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Kelly, Appliance Technician
Category: Appliance
Satisfied Customers: 22896
Experience:  Highly accurate diagnostician with over 30 years experience!
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How to test high voltage transformer, 6 hours, yes...I am

Customer Question

how to test high voltage transformer
JA: I'll do all I can to help. How long have you been dealing with this?
Customer: 6 hours
JA: Do you plan on doing the work yourself?
Customer: yes...I am plumber with some electrical experience...this is for my home
JA: Anything else we should know to help you best?
Customer: i have removed HV transformer & have a vom & want to test to see if it needs replacing....did smell some smoke when we last used the MW
Submitted: 1 year ago.
Category: Appliance
Expert:  Appliance Guru replied 1 year ago.

Hello and thanks for using this service, if you have been waiting do not worry or get upset. I am Appliance Guru an extremely experienced tech on the site and I try to get to as many customers as I can. I just picked up your question now. NOTE it takes time for me to type research and add links so please wait for me to respond back I can only do this so fast. Secondly I am not paid anything until you rate my service good using the STAR RATING LINK at the top of your page, the money is paid to the site not me directly.


The easiest way to see if it is good is actually remove the wires to the magnetron tube and start the unit and run it for 10-20 secs. If it does not smoke or make any bad noises it is fine.

Then discharge the capacitor afterwards and then hook it back up and try it.

All I ask is please use the Star Rating Link at the top of your page before leaving, that is the only way I am paid anything through the site and that will also get you a DIRECT LINK emailed to you to get back to me! are greatly appreciated so thank you very much for using this service. If you have any other questions just post back to me here anytime!

Customer: replied 1 year ago.
i have the hv transformer out of a build in MW in the unit was a piece of paper that said to test the ohms for the primary windinng..where do i put the leads from my VOM...also said to test ohms for the secondary winding where do i put the leads from my VOM..thanks
Customer: replied 1 year ago.
wow 24 hrs....that is a long time
Expert:  Kelly replied 1 year ago.

Hi, welcome to Just Answer. Sorry to hear you are having appliance trouble, I know how frustrating that can be! My name is ***** ***** I look forward to helping you!

See the picture at the link below and test with the instructions below.


  1. With an ohmmeter set to the lowest resistance scale, R X 1, measure the resistance from the high-voltage terminal to the transformer chassis (ground).
    1. Some early models are equipped with two or three high-voltage taps. If this is the case, perform the measurement from each tap to chassis ground.
  2. The meter should read about 55 to 70 ohms, depending on which high-voltage tap is being measured and the model being tested.
    1. A substantially higher or lower reading would indicate that the transformer is defective.
  3. Carefully disconnect the leads from the primary (input) terminals
  4. Measure from one transformer primary terminal to the other for a normal reading of less than 1 ohm (i.e., .22 ohms)
    1. A substantially higher reading would indicate that the primary winding is open.
  5. Set the meter to its highest resistance scale and check from each transformer primary terminal to the transformer chassis (ground) for a normal reading of infinity (open circuit).
    1. Any measurement of resistance would indicate some degree of a short to ground
  6. Set the meter back to its lowest resistance scale. Then carefully disconnect the filament leads and measure from one filament terminal to the other for a normal resistance of less than 1 ohm.
  7. Set the meter to its highest scale and measure from each filament terminal to chassis ground for a normal reading of infinity (open circuit).
    1. Any measurement that is substantially different from the normal readings would indicate a defective transformer.