Pratica Chef Express, Service Manual

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56
MICROWAVE SYSTEM
Microwave Relay
The microwave relay is responsible for energizing the magnetrons by sending power to the high
voltage transformers. The control board is monitoring the position of the door through the primary
and secondary door switches (SW1 & SW2). If either one of these switches open the board will de-
energize this relay.
Interlock Relay
The interlock relay works in series with the monitor door switch (SW3). This switch is an integral part
of the interlock safety system. The control board sends constant 12V DC power to this relay to open
the normally closed contacts. These contacts are connected to L1 and L2 power. If the magnetron
relay is energized and this monitor switch opens, a dead short will occur blowing the 20-amp fuses
and disabling the oven for safety. This is the third method to prevent microwave energy from leaving
the cavity during an open-door condition.
Voltage Relay
The voltage relay is responsible for applying the correct voltage to the microwave high voltage
transformers. The control board determines the voltage based on the current transformer and then
sends the control voltage to the relay to switch between 208V and 240V accordingly.
Relay Test
1) Unplug the oven and disconnect the white 12V DC coil voltage wires.
2) Measure the continuity between the terminals of the relay coil.
•
If the multimeter measures continuity, the relay is good.
•
Is no continuity is present, replace the relay.
3) If continuity is present on the coil terminals, plug wires back in and
test for 12V DC across the coil terminals.
•
If DC voltage is present, the main control board is good and relay must be replaced.
•
If DC voltage is not present, check continuity on coil voltage wires going back to the board
and if continuity is present, replace the control board.