Maytag CMV1000ADW Microwave under cabinet light & fan always on, after bulb replace short circuit

[Wickline]

Model Number

CMV1000ADW

Maytag CMV1000ADW Microwave under cabinet light & fan always on, after bulb replace short circuit

I have a CMV1000ADW over the range microwave that I'm trying to troubleshoot the control board on. Background is that the under cabinet light bulbs were missing and I failed to unplug the microwave before installing new bulbs and inadvertently caused a short circuit. The microwave appeared to be functioning properly other than lack of bulbs before this incident.

I took the control board out and could see that the short circuit had burned a couple of traces on the pcb which I have repaired with jumper splices. I also tested all the capacitors with an ESR meter and replaced all that measured bad. I used a 12V battery to test relays 2, 3, 4, 5, & 6 and verified that all were functioning.

I also checked coil resistance on these same relays and all appear to be within spec tolerances. I checked relay 7 a switching relay and confirmed that it is in the NC position however I have not yet attempted to energize that relay to test for the NO condition. When I reinstalled the board in the microwave the under cabinet lights come on but so does the fan and it is now not possible to turn off either the fan or the under cabinet lights.

I am able to change the speed of the fan between high and low speed but it does not respond to the "off" selection. I currently have the board out of the unit again. Any ideas on what else I should check that is causing this "always on" condition? I did not check door open / door closed condition to see if it had any affect on fan and lights.

I also didn't check to see if turntable was turning and don't recall if internal cabinet light was on or off. The door was closed when I plugged the unit in and observed the fan and under cabinet light "always on" condition. I will upload a copy of the wiring diagram that comes with the unit.

 

[Jake]

Hi,

Rick and Jeff are the microwave experts here, I will see if Rick can help you.

Jake

 

[Wickline]

Thanks Jake - since my posting I have taken the cover off and verified some of the non-board components. Both the bottom TCO and cavity TCO have continuity. The vent thermal switch reads open. I have also removed relay 7 from the board. While it would not trigger with 12V applied it did with 18V and provided continuity from common to the opposite pole from non-energized. I have also verified that all 4 door microswitches are functioning as expected in door open / door closed conditions.

 

[rickgburton]

What exactly shorted when you replaced the bulbs? I probably won't be much help. I can tell you the board is most likely the problem but because it was a short it's possible one or more keylines may be shorted in the touch pad. Unfortunately my expertise ends at the board. PC board schematics for most appliances don't exist. Other members with a background in electronics have repaired boards before. Some have luck and some don't. It's not cost effective for a tech to repair a board so most don't bother with them. That's one of the biggest differences between appliance repair and "online" appliance repair.

 

[Wickline]

Line voltage shorted to the cabinet when trying to disconnect the lead to the bulb socket. It would be nice to have a pin to pin from like a service manual for the keypad to see if there was something in it shorted.

 

[bigbuck]

Was able to come up with this service manual that covers your model and others.Good luck.

 

[Wickline]

BigBuck - thanks loads!!

 

[Wickline]

BigBuck - once again thanks! The service manual had the pin to pin mapping for the keypad ribbon cable / connector and with it I was able to verify that I still have a functioning keypad which seems to isolate the issue to the control board.