Sanyo EM-U1000W - Compact Microwave,10 Pwr Lvls,800 W,18"x14-3/8"x11-5/8",WE Service Manual

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Sanyo EM-U1000W - Compact Microwave,10 Pwr Lvls,800 W,18"x14-3/8"x11-5/8",WE Service Manual Manual pdf 6 page image

4anode currentIb(mA)anode voltageeb (kV)mFig.2-411..22 MMIICCRROOWWAAVVEE GGEENNEERRAATTEERRMicrowave generator is the heart of microwave oven. The quality of a microwave oven mostly depends on thequality of the microwave generator. A microwave generator is mainly composed of magnetron and its powersupply circuit, FIG.2-3 is the typical circuit diagram of the present used microwave oven’s generator. The powersupply circuit is composed of rectifying circuit and filament circuit.Usually, we adopt continuous wave magnetron. It can turn the direct energy, which is applied to the magnetronafter being high voltage rectified to microwave energy, the power supply circuit supply a direct high voltagebetween the cathode and anode of the magnetron, a filament voltage to the cathode filament of the magnetron.The working process of the magnetron: When the anode voltage gradually rises from zero, the anode current isapprox. zero, the power is very small as well. When the anode voltage rises to “THRESHOLD” voltage value, themagnetron starts oscillating, and the anode current would increase obviously, provided the anode voltage rises alittle more, the anode current would increase a lot (FIG.2-4), and would reach the rate value quickly.If the anode voltage is undulating, it would cause the anodecurrent swing fiercely, even made the magnetron stop oscillating.For keeping a steady output, the power supply circuit of theoven must supply a stead direct current voltage. The filamentvoltage of the magnetron must be supplied by an alternatingcurrent voltage. For simplifying the circuit, it would be suppliedby the same leakage magnetic transformer with the anodepower (high voltage power). The filament of the magnetron hasbeen treated with special techniques and has the ability to be"cold booted". But when started in cold, there still is a verystrong surge electric field attached to the surface of the anode,and would be harmful to the anode. In order to reduce the surgevoltage, the filament of the magnetron must be connected as theFIG.2-3 shown. In this figure, when the anode current of themagnetron circulates, the filament current should flow to the FAend from the lower end.11..33 CCOOOOLLIINNGG SSYYSSTTEEMMIn the working process of the microwave oven, the magnetron often makes the anode temperature rise due toanode loss caused by the electronics strike the oven surface and the heat radiate of the cathode. To prevent theanode temperature rise too high, thus affect the working steady and its life span, it is necessary to cool themagnetron. According to the different models and rate output of the magnetron, compelling wind cooling andflowing water-cooling can be adopted. Usually, the home used microwave oven adopts the compelling windcooling method, and all are fixed with cooling fin.Cooling system includes fan motor, air duct, air entrance, air vent etc. The flowing direction of the cooling windshould. Be parallel to the cooling fin of the magnetron. Generally, we adopt the method of air blast rather than airabsorb. And all the cabinet of the oven is with air entrance and air vent, the hot wind blowing through themagnetron is guided with air tube to improve the cooling effect. In the technical parameter chart of the magnetron,it usually will give out the requirement of cooling wind. A shortage of cooling wind would damage the character ofthe magnetron, even burn out the magnetron. The amount that the fan blasted should not be less than therequirement. When fix the fan, attention must be paid to prevent the cool wind from blowing directly to the glasspart of the magnetron to avoid blasting.11..44 EELLEECCTTRRIICC CCOONNTTRROOLL SSYYSSTTEEMMIn mechanical control microwave ovens, electric control systems is mainly composed of interlock switch, timer,power distributor, and thermal cutout, etc. The electric control system of those tough control microwave oven ismainly composed of interlock switch, computer controller and thermal cutout, etc.