Sharp R-90GCH Service Manual page 17

PROCEDURE
LETTER
Room temperature ....................... To = 21˚C
Temperature after (42 + 3) = 45 sec. ..................................................................... T2 = 21°C
Temperature difference Cold-Warm .................................................................... ∆T1 = 10°C
Measured output power
The equation is "P = 100 x ∆T" ................................................ P = 100 x 10°C = 1000 Watts
JUDGEMENT: The measured output power should be at least
CAUTION: 1°C CORRESPONDS TO 100 WATTS. REPEAT MEASUREMENT IF THE POWER IS
B HIGH VOLTAGE TRANSFORMER TEST
WARNING: High voltage and large currents are present at the secondary winding and
1. CARRY OUT 3D CHECKS.
2. Remove the back plate from the oven, referring to "BACK PLATE REMOVAL".
3. 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:-
If the readings obtained are not stated as above, then the high voltage transformer is probably
faulty and should be replaced.
4. Also, the high voltage transformer has the thermostat 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 thermostat in the primary coil reaches approximately 160˚C. The thermostat
resets automatically at 105˚C. If an ohmmeter indicates an open circuit under normal condition,
replace the high voltage transformer because the primary coil (thermostat) has opened. An open
primary coil (thermostat) indicates overheating of the high voltage transformer. Check for
restricted air flow to the high voltage transformer, especially the fan motor (high voltage
transformer side).
5. CARRY OUT 4R CHECKS.
C HIGH VOLTAGE RECTIFIER TEST
1. CARRY OUT 3D CHECKS.
2. Remove the back plate from the oven, referring to "BACK PLATE REMOVAL".
3. 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 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.
4. CARRY OUT 4R CHECKS.
TEST PROCEDURES
INSUFFICIENT.
1000g
1000g
T1˚C
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.
a. Primary winding .......................... 1.2 ohms approximately
b. Secondary winding ...................... 95 ohms approximately
c. Filament winding ..................................... less than 1 ohm
COMPONENT TEST
Initial temperature .................... T1 = 11°C
±
Heat up for 45 sec.
15
15 % of the rated output power.
1000g
T2˚C
R-90GCH