LG · Microwave Serious
F-5 — Magnetron / high-voltage circuit error
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.
- Keep using it?
- Limited use only
- DIY difficulty
- Hard
- Verified against
- lg.com ↗
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.
Why it happens
Typical signs: F-5 on display · Food not heating · Loud hum or buzzing during cook cycle · Burning smell from vent · Microwave trips the breaker
- Failed magnetron Open filament or shorted internally — common after 5–10 years of heavy use.
- Shorted HV diode Diode fails closed, dragging the HV capacitor into a dead short.
- Bad HV capacitor Internal short or open prevents proper HV waveform.
- HV transformer failure Primary or secondary winding open/shorted.
- Wiring connection burned Slip-on terminal at magnetron or capacitor has arced and lost contact.
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
Always unplug an appliance before servicing it. This guide is for informational purposes and is not a substitute for a qualified technician. Verified against manufacturer documentation: lg.com.