Method of operation
When the control knob is rotated from
the ‘OFF’ position, a microswitch
closes and allows the gas control
solenoids to be energised; the same
movement of the control rotates an
electrical potentiometer and lights a
red LED.
The micro-computer on the main
control board uses the resistance set
at the potentiometer to determine the
user’s requirements - ie; oven or grill
and oven temperature asked for.
The oven temperature is sensed by a
thermistor at the rear of the oven - the
computer compares the electrical
resistance of this with that set on the
potentiometer, and controls burner
accordingly.
Other inputs to the micro-computer are
signalled by door switches, the timer /
programmer unit and an air flow
checking pressure switch.
The oven fan, cooling fan, and lamps
are operated at mains voltage, the
solenoid valves, and controls at 25V.
The igniter high voltage coils are
mounted on the main PCB.
Upon applying mains voltage, the
micro-computer makes a series of checks
of the air flow and flame detector
before allowing start up.
Electrical faults
These may be either component failure
or wiring / connector faults. Should
any disconnections be made, it is
important that they be re-connected
exactly as before or the computer will
lock out; poor connections are the most
common fault. It is most important that
earth wires (green) are all connected
and earth screws tight.
There are two forms of micro-
computer lockout
Hard lockout (
HLO
); for instance, air
flow failure. This is indicated by the
green lamps and red indicator dials of
both ovens flashing alternately left /
right. The cooling fan may continue to
run for a while. Hard lockout can only
be cancelled by turning off the mains
electricity supply.
Soft lockout (
SLO
), for instance, re-
ignition failure, will cause the green
lamp and red indicator dial of the
main oven cavity to flash - the cooling
fan may run on, the oven fan will not
run on. To cancel soft lockout, turn off
the control knob.
Should the oven temperature not
reach 40˚C within approximately
four minutes, the micro-computer will
consider that a fault has occurred and
go to lockout.
25
FAULT FINDING
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