LG Microwave F-5 — Magnetron / high-voltage circuit error
LG Microwave · Error code F-5
What F-5 Means
The control detected a fault in the high-voltage path that powers the magnetron (HV transformer, HV capacitor, diode, or magnetron itself). The unit may run but not heat — STOP using it until repaired.
Symptoms
- F-5 on display
- Food not heating
- Loud hum or buzzing during cook cycle
- Burning smell from vent
- Microwave trips the breaker
Common Causes
Open filament or shorted internally — common after 5–10 years of heavy use.
Diode fails closed, dragging the HV capacitor into a dead short.
Internal short or open prevents proper HV waveform.
Primary or secondary winding open/shorted.
Slip-on terminal at magnetron or capacitor has arced and lost contact.
How to Fix It
- STOP using the microwave. The high-voltage section can hold a lethal charge even when unplugged.
- Unplug the unit and let it sit at least 5 minutes; only attempt service if you are trained — otherwise call a technician.
- ALWAYS discharge the HV capacitor with an insulated screwdriver across its terminals before touching anything.
- Inspect for burned spade terminals at the magnetron, HV capacitor, and HV transformer; reseat or replace as needed.
- Test the HV diode with a high-voltage-capable meter (or by substitution); replace if shorted.
- Test the magnetron filament continuity (should be near 0 ohms) and filament-to-case (should be infinite).
- Replace failed components — magnetron, diode, capacitor, or transformer — with exact OEM parts.
- After repair, test with a cup of water for 60 seconds; if F-5 returns, recheck connections or escalate to board-level diagnosis.
Parts You May Need
If diagnosis points to a failed part, these are the common replacements. As an Amazon Associate we earn from qualifying purchases.
More LG Microwave Codes
Verified against manufacturer documentation: lg.com
Always unplug an appliance before servicing it. This guide is for informational purposes and is not a substitute for a qualified technician.