SHARP R-763(IN)
Service Manual

FUNCTION OF IMPORTANT COMPONENTS
FUSE F1 F8A 250V This fuse blows when monitored latch switch SW1 remains closed with the oven door open and when the contacts (COM + NC) of monitor switch SW2 closes. 1. If the wire harness or electrical components are shortcircuited, this fuse blows to prevent an electric shock or fire hazard. 2. The fuse blows when the asymmetric rectifier, H.V. rectifier, H.V. wire harness, H.V. capacitor, magnetron or secondary winding of power transformer is shorted. SPECIAL FUSE F2 15A If the wire harness or electrical components are shortcircuited, this fuse blows to prevent an electric shock or fire hazard. THERMAL CUT-OUT 125°C TC1 (MG) The thermal cut-out protects the magnetron against overheat. If this temperature goes up higher than 125°C because the fan motor is interrupted, the ventilation openings are blocked, the thermal cut-out TC1 will open and line voltages to the power transformer T will be cut off and the operation of the magnetron MG will be stopped. The defective thermal cut-out TC1 must be replaced with new one. THERMAL CUT-OUT 160°C TC2 (OVEN) The thermal cut-out located on the top the oven cavity is designed to prevent damage to the oven if the foods in the oven catch fire due to over heating produced by improper setting of cook time or failure of control unit. Under normal operation, the oven thermal cut-out remains closed. However, when abnormally high temperatures are reached within the oven cavity, the oven thermal cut-out will open at 160°C, causing the oven to shut down. The defective thermal cut-out TC2 must be replaced with new one. TURNTABLE MOTOR The turntable motor drives the turntable roller assembly to rotate the turntable. FAN MOTOR The fan motor drives a blade which draws external cool air. This cool air is directed through the air vanes surrounding the magnetron and cools the magnetron. This air is channeled through the oven cavity to remove steam and vapours given off from the heating foods. It is then exhausted through the exhausting air vents at the oven cavity. NOISE FILTER The noise filter prevents the radio frequency interference that might flow back in the power circuit. GRILL HEATING ELEMENT GH The grill heating element GH is located on the top of the oven cavity assembly. The grill heating element sends out heat to grill foods. ASYMMETRIC RECTIFIER The asymmetric rectifier is a solid state device that prevents current flow in both directions. And it prevents the temperature rise of the power transformer by blowing the fuse F1 when the high voltage rectifier is shorted.
A
D2 D1

B

ASYMMETRIC RECTIFIER HIGH VOLTAGE RECTIFIER

C

The rated peak reverse voltage of D1 of the asymmetric rectifier is 6 KV. The rated peak reverse voltage of D2 of the asymmetric rectifier is 1.7 KV. D1 and D2 of the asymmetric rectifier or high voltage rectifier are shorted when the each peak reverse voltage goes beyond the each rated peak reverse voltage. (The process of blowing the fuse F1) 1. The high voltage rectifier is shorted by any causes when microwave cooking. 2. The peak reverse voltage of D2 of the rectifier goes beyond the rated peak reverse voltage 1.7 KV in the voltage doubler circuit. 3. D2 of the rectifier is shorted. 4. The large electric currents flow through the high voltage winding of the power transformer. 5. The large electric currents beyond 10A flow through the primary winding of the power transformer. 6. The fuse F1 blows by the large electric currents. 7. The power supply to the power transformer is cut off.

R-763 -

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