Sharp R-7A55, Service Manual

Page: 15 / 48

13
R-7A55(W)/(B)
R-7E45(W)/(B)
PROCEDURE
LETTER
COMPONENT TEST
6. Measure the final water temperature. (Example: The final temperature T2 = 21
°
C)
7. Calculate the microwave power output P in watts from above formula.
Initial temperature ......................................................................................................... T1 = 11
°
C
Temperature after (42 + 2) = 44 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
TEST PROCEDURES (CONT'D)
JUDGMENT: The measured output power should be at least
±
15 % of the rated output power.
CAUTION: 1
°
C CORRESPONDS TO 100 WATTS. REPEAT MEASUREMENT IF THE POWER IS
INSUFFICIENT.
A B
C
D2 D1
ASYMMETRIC
RECTIFIER
HIGH VOLTAGE RECTIFIER
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
Ω
in the other direction.
CARRY OUT 4R CHECKS
ASYMMETRIC RECTIFIER TEST
CARRY OUT 3D CHECKS.
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 reading obtained are not stated above, then the high voltage transformer is probably faulty and
should be replaced.
CARRY OUT 4R CHECKS
a. Primary winding 1.22 ohms approximately
b. Secondary winding 81.7 ohms approximately
c. Filament winding less than 1 ohm
WARNING: High voltages and large currents are present at the secondary winding and
filament winding 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.
B HIGH VOLTAGE TRANSFORMER TEST
1000g
1000g
1000g
T1˚C
T2˚C
Heat up for 44 sec.