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TurboChef Technologies, Inc. C Series
9-7
Filament Transformer(102091)
Background:
The filament transformer is a step down
transformer from 208-240VAC to about 4-5VAC.
This voltage pre-heats the magnetron filament
allowing it to be ready once the magnetron is
energized by the high voltage transformer. This
method in the industry is known as hot start and
highly used to increase the life expectancy of the
magnetron.
The filament transformer and stirrer motor are
energized by K3 relay when the control signal is
grounded at the same time, K1 relay is energized
to provide power to the magnetron cooling fan.
Both relays, by means of software, will remain in
the ON state for 3 minutes after the
MAGNETRON circuit has been turned OFF. The
typical failure mode of the filament transformer is
intermittent operation, meaning that it may not
delivered 4-5 volts to the filament of the
magnetron, thus not pre-heating the magnetron
filament. In this cases the current going to the
high voltage transformer may lag. This can result
in a "MAG CURR LOW" message.
DANGER!!: Do not attempt to measure
voltage at pins 4 and 5 of filament transformer
without actually isolating it from the high voltage
circuit (disconnect anode transformer, capacitor,
magnetron and diode). If not isolated the circuit
will have a potential of 4800 volts.
Checking the filament transformer
DANGER!! HIGH VOLTAGE
Step 1: Disconnect anode wire from T1
transformer (pin 7 or 6 on transformer) and place
circuit breaker in the OFF position; this will isolate
the high voltage part of the microwave circuit.
Next, disconnect the wires going to the
magnetron and connect them to your voltmeter
(select AC mode).
Step 2: Place oven in TEST mode. Press BACK
key until the oven screen displays " OVEN OFF"
then Press and hold the BACK and ENTER keys
simultaneously and then key in PIN # 9-4-2-8
(access code) then ENTER. This will allow you to
enter into the test mode to manually energize the
magnetron.
Step 3: Press and release immediately the
MGTRON key and observe the voltage at
voltmeter, reading should be around 4.6VAC.