37
OVEN SYSTEMS
Microwave System
The oven employs left and right microwave
systems. In the case of an over-current situation,
the F3 fuse (20 amp) will blow, shutting off both
systems immediately.
This section contains information about the
following components:
- Capacitors
- Filament transformers
- High-voltage transformers
- High-voltage diodes
- Magnetrons
- Magnetron cooling fans
- Magnetron thermostats
- Relay (K1 - Filament)
- Relay (K2 - Anode)
- Relay (K7 - Encore: Magnetron cooling fans /
Encore 2: All cooling fans)
- Waveguides
This section also contains procedures for:
- Testing a capacitor (page 37)
- Wiring the filament transformers (page 37)
- Wiring the high-voltage transformers (page 38)
- Testing a filament or high-voltage transformer
(page 38)
- Testing a high-voltage diode (page 39)
- Testing a magnetron for an open/shorted
filament (page 40)
For information on accessing and removing parts,
see the Appendix.
Capacitors
- Capacitor rating is 0.91uF, 2500 VDC for all
60 Hz installations (except Japan).
- Capacitor rating is 1.15uF, 2500 VDC for all
50 Hz installations.
- Capacitor rating is 0.85uF, 2500 VDC for
60 Hz Japan installations.
Testing a Capacitor
DANGER: Never attempt any measurement
of the capacitors while they are enabled.
Lethal voltage will be present. Measure only
in compliance with these procedures.
1. Disconnect the oven from the power source.
2. Fully discharge the capacitor.
3. Isolate the capacitor from the circuit.
4. Check for an open or shorted capacitor by
placing ohmmeter leads between the capacitor
terminals:
- Escalating ohm readings = capacitor OK
- Constant infinite resistance = capacitor open
- Constant very low resistance = capacitor
shorted
5. If the capacitor is not open or shorted, set the
meter to measure capacitance and again place
the leads between the capacitor terminals. The
meter reading should equal the label value, plus
or minus 10%. If not, replace the capacitor.
Filament Transformers
For better operation and reliability, the oven
utilizes separate transformers in order to preheat
the magnetron filament.
The filament transformers are energized for
approximately five seconds prior to energizing the
microwave circuit via the high-voltage transformers.
When in operation, the filament transformers
supply approximately 3.15 VAC at 10 amps to each
magnetron filament. The filament transformers are
controlled via the K1 relay.
Wiring the Filament Transformers
The installation of filament transformers is straight-
forward. Filament transformers are wired in-phase
and in-line. Refer to the schematic detailing proper
wiring (page 64).
To verify correct wiring (North America),
measure the voltages between terminals 1 & 2 and
1 & 3 on FT1 and FT2. The voltages must be 208
and 240 VAC respectively. See the table on page 39
for resistance values.
NOTE: The orange wire always goes to terminal 3
on US models.
To verify correct wiring (International), measure
the voltage between the taps on FT1 and FT2. The
voltage must be 230 VAC. See the table on page 39
for resistance values.
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