R-4G75M (serv.man3). Section 2 Test procedures, LSI table (page 8-22) - Sharp Home Appliance Service Manual (repair manual). Page 4

11

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 asymmetric rectifier is probably faulty 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 filament winding of the power transformer is shorted.

CARRY OUT 4R CHECKS

NOTE: FOR MEASUREMENT OF THE RESISTANCE OF THE RECTIFIER, THE BATTERIES OF THE

MEASURING INSTRUMENT MUST HAVE A VOLTAGE AT LEAST 6 VOLTS, BECAUSE
OTHERWISE AN INFINITE RESISTANCE MIGHT BE SHOWN IN BOTH DIRECTIONS.

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 M

Ω

 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 M

Ω

 because of its internal 10 M

Ω

 resistance.

F. When the internal wire is opened in the high voltage capacitor, the capacitor shows an infinite

resistance.

G. The resistance across all the terminals and the chassis must be infinite when the capacitor is  normal.
If incorrect readings are obtained, the high voltage capacitor must be replaced.

CARRY OUT 4R CHECKS

CARRY OUT 3D CHECKS

Isolate the switch to be tested and using an ohmmeter check between the terminals as described in the
following table.

COM;

Common terminal

NO;

Normally open terminal

NC;

Normally close terminal

Table: Terminal Connection of Switch

Plunger Operation

COM to NO

COM to NC

Released

Open circuit

Short circuit

Depressed

Short circuit

Open Circuit

If incorrect readings are obtained, make the necessary switch adjustment or replace the switch.

CARRY OUT 4R CHECKS.

CARRY OUT 3D CHECKS

Disconnect the leads from the terminals of the thermal cut-out. Then using an ohmmeter, make a continuity
test across the two terminals as described in the below.

CARRY OUT 4R CHECKS

Table: Thermal Cut-out Test

PARTS NAME

THERMAL CUT-OUT

THERMAL CUT-OUT

THERMAL CUT-OUT

   Condition

125

°

C (MAG)

150

°

C (GRILL)

160

°

C (OVEN)

Temperature of ”ON” condition

This is not resetable type

130

°

C

This is not resetable type

(closed circuit)

Temperature of ”OFF” condition

Above 125

°

C

Above 150

°

C

Above 160

°

C

(open circuit)

Indication of ohmmeter (When room

Closed circuit

Closed circuit

Closed circuit

temperature is approx. 20

°

C.)

If incorrect readings are obtained replace the thermal cut-out.