Troubleshooting Guide

By sweet_rascal
Rank: Wiz
Rating: 77%, 269 votes

posted on Mar 30, 2008

Problem: Totally dead oven.
Possible causes:
1. No power to outlet (blown fuse or tripped breaker or GFCI).
2. Blown main fuse - likely due to other problems.
3. Open thermal protector or thermal fuse.
4. Defective controller or its power supply.
5. Clock needs to be set before other functions will operate (some models).
Problem: Totally dead oven after repair.
Possible causes:
1. Cabinet screws replaced in incorrect location (safety interlock not engaged).
2. Any number of screwups. :)
Problem: No response to any buttons on touchpad.
Possible causes:
1. Door is not closed (some models).
2. You waited to long (open and close door to wake it up).
3. Controller is confused (pull plug for a minute or two to reset).
4. Defective interlock switches.
5. Faulty controller or its power supply.
6. Touchpad or controller board contaminated by overenthusiastic cleaning.
7. Defective/damaged touchpad.
Problem: Oven runs when door is still open.
Possible causes:
1. Damaged interlock assembly.
2. Cooling fans (only) running due to bad sensor or still warm.
Problem: Oven starts on its own as soon as door is closed.
Possible causes:
1. Defective triac or relay.
2. Controller is confused (pull plug for a minute or two to reset).
3. Defective controller or its power supply.
4. Touchpad or controller board contaminated by overenthusiastic cleaning.
5. Defective/damaged touchpad.
Problem: Oven works but display is blank.
Possible causes:
1. Defective controller or its power supply.
2. Broken display panel.
3. Oven needs to be reset (pull plug for a minute or two to reset).
Problem: Whacked out controller or incorrect operation.
Possible causes:
1. Previous or multipart cook cycle not complete.
2. Controller is confused (pull plug for a minute or two to reset).
3. Defective controller or its power supply.
4. Touchpad or controller board contaminated by overenthusiastic cleaning.
5. Defective/damaged touchpad.
6. Defective sensor (particulalry covection/mirowave combos).
Problem: Erratic behavior.
Possible causes:
1. Previous or multipart cook cycle not complete.
2. Bad connections in controller or microwave generator.
3. Faulty relay - primary (or HV side, much less commonly used).
4. Defective controller or its power supply.
5. Bad contacts/connections on mechanical timers. Intermittent fuse.
6. Power surge at start of cook cycle confusing controller.
7. Microwave (RF) leakage into electronics bay.
Problem: Some keys on the touchpad do not function or perform the wrong action.
Possible causes:
1. Touchpad or controller board contaminated by overenthusiastic cleaning.
2. Defective/damaged touchpad.
3. Controller is confused (pull plug for a minute or two to reset).
4. Faulty controller.
Problem: Microwave oven does not respond to START button.
Possible causes:
1. Defective START button.
2. Faulty interlock switches.
3. Door is not securely closed.
4. Faulty controller.
5. You waited too long - open and close door to wake it up!
Problem: No heat but otherwise normal operation.
Possible causes:
1. Blown fuse in HV transformer primary circuit or HV fuse (if used).
2. Bad connections (particularly to magnetron filament).
3. Open thermal protector or thermal fuse.
4. Open HV capacitor, HV diode, HV transformer, or magnetron filament.
5. Shorted HV diode, HV capacitor (will blow a fuse), or magnetron.
6. Defective HV relay (not commonly used).
Problem: Timer and light work but no heat, cooling fan, or turntable rotation.
Possible causes:
1. Defective (lower) door interlock switch or door not closing fully.
2. Faulty relay or triac.
Problem: Fuse blows when closing or opening door:
Possible causes:
1. Defective door interlock switch(s).
2. Interlock switch knocked out of position.
3. Misaligned door.
Problem: Loud hum and/or burning smell when attempting to cook.
Possible causes:
1. Shorted HV diode, magnetron.
2. Burnt carbonized food in or above oven chamber.
3. Shorted winding in HV transformer.
4. Frayed insulation on HV wiring.
Problem: Arcing in or above oven chamber.
Possible causes:
1. Burnt carbonized food deposits.
2. Exposed sharp metal edges.
Problem: Fuse blows when initiating cook cycle.
Possible causes:
1. Defective interlock switches or misaligned door.
2. Shorted HV capacitor.
3. Shorted HV diode.
4. Shorted magnetron (probably won't blow main fuse but HV fuse if used).
5. Defective triac.
6. Old age or power surges.
7. Defective HV transformer.
8. Short in wiring due to vibration or poor manufacturing.
Problem: Fuse blows when microwave shuts off (during or at end of cook cycle).
Possible causes:
1. Defective triac (doesn't turn off properly).
2. Defective relay.
3. Shorting wires.
Problem: Oven heats on high setting regardless of power setting.
Possible causes:
1. Faulty primary relay or triac or HV relay (not commonly used).
2. Faulty controller.
Problem: Oven immediately starts to cook when door is closed.
Possible causes:
1. Shorted relay or triac.
2. Faulty controller.
Problem: Oven heats but power seems low or erratic.
Possible causes:
1. Low line voltage.
2. Magnetron with low emission.
3. Faulty controller or set for wrong mode.
4. Stirrer (or turntable) not working.
5. Intermittent connections to magnetron filament or elsewhere.
6. Faulty primary relay or triac or HV relay (not commonly used).
Problem: Oven heats but shuts off randomly.
Possible causes:
1. Overheating due to blocked air vents or inoperative cooling fan.
2. Overheating due to bad magnetron.
3. Bad connections in controller or microwave generator.
4. Faulty interlock switch or marginal door alignment.
5. Faulty controller.
6. Overheating due to extremely high line voltage.
7. Stuck stirrer fan resulting hot spots detected by sensors.
Problem: Oven makes (possibly erratic) buzzing noise when heating.
Possible causes:
1. Fan blades hitting support or shroud.
2. Vibrating sheet metal.
3. Vibrating transformer laminations.
4. Turntable or stirrer hitting some debris.
Problem: Oven light does not work.
Possible causes:
1. Burnt out bulb :-).
2. Bad connections.
Problem: Fans or turntables that do not work.
Possible causes:
1. Gummed up lubrication or bad motor bearing(s).
2. Loose or broken belt.
3. Bad motor.
4. Bad thermostat.
5. Bad connections.