Pratica Copa Express, Service Manual

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56
MICROWAVE SYSTEM
The Microwave System
The Microwave is the most complex system in the oven. Extreme caution must be taken during
servicing to protect both the operator and technician.
The Microwave portion of the unit consist of several components that make up a left and right system.
For safety precautions, both left and right microwave systems utilize a 20A fuse that will blow if an
over-current situation occurs shutting off the microwave system immediately preventing further
component damage.
How It Works
When the transformer is supplied with power, a voltage of 3.6V and 2000V are generated in the
secondary. The 3.6V voltage, as we have seen, heats the filament of the Magnetron that emits
electrons. The 2000V volts supply the positive half cycle of the alternate current voltage and charges
the capacitor. In this half cycle, the diode works as a short circuit allowing the entire current pass
through it.
In the negative half cycle, the voltage of the capacitor and the 2000 volts are added resulting in a
4000V system. In this half cycle, the diode works as bridge allowing the current to flow to the
Magnetron that generates the microwaves.
Then the supply of the circuit is turned off, all the voltage stored in the capacitor is discharged by the
drainage resistor.
Microwave Protection System
The microwave protection system is responsible for protecting the circuit components and assuring
the oven functions correctly. The system will prevent the microwave circuit from operating while the
door is open.
The Microwave Circuit Protection System is formed by two 20A fuses (one for each circuit), two
302°F/150° thermostats, two relays and three micro switches.