KitchenAid KBMS1454SSS-3 Microwave stops heating

[jwicklin]

I have a KitchenAid KBMS1454SSS-3 Microwave that stops heating part way through the cook time setting.  The symptoms are that when I place a 32 oz container of water in the unit and set the cooking time for 3 minutes I can hear the magnetron come on and cook for a good bit of the set time.  However at some point (e.g. 20 seconds left on countdown) I hear the magnetron hum stop while the countdown continues.

For purposes of complete awareness of what has been done since I received the unit with the issue here is what I have replaced so far:

• The turntable motor (because it was not turning at all and no continuity between terminals).  I do not believe this is related to the subject issue but mention it in interest of full disclosure
•  The humidity sensor - I was getting no continuity between pins 1 & 3 of the old humidity sensor so I reasoned that a failed humidity sensor could be causing the premature shut off of the magnetron.  This continuity check was listed in the service manual as the way to test the humidity sensor.

Thanks in advance for any assistance you are able to provide.  I am hopeful of identifying the cause prior to purchasing additional components as I would like the next purchase to solve the problem.

Regards,

Joe

[Budget Appliance Repair]

Make sure the cooling fan is running properly and all air guides are in place - sounds like the mag tube maybe overheating and tripping the reset-able thermal cutout on mag tube, (Mag Tube overheating from not being cooled from fan).

When you hear the mag stop making the humming noise can you stop it and put a fresh load of cold water and restart it for another 3 minutes and no heat at all?   Have you timed how long it takes before you can use it again and actually have it heat.

[jwicklin]

Thanks for the response Willie.  I think you are onto it - I put cold water in and set it for 3 minutes - a bit colder ambient temperature today and it almost made it through the 3:00 minute cycle but magnetron stopped humming with 9 seconds left - I opened the door with those 9 seconds still on the timer, put a fresh container of water in and tried a restart and the magnetron did not engage.  I cleared the remaining time and set cook time to 3:00 minutes and the magnetron did not restart.  I also noted the turntable was not spinning during these cycles either.  I pulled the circulation fan to test it and it measures 14 ohms across the terminals.  Control board?  If so, it probably requires board level repairs since this control board does not appear to be available anymore - odd since it is a 2012 unit.