Sharp R-350J Service Manual page 11

PROCEDURE
LETTER
JUDGEMENT: The measured output power should be at least
CAUTION: 1°C CORRESPONDS TO 120 WATTS REPEAT MEASUREMENT IF THE POWER IS
B POWER TRANSFORMER TEST
WARNING: High voltages and large currents are present at the secondary winding and filament
1. CARRY OUT 3D CHECKS.
2. Disconnect the leads to the primary winding of the power 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 windings. The following readings should be obtained:
3. If the reading obtained are not stated as above, then the power transformer is probably faulty and should be
replaced.
4. Also, the power transformer has the thermal cut-out in the primary coil. Measure the resistance of the primary
coil. The resistance of the primary coil should be above resistance unless the temperature of the thermal cut-
out in the primary coil reaches approximately 160˚C. The thermal cut-out resets automatically at 140˚C. If
an ohmmeter indicates an open circuit under normal condition, replace the power transformer because the
primary coil (thermostat) has opened. An open primary coil (thermal cut-out ) indicates overheating of the
power transformer. Check for restricted air flow to the power transformer, especially the fan motor or
ventilation openings.
5. CARRY OUT 4R CHECKS.
C HIGH VOLTAGE RECTIFIER ASSEMBLY TEST
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 kΩ 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.
TEST PROCEDURES
INSUFFICIENT.
1000g
1000g
T1˚C
winding of the power 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.
a. Primary winding ........................ approx. 1.2 Ω
b. Secondary winding ................... approx. 102 Ω
c. Filament winding ....................... less than 1Ω
COMPONENT TEST
±
15 % of the rated output power.
Heat up for 38 sec.
B
HIGH VOLTAGE RECTIFIER
9
R-350J
1000g
T2˚C
C