Fault Finding
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.
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 in the rear of the oven - the
computer compares the electrical
resistance of this with that set on the
potentiometer and controls the burner
accordingly.
Other inputs to the computer are
signalled by a door switch, 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 are at
24V. The igniter high voltage coils
are mounted on the main PCB.
Upon applying mains voltage, the
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 oven ready light and the red
indicator dial flashing. 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 lamp to
flash green - 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.
27
FAULT FINDING
