TurboChef NGO/SOTA - Microwave System; Capacitors; Testing a Capacitor; Filament Transformers

OVEN SYSTEMS
23
M
icr
owave System
The NGO oven employs left and right microwave
systems. In the case of an over-current situation,
the F3 fuse will blo
w
, shutting off both systems
immediately.
This section contains information about the
follo
wing components:
- Capacitors
- Filament transformers
- High-voltage transformers
- High-voltage diodes
- Magnetrons
- Stirrer motor and assembly
- Waveguides
This section also contains pr
ocedures for:
- Testing a capacitor
- Wiring the filament transformers
- Testing a filament transformer
- Testing a high-voltage diode
-
W
iring the high-voltage transformers
-
Testing a high-voltage transformer
-
T
esting a magnetron for an open/shorted
filament
For information on accessing and removing parts,
see the A
ppendix.
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 J
apan 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 pr
ocedur
es.
1. Disconnect the oven from the power source.
2.
F
ully discharge the capacitor.
3. Isolate the capacitor from the circuit.
4.
Check for an open or shor
ted capacitor by
placing ohmmeter leads between the capacitor
terminals:
- Escalating ohm readings = capacitor OK
-
Constant infinite resistance = capacitor open
- Constant very low resistance = capacitor
shor
ted
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%. I
f not, replace the capacitor.
Filament Transformers
F
or better operation and reliability, the oven
uses separate transformers in or
der to preheat the
magnetron filament.
The control energizes the filament transformers for
appr
oximately 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.
W
iring the Filament Transformers
The installation of filament transformers is straight-
for
ward. Filament transformers are wired in-phase
and in-line. R
efer to the schematic on page 45,
detailing the pr
oper wiring.
T
o v
erify 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.
NO
TE:
The orange wire always goes to terminal 3
on US models.
T
o verify correct wiring (International), measure
the v
oltage between the taps on FT1 and FT2. The
voltage must be 230 VAC.