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scuba505 02-06-2013 07:06 AM

Micro runs but no heat
I have a microwave that runs fine but will not heat.
  1. I tested all the micro switches and they are functioning correctly.
  2. I tested the 2 internal 20 amp fuses and their ok.
  3. I tested HV fuse on magnatron, tests ok.
  4. I tested the HV Diode with the 9 volt battery trick and it is fuctioning fine. I did replace it anyway because it was so cheap but it did not help.
  5. I tested the HV Capacitor and it is not shorted to ground and when you connect an ohm meter across the leads it reads ohms then gradually goes towards infinity, seems ok.
  6. I tested the magnatron and there are no shorts to ground and across the two terminals its .2 ohms, seems ok.
  7. I check to see if the HV transformer was getting 120v power when the microwave was plug in and it is on the black.
  8. I tested the HV transformer by ohming it out with the specs given but its a little confussing. I know what the primary and secondary winding are but what wires should I test? There is blue/white, black filament and two reds and white to the magnatron/capacitor.
  9. Lastly in following the schematic I noticed the two secondary relays on the control board. The neutral wire passing through both relays is tied into the door safetys and other controls but in testing, relay #1 does not seem to close allowing the neutral circuit to complete to power the HV transformer. What do you think?

Simon / APP Team 02-06-2013 01:11 PM


Remove the plug from the transformer's primary winding and check if there is 120VAC with the MW turned on.If you have correct voltage - replace the magnetron (it lost the vacuum) Part number: W10126786

Part number: W10126786

If not - there is the problem with the control board.

Here are the breakdown diagrams and 03-Interior and Ventilation Parts parts for Maytag MMV4203DS00 -

Post the results.


scuba505 02-06-2013 06:17 PM

Replaced the magnetron and it's working again.

Simon / APP Team 02-07-2013 11:42 AM

You are welcome.


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