Service manual

Page 17

The door on the Evolution oven is monitored by four microswitches. Three of these are used in the

conventional “Primary, Secondary and Monitor” switch arrangement shown below, while the fourth

is a low-voltage switch linked directly to the control circuitry.

Error Light Operation

The “Air Filter Blocked” light and “Service” light are triggered by the internal circuitry. If the magne-

tron overheats, the error code “E:7” or “E:8” is displayed on the front panel, and both the “Air Filter

Blocked” and the “Service” indicators will light. Once the magnetron has cooled sufficiently to allow

the oven to restart, the “Service” light will remain illuminated until the oven is turned off.

This fault may have been triggered by one of the following causes:

- Air inlet on rear of machine being obstructed.

- High air inlet temperature.

- Slow running cooling fan, jammed turntable or broken gearbox

(cooling fan also drives turntable).

- Faulty magnetron overheat ‘stat or associated wiring.

Note that the customer may not have noticed that the oven displayed “E:7” or “E:8” and so

the reported fault may be misleading.

The switches operate as follows:

Primary Interlock [ Top Left-Hand ] and Low voltage [ Top Right-Hand ] Switches

Operate simultaneously. Either will cut off the microwave emissions from the oven when the

door is opened: the Primary switch by breaking the mains supply circuit to the transformers,

and the Low-Voltage switch by breaking the relay circuit on the Power / Relay PCB.

Monitor [ Bottom Outer ] and Secondary Interlock [ Bottom Inner ] Switches.

Operate simultaneously. The Monitor switch will produce a short circuit across the mains

supply if the Primary interlock switch is faulty, thus blowing the microwave fuse and

rendering the oven inoperative. The Secondary interlock switch will cut off the microwave

emission if all three of the other switches have failed.

Note:

If operation of the Monitor switch has caused the Microwave Fuse to blow, the Primary and

Monitor microswitches must be changed, as they may have been damaged by the high

short-circuit currents involved.

Power In

3 Amp

350ºC Stat

Primary

Contactor

coil

Secondary

Crowbar

25 amp

Door Interlock Arrangement

Door Interlock Operation