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 24V.
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 and red lamps 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
and red lamps of the affected 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 computer will consider
that a fault has occurred and go to
lockout.
34
FAULT FINDING
