Read Sharp R-1900M (serv.man7) Service Manual online
R1900M
6 – 3
[3] C: HIGH VOLTAGE RECTIFIER (1) AND/OR (2) TEST
1. HIGH VOLTAGE RECTIFIERFTEST
1. CARRY OUT 3D CHECKS.
2. 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 100k ohms in the other direction.
second reading. The normal resistance is infinite in one direction and more than 100k ohms in the other direction.
3. CARRY OUT 4R CHECKS.
2. ASYMMETRIC RECTIFIER TEST
1. CARRY OUT 3D CHECKS.
2. Isolate the high voltage rectifier assembly from the HV circuit. The asymmetric rectifier 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 directions then the asymmetric rectifier is good. If the asymmetric rectifier is shorted in either direction, then the
asymmetric rectifier is faulty and must be replaced with high voltage rectifier. When the asymmetric rectifier is defective, check whether magne-
tron, high voltage rectifier, high voltage wire or filament winding of the power transformer is shorted.
open circuit is indicated in both directions then the asymmetric rectifier is good. If the asymmetric rectifier is shorted in either direction, then the
asymmetric rectifier is faulty and must be replaced with high voltage rectifier. When the asymmetric rectifier is defective, check whether magne-
tron, high voltage rectifier, high voltage wire or filament winding of the power transformer is shorted.
3. CARRY OUT 4R CHECKS.
NOTE: Be sure to use an ohmmeter that will supply a forward bias voltage of more than 6.3 volts.
[4] D: HIGH VOLTAGE CAPACITOR (1) AND/OR (2) TEST
1. CARRY OUT 3D CHECKS.
2. If the capacitor is open, no high voltage will be available to the magnetron. Disconnect input leads and check for short or open between the termi-
nals using an ohmmeter.
Checking with a high ohm scale, if the high voltage capacitor is normal, the meter will indicate continuity for a short time and should indicate an
open circuit once the capacitor is charged. If the above is not the case, check the capacitor with an ohmmeter to see if it is shorted between either
of the terminals and case. If it is shorted, replace the capacitor.
open circuit once the capacitor is charged. If the above is not the case, check the capacitor with an ohmmeter to see if it is shorted between either
of the terminals and case. If it is shorted, replace the capacitor.
3. CARRY OUT 4R CHECKS.
[5] E: SECONDARY INTERLOCK SWITCH (1) AND/OR (2) TEST
1. CARRY OUT 3D CHECKS.
2. Isolate the switch and connect the ohmmeter to the common (COM.) and normally open (NO) terminal of the switch. The meter should indicate an
open circuit with the door open and a closed circuit with the door closed. If improper operation is indicated, replace the secondary interlock switch.
3. CARRY OUT 4R CHECKS.
[6] F: PRIMARY INTERLOCK SYSTEM TEST
1. DOOR SENSING SWITCH
1. CARRY OUT 3D CHECKS.
2. Isolate the switch and connect the ohmmeter to the common (COM.) and normally open (NO) terminal of the switch. The meter should indicate an
open circuit with the door open and a closed circuit with the door closed. If improper operation is indicated, replace the door sensing switch.
3. CARRY OUT 4R CHECKS.
2. PRIMARY INTERLOCK RELAY RY1
1. CARRY OUT 3D CHECKS.
2. Disconnect two (2) wire leads from the male tab terminals of the Primary Interlock Relay RY1. Check the state of the relay contacts using a ohm-
meter. The relay contacts should be open. If the relay contacts are closed, replace the circuit board entirely or the relay itself.
3. CARRY OUT 4R CHECKS.
[7] G: MONITOR SWITCH (1) AND/OR (2) TEST
1. CARRY OUT 3D CHECKS.
D2
D1
ASYMMETRIC
RECTIFIER
HIGH VOLTAGE
RECTIFIER
A
B
C
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