Sharp R-980J Service Manual page 15

PROCEDURE
LETTER
Initial temperature ............................................................................................. T1 = 11°C
Temperature after (47 + 3) = 50 sec. ................................................................ T2 = 21°C
Temperature difference Cold-Warm (∆T =T2-T1) ............................................ ∆T = 10°C
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 POWER TRANSFORMER TEST
WARNING: High voltages and large currents are present at the secondary winding and
CARRY OUT 3D CHECKS.
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:
If the reading obtained are not stated as above, then the power 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 kΩ in the other direction.
CARRY OUT 4R
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
TEST PROCEDURES
INSUFFICIENT.
1000g
1000g
T1˚C
filament 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. 66 Ω
c. Filament winding ................... less than 1Ω
CHECKS.
COMPONENT TEST
±
Heat up for 50 sec.
A
D2
ASYMMETRIC
RECTIFIER
13
15 % of the rated output power.
1000g
T2˚C
B
D1
HIGH VOLTAGE RECTIFIER
C
R-980J