A microwave with a dead light divides into two completely different repairs depending on where the lamp lives. On most over-the-range units the cooktop lamps underneath change from the outside in a couple of minutes, and that is a genuine DIY job. The cavity lamp that lights the inside of the oven is often behind the outer cabinet, next to the high-voltage section, and that one is not. The first job is working out which of those you are dealing with.
Read this first
- The high-voltage capacitor inside a microwave holds a potentially lethal charge even when unplugged. If the lamp is not reachable from an external cover, stop — do not remove the outer cabinet.
- Unplug the microwave or switch off its breaker before touching any lamp or cover.
- Halogen cooktop lamps run extremely hot and must be handled with a cloth or gloves. Skin oil on the glass creates a hot spot that shortens the lamp's life dramatically.
- Fit only the lamp type and wattage specified for your model. An oversized bulb in an enclosed microwave lamp housing is a fire risk.
Step by step
Work out which lamp has actually failed
Over-the-range units usually have two lighting circuits: one or two lamps underneath that light the cooktop, and a separate lamp inside or beside the cavity that comes on when the door opens and while the unit runs. Check both. A cooktop lamp out with a working cavity lamp, or the reverse, tells you the supply and the board are fine and the fault is local to that lamp. Both out at once points at the control board or the supply instead.
Check the light setting before anything else
Cooktop lamps on most over-the-range units have three states — off, night light or low, and full — cycled by a button on the panel or a switch under the front lip. It is very easy to leave one in the night-light position and conclude the bulb has gone. Press through every state and watch. Some models also disable the cooktop light while the microwave is running, which is normal behaviour rather than a fault.
Change the cooktop lamp
Unplug the unit or kill its breaker. On most over-the-range models the cooktop lamp sits behind a small cover on the underside, held by one or two screws, or is reached by dropping the vent grille at the front. Note the exact lamp type before you buy — these are commonly a small halogen or an appliance-rated incandescent, and some newer units use a sealed LED module that is replaced as an assembly. Handle halogen glass with a cloth and never exceed the rated wattage.
Look at the socket, not just the bulb
With the lamp out, look into the socket with a flashlight. Over-the-range lamp sockets sit directly in the steam and grease plume from the cooktop, and the contacts corrode, discolour and lose spring tension. Blackening on the socket or on the base of the old bulb means the joint has been running hot, and fitting a new bulb into a burnt socket simply kills the new bulb. A corroded socket needs replacing, not cleaning.
Find out whether your cavity lamp is externally accessible
This is the decision point of the whole guide. On some models the cavity lamp is behind a small screwed panel on the outside of the cabinet, or is reached from the vent area at the top front, and changing it is genuinely a DIY job. On many others it sits inside the cabinet itself. Check the owner's manual or a parts diagram for your model number. If the documented procedure begins with removing the outer cover, stop there and treat it as professional work.
Check the door switch on a lamp that only fails on the door
If the cavity lamp comes on while the unit runs but not when the door opens, or the other way round, the lamp is fine and one of the door switches is not being made. Note the exact behaviour — including whether the unit still heats normally — and write it down. Do not attempt to adjust or bypass a door switch. Those switches are the containment safety system, and a marginal one is a reason to call a technician rather than a reason to improvise.
Decide whether it is worth a service call
Be pragmatic about the cavity lamp specifically. A microwave that heats correctly, vents correctly and simply has a dark interior is usable, and a countertop unit costs $90 to $250 new against a $120 to $250 service call. On an over-the-range or built-in unit worth $400 to $1,200 to replace, a technician visit for an internal lamp and socket is reasonable, particularly if you are having something else looked at anyway. Cooktop lamps, by contrast, are yours and cost a few dollars.
What this repair costs
Doing it yourself
$5–$25
Hiring a technician
$120–$280
Prices are general estimates for typical US jobs, not quotes. What you actually pay depends on your appliance's brand and age, the part required, your region, and each shop's labour rate. The DIY figure assumes you supply the labour and buy the part yourself.
Parts you may end up buying
| Part | Install | Typical price | Typical lifespan |
|---|---|---|---|
| Turntable Motor | easy | $15–$30 | 8–12 years |
| Door Interlock Switch Set | moderate | $10–$40 | 8–14 years |
| Turntable Coupler and Roller Ring | easy | $8–$30 | 5–10 years |
| Grease and Charcoal Filters | easy | $12–$45 | Grease: wash monthly. Charcoal: 6–12 months |
| Cavity Lamp and Socket | easy | $5–$25 | 3–8 years |
| Vent Fan Motor | moderate | $40–$140 | 8–14 years |
| Control Board or Touchpad | moderate | $50–$220 | 8–14 years |
| Magnetron | advanced | $55–$190 | 8–12 years |
| High-Voltage Diode and Capacitor | advanced | $10–$60 | 8–14 years |
Still not fixed
When to call a pro
Call a technician for any lamp that is not reachable from an external cover. The high-voltage capacitor holds a dangerous charge even with the unit unplugged, and no interior light is worth removing the cabinet for. Call one too if both lamp circuits are dead while the unit otherwise works, which points at the control board rather than the lamps, or if you find a corroded socket that needs replacing on an internal fitting. If a lamp has been flickering, buzzing, or has left a burnt smell or scorch marks around the housing, unplug the unit and have it inspected before using it again.
More microwave guides
- Microwave Runs But Doesn't Heat — What You Can Safely Check15–30 minutes for safe checks
- Microwave Sparking Inside — Stop and Fix It Before Using It Again15–30 minutes
- Microwave Turntable Not Turning — Easy DIY Fix10–40 minutes
- Microwave Door Won't Close or Latch — Stop Using It Until It Is Fixed15–30 minutes for safe checks
- Microwave Keypad Not Responding — What You Can Safely Check15–30 minutes for safe checks
- Over-the-Range Microwave Vent Fan Not Working30–75 minutes
- Microwave Heating Unevenly — Cold Centres, Boiling Edges30–60 minutes
- Microwave Shuts Off Mid-Cycle — Overheating and Interlocks20–45 minutes for safe checks
- Microwave Making a Loud Noise — Match the Sound to the Part20–45 minutes