their all different and can only go where their supposed to. The exception to this is the noise filter, which seems to be where the power cord goes first and is dispersed from there. Could it be a bad control board( the one with the buttons on it)? Or a bad noise filter board? After looking at the wire diagram the juice is dispersed from the noise filter. Also, the exhaust fan and the lights work fine and as intended. So I think it is within the heating section of the micrrowave. Any suggestions?

Jon :

Hello again,

Jon :

the f9 error is for a bad inverter board. which you already know.

Jon :

there are many reasons for the inverter board to fail including but not limited to a bad thermostat, computer, magnetron, diode, and transformer.

Jon :

i can tell you this, if the machine is heating the low voltage side of the microwave is good.

Jon :

and if the inverter board is continually failing you should start by checking the high side of the microwave. which is the magnetron, capacitor, diode, transformer and thermostats.

Jon :

if the inverter board is failing again and you have already changed the mag and inverter it seems to me like the transformer and capacitor has been damaged by the lightning strike or power outage. and that would send improper voltage to the capacitor and transformer which would burn out the inverter board.

Jon :

I must first say that it is extremely dangerous working on microwaves if you are not sure of what you are doing, especially if you have never checked a microwave before like this, please leave this to a professional.

Jon :

even when the micro is unplugged, the cap will still hold a charge of a few thousands volts. and THAT COULD HARM AND EVEN KILL YOU!

Jon :

so please discharge the cap before doing anything else with this machine.

Jon :

then follow the checks outlined in the website below. it will list how to check several components to your microwave.

Jon :

please just copy and paste the link below to your browser to open and view.

Jon :

http://www.appliance-repair-it.com/microwave-repair.html

Jon :

please focus on the high voltage side of the micro and check the mag, diode, cap and transformer.

Jon :

if you have any other questions please come back to me here and i will help you more.

Jon :

please let me know how you make out.

Jon :

thanks

Customer :

I checked the thermostat, according to the manufacturer it should be sitting at 0ohms and it is. I also checked the wiring for any miswiring, or shorts. On the diagnosis sheet that came with the microwave, which was inside it, it said check inverter, if it keeps going bad check the thermostat. If thermostat is reading 0 ohms it should be good and to replace the control assembly board, which has the transformer on it. As far as the diode goes, I would take a guess and say it is also on the control board.

Customer :

And to further answer your statement, this is my first attempt on a microwave, and I am aware of it being able to hold charge, so I do where rubber gloves when working on it, and I always discharge the electricity off of the machine. Can never be too careful.

Jon :

yes. you can never be too careful.

Jon :

the transformer i was referring to is actually a separate part in the microwave. it is not on the computer board. but yes, what you are following is the tech sheet and work flow chart for the voltage in your microwave.

Jon :

if i may ask, how did you check the wiring for any shorts?

Jon :

and the diode is a separate part as well. forgot to mention that above with the transformer. it is inline with the capacitor. it is the piece of metal that gets hooked up to one of the terminals of the capacitor and gets screwed to chassis ground. that too would need to be checked before knowing if the computer board is your problem.

Jon :

all i am saying here is that you must first check these parts before just simply saying the computer board is the problem. I would hate to see you spend more then $150 on a computer if it doesnt fix your problem.

Jon :

and yes, most times when you have this complaint, the computer is usually the problem. and is sending too much voltage to the inverter board causing it to constantly fail.

Jon :

please get back to me here with the full model number of the microwave so i can look up the part info for you. so if you would like to change the parts yourself you can do so.

Jon :

thanks

Customer : I will get it tomorrow
Jon :

you got it. please do and let me know.

Jon :

this way i will look up the model info and get the part info for you

Jon :

talk to you tomorrow

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