Sharp R-880B Service Manual page 15

PROCEDURE
LETTER
Initial temperature .................................................................................................. T1 = 11 C
Temperature after (47 + 2) = 49 sec ...................................................................... T2 = 21 C
Temperature difference Cold-Warm ....................................................................... T1 = 10C
Measured output power
The equation is "P = 90 x T" ...................................................... P = 90 x 10 C = 900 Watts
JUDGMENT: The measured output power should be at least
CAUTION: 1 C CORRESPONDS TO 90 WATTS. REPEAT MEASUREMENT IF THE POWER IS
B HIGH VOLTAGE TRANSFORMER TEST
WARNING:
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 windings. 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.
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 k
CARRY OUT 4R CHECKS.
ASYMMETRIC RECTIFIER TEST
CARRY OUT 3D CHECKS.
Isolate the high voltage rectifier assembly from the HV circuit. The asymmetric can be tested using an
ohmmeter set to its highest range across the terminals A+B of the asymmetric rectifier and note the
reading obtained. Reverse the meter leads and note this second reading. If an open circuit is indicated
in both direction then the asymmetric rectifier is good. If an asymmetric rectifier is shorted in either
direction, then the asymmetric rectifier is probably faulty and must be replaced with high voltage
rectifier. When the asymmetric rectifier is defective, check whether magnetron, high voltage rectifier,
high voltage wire or filament winding of the high voltage transformer is shorted.
CARRY OUT 4R CHECKS.
TEST PROCEDURES
INSUFFICIENT.
1000g
1000g
T1˚C
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.
a. Primary winding ................................ approximately 1.7
b. Secondary winding .......................... approximately 118
c. Filament winding......................................... less than 1
COMPONENT TEST
15 % of the rated output power.
Heat up for 49 sec
A
D2 D1
ASYMMETRIC
RECTIFIER
C
13
1000g
T2˚C
in the other direction.
B
HIGH VOLTAGE RECTIFIER
R-880B