30 OVEN SYSTEMS
Magnetron Thermostats
The magnetron thermostats are “open-on rise.”
They are designed to open at 270
º
F (132
º
C), which
triggers an F5 fault.
NOTE: The magnetron thermostats are wired in
series. If one opens, the control will switch off both
magnetrons until the open thermostat closes. The
thermostats are self-resetting.
Testing a Magnetron for an Open/Shorted
Filament
DANGER: The only safe way to test a
magnetron is by a resistance test of its
filament. Never attempt to measure the
magnetron using any other method while the
microwave system is on. Death or serious
injury will occur.
1. Disconnect the AC power source and discharge
the high-voltage capacitors.
2. Isolate the magnetron from the circuit by
removing the wires from the F and FA terminals
(Figure 41).
3. An ohmmeter connected between the filament
terminals (F, FA) should indicate a reading of less
than 1 Ω (Figure 41).
4. A continuity check between either filament
terminal and the magnetron chassis should
indicate an infinite resistance (open).
CAUTION: Do not allow debris to enter
the waveguides when servicing the
magnetrons.
Relay - K1 Filament
The K1 relay is a 240 VAC, 24 VDC coil, 20 amp,
sealed double-pole, double-throw relay. It switches
power to the filament transformers.
Relay - K2 Anode
The K2 relay is a 240 VAC, 30 amp, double-pole,
double-throw, 24 VDC relay coil. It switches power
to the high-voltage transformers.
Relay - K7 Encore: Magnetron Cooling Fans /
Encore 2: All Cooling Fans
The K7 relay is 240 VAC, 24 VDC coil, 20 amp,
sealed single-pole relay. It switches power to the
magnetron cooling fans when the magnetron
filaments are actuated. Power is switched off after
four minutes and fifteen seconds.
NOTE: The four-minute, fifteen-second timer starts
over each time the magnetron filaments are actuated.
NOTE: In the Encore 2, the magnetron cooling
fans are actuated by the K7 relay when the EC
temperature exceeds 120°F (49°C), regardless of
magnetron operation.
Waveguides
The waveguides channel microwaves into the cook
cavity. If debris or contamination gets into the wave-
guides, the life of the magnetrons may be shortened.
Be careful to not allow debris into the waveguides
when servicing the magnetrons.
Troubleshooting
The following faults may occur in relation to the
microwave system:
- F3: Magnetron Current Low (see page 39)
- F5: Magnetron Over Temperature (see page 40)
The following issues may occur in relation to the
microwave system:
- Electrical component failure (blank or
scrambled display, damaged control board, etc.)
- Food not cooking properly (see page 45)
Filament and High
Voltage Terminals
Antenna
Figure 41: Magnetron Detail
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