Microwave System; Capacitors; Testing A Capacitor; Filament Transformers - TurboChef NGO/SOTA Service Manual

Microwave System

The NGO oven employs left and right microwave
systems. In the case of an over-current situation,
the F3 fuse 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
- Stirrer motor and assembly
- Waveguides
This section also contains procedures for:

- Testing a capacitor

- Wiring the filament transformers

- Testing a filament transformer
- Testing a high-voltage diode
- Wiring the high-voltage transformers
- Testing a high-voltage transformer
- Testing a magnetron for an open/shorted
filament
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
uses separate transformers in order to preheat the
magnetron filament.
The control energizes the filament transformers for
approximately five seconds prior to energizing the
microwave circuit via the high-voltage transformers.
When in operation, the filament transformers sup-
ply 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 on page 45,
detailing the proper wiring.
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.
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.
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