Sharp R-4A52 Service Manual page 13

R-4A52
R-4E52
TEST PROCEDURES (CONT'D)
PROCEDURE
LETTER
COMPONENT TEST
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 intinte in one direction and mor than 100 kQ in
the other direction.
CARRY OUT 4R CHECKS
ASYMMETRIC RECTIFIER TEST
CARRY OUT 3D CHECKS.
Isolate the high voltage rectifier assembly from the HV circuit. The asymmetric rectifier can be
tested using an ohmmeter set to its highest range. Connect the ohmmeter 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 directions then the asymmetric rectifier
is good. If an asymmetric rectifier is shorted in either direction, then the the asymmetric rectifier
is probably faultly and must be replaced with the high voltage rectifier. When the asymmetric
rectifier is defective, check whether magnetron, high voltage rectifier, high voltage wire or fila-
ment winding of the power transformer is shorted.
CARRY OUT 4R CHECKS
* +z$":H "OLTAOE RECT,F,ER
C
NOTE:
FOR MEASUREMENT OF THE RESISTANCE OF THE RECTIFIER, THE BATTERIES
OF THE MEASURING INSTRUMENT MUST HAVE A VOLYAGE AT LEAST 6 VOLTS,
BECAUSE O*THERWISE 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.
C.
A normal capacitor shows continuity for a short time (kick) and then a resistance of about
10 Mf2 after it has been charged.
D.
A short-circuited capacitor shows continuity all the time.
E. An open capacitor constantly shows a resistance about 10 MO because of its internal 10
MO resistance.
F.
When the internal wire is opened in the high voltage capacitor, the capacitor shows an in-
finite resistance
G. The resistance across all the terminals and the chassis must be inifinte when the capacitor
is normal.
If incorrect readings are obtained, the high voltage capacitor must be replaced.
CARRY OUT 4R CHECKS
12