SHARP R-677(AL)D
Manual de Servicio

TEST PROCEDURES CONT...
PROCEDURE LETTER COMPONENT TEST

JUDGMENT: The measured output power should be at least ± 15 % of the rated output power. CAUTION: 1°C CORRESPONDS TO 80 WATTS. REPEAT MEASUREMENT IF THE POWER IS INSUFFICIENT.

1000g 1000g 1000g

T1�C

T2�C

Heat up for 55 sec B HIGH VOLTAGE TRANSFORMER TEST WARNING: High voltage and large currents are present at the secondary winding and filament winding of the high voltage transformer. It is very dangerous to work near this part when the oven is on. NEVER make any voltage measurements of the high-voltage circuits, including the magnetron filament.

CARRY OUT 3D CHECKS. Disconnect the leads to the primary winding of the high voltage transformer. Disconnect the filament and secondary winding connections from the rest of the HV circuitry. Using an ohmmeter, set on a low range, it is possible to check the continuity of all three winding. The following readings should be obtained:a. Primary winding ................................ approximately 2.5 � b. Secondary winding .......................... approximately 160 � c. Filament winding ......................................... less than 1 � If the readings obtained are not stated as above, then the high voltage transformer is probably faulty and should be replaced. CARRY OUT 4R CHECKS.

C

HIGH VOLTAGE RECTIFIER TEST CARRY OUT 3D CHECKS. Isolate the high voltage rectifier assembly from the HV circuit. The high voltage rectifier can be tested using an ohmmeter set to its highest range. Connect the ohmmeter across the terminal B+C of the high voltage rectifier and note the reading obtained. Reverse the meter leads and note this second reading. The normal resistance is infinite in one direction and more than 100 k� in the other direction. CARRY OUT 4R CHECKS. NOTE: FOR MEASUREMENT OF THE RESISTANCE OF THE RECTIFIER, THE BATTERIES OF THE MEASURING INSTRUMENT MUST HAVE A VOLTAGE AT LEAST 6 VOLTS, BECAUSE OTHERWISE AN INFINITE RESISTANCE MIGHT BE SHOWN IN BOTH DIRECTIONS.

D

HIGH VOLTAGE CAPACITOR TEST CARRY OUT 3D CHECKS. A. Isolate the high voltage capacitor from the circuit. B. Continuity check must be carried out with measuring instrument which is set to the highest resistance range. C. A normal capacitor shows continuity for a short time (kick) and then a resistance of about 10M� after it has been charged. D. A short-circuited capacitor shows continuity all the time. E. An open capacitor constantly shows a resistance about 10 M� because of its internal 10M� resistance. F. When the internal wire is opened in the high voltage capacitor shows an infinite resistance. G. The resistance across all the terminals and the chassis must be infinite when the capacitor is normal. If incorrect reading are obtained, the high voltage capacitor must be replaced. CARRY OUT 4R CHECKS.

R-677 - 15