Repair guides
Pick a type, an appliance or a brand. Every guide lists the tools, the safety call-outs, the steps and the reading you should expect.
Diagnostic · 374
Symptom → most likely cause, step by step
Component tests · 69
How to test a specific part, with expected readings
Installation · 33
Install, replace and hook up appliances correctly
Fundamentals · 24
Core skills every appliance tech uses
Appliance
Brand-specific guides
25 guides · Microwaves
Diagnostic · 20
Guide · MicrowaveMicrowave dead, no display or power
Rule out the outlet and breaker/GFCI first. Inside, the usual cause is a blown line (main) fuse, often blown on purpose by the monitor switch when a door switch fails, so test the door switches before replacing the fuse. Thermal cutoffs and the control board are next. Internal work is high voltage: trained techs only.
Guide · MicrowaveMicrowave door won't close, won't open or latch broken
Obstructions, an unlevel install or soil on the contact area cause most closing problems. Broken latch hooks, door release levers or switch actuators need parts and HV-safe disassembly.
Guide · MicrowaveMicrowave drawer will not open, close or stay closed
Rule out an obstruction, an overloaded drawer, the control lock and a power interruption, then reset at the breaker. Persistent faults point to the position/sensing switch, drawer motor, slides or the control; check for oversized mounting screws on new installs.
Guide · MicrowaveMicrowave has display/clock but won't start
Rule out user settings first (control lock, demo mode, Start not pressed, shipping spacer). If those are fine, the control is not seeing a closed door or is not driving its relays: door switches, latch, or control board.
Guide · MicrowaveMicrowave heats slowly or weakly
Confirm with a water test on High. Then rule out a low power setting and low line voltage, since a small voltage drop cuts output a lot. An aging magnetron is the most common part cause; poor connections and a failing thermal protector also show up.
Guide · MicrowaveMicrowave hums loudly (with weak or no heat)
A loud hum is usually the HV transformer under heavy load from a shorted HV diode, a shorted magnetron or a failing transformer. All checks are in the high-voltage section.
Guide · MicrowaveMicrowave keeps blowing the line fuse when the door is opened or closed
The monitor switch is designed to short the line and blow the fuse if the door switches do not open in the right order. Worn latches, a misaligned door or a failed switch cause this. Replace the failed switch(es), check latch alignment, then replace the fuse with the exact rating.
Guide · MicrowaveMicrowave keypad not responding (or phantom presses)
Rule out control lock first. Then the usual causes are a worn or moisture-damaged membrane keypad or a loose ribbon at the control board. Unplugging the keypad ribbon separates a bad keypad from a bad board. The control board sits next to high-voltage parts on most models.
Guide · MicrowaveMicrowave light stays on (cooktop or cavity light)
Cooktop light: wrong bulb type or a light timer setting are common causes. Cavity light on with door closed points to a door switch not releasing or a stuck relay on the control board.
Guide · MicrowaveMicrowave runs but does not heat
No heat means the high-voltage circuit is not producing microwaves: HV fuse, HV diode, HV capacitor, magnetron, HV transformer, a door switch, or (on inverter models) the inverter board. Every internal test is high-voltage work for trained techs only, with the cord unplugged and the HV capacitor discharged and verified.
Guide · MicrowaveMicrowave shuts off by itself during cooking
Mid-cook shut-downs usually mean a thermal cutout is opening because the cooling fan failed or the vents are blocked, or a marginal door switch is opening. Check airflow and installation first, then the fan, cutouts and switches with the HV capacitor discharged.
Guide · MicrowaveMicrowave sparking or arcing inside
Rule out metal in the cavity first (foil, twist ties, metal-trimmed dishes, a rack on a model not meant for it). The most common part failure is a grease-soaked, carbonized waveguide cover. Chipped cavity paint and a damaged magnetron antenna cap are next. Stop using the unit until fixed, since continued arcing can damage the magnetron.
Guide · MicrowaveMicrowave starts by itself or will not stop
A microwave that heats on its own is a fire hazard: unplug it and do not use it. The usual cause is a stuck relay or shorted triac on the control. On OTR units, a fan that starts by itself is often normal heat protection, and a light that stays on can be moisture.
Guide · MicrowaveMicrowave trips the house breaker or GFCI
Separate a supply problem (shared or undersized circuit, GFCI nuisance trips) from an internal short. Internal shorts in the HV section usually blow the internal fuse; a trip on start can also come from a shorted HV component.
Guide · MicrowaveMicrowave turntable clicking, grinding or jerking
A turntable that reverses direction between cycles is normal. Clicking and grinding usually come from a dirty or damaged roller ring, a worn drive coupler or a tray not seated on the coupler; a failing motor is last.
Guide · MicrowaveMicrowave turntable not turning
Check the easy parts first: tray seating, roller ring and the plastic coupler. If the coupler does not move while cooking, the turntable motor (under the cavity floor) is the likely fault. Motor access is outside the cavity: unplug, and on any model where the cabinet must come off, follow the HV capacitor warning.
Guide · MicrowaveMoisture or condensation on the microwave door
Some condensation is normal with moist or covered foods. Moisture between the glass usually evaporates with the door left open. Persistent heavy moisture on an OTR unit can mean the cooling airflow is restricted.
Guide · MicrowaveOver-the-range microwave vent fan or cooktop light not working
Start with bulbs, grease filters and the fan's thermal protection. A fan that runs by itself is often a stuck relay on the control board or the board's automatic hot-cooktop protection reacting to heat below. Fan motor and relay tests are internal: high-voltage warning applies.
Guide · MicrowaveOver-the-range microwave vents poorly (smoke and steam not captured)
Most cases are installation: the blower was never rotated from the factory recirculate setup, the damper is taped or stuck, or the duct is the wrong size, crushed or too long. Clogged filters and a grease-packed blower wheel are next.
Guide · MicrowaveSensor cook / auto programs not working
Sensor programs depend on a humidity or vapor sensor and a correct load. Most failures are usage (tight covers, tiny loads, hot cavity) or grease on the sensor; a failed sensor or wiring shows a code.
Component tests · 4
Component test · MicrowaveMagnetron: filament and filament-to-case tests (microwave)
The magnetron turns high voltage into microwave energy. An ohmmeter can catch an open filament or a filament shorted to the case, but it cannot prove the tube makes full power. Rule out the HV diode, capacitor and transformer before ordering a magnetron.
Component test · MicrowaveMicrowave high-voltage diode test
The HV diode works with the HV capacitor to double the transformer voltage for the magnetron. It is made of many junctions in series, so an ordinary meter only shows it is not shorted. A shorted diode is a classic cause of no heat with a loud hum.
Component test · MicrowaveMicrowave high-voltage transformer windings
The HV transformer has a primary, a high-voltage secondary and a low-voltage filament winding. Resistance checks find opens and shorts to the core; turn-to-turn shorts may still need a known-good comparison.
Component test · MicrowaveMicrowave HV capacitor and bleeder resistor
The HV capacitor has a built-in bleeder resistor meant to drain its charge, but bleeders fail, so always discharge by hand. A shorted capacitor blows the HV fuse immediately. Resistance tests catch shorts; a capacitance reading is better.
