Sharp R-890SLM Service Manual download pdf (Page 16)

R-890SLM

D2 D1

ASYMMETRIC

RECTIFIE

HIGH VOLTAGE

RECTIFIE

A B

[3] C: 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 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 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 recti

ﬁer. When the asymmetric rectiﬁer is defective, check whether magnetron, high voltage rectiﬁer, high voltage wire or ﬁlament winding

of the high voltage 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.

[4] D: HIGH VOLTAGE CAPACITOR TEST

CARRY OUT 3D CHECKS.

1. Isolate the high voltage capacitor from the circuit.

2. Continuity check must be carried out with measuring instrument which is set to the highest resistance range.

3. A normal capacitor shows continuity for a short time (kick) and then a resistance of about 10MΩ after it has been charged.

4. A short-circuited capacitor shows continuity all the time.

5. An open capacitor constantly shows a resistance about 10 MΩ because of its internal 10MΩ resistance.

6. When the internal wire is opened in the high voltage capacitor shows an inﬁnite resistance.

7. The resistance across all the terminals and the chassis must be inﬁnite when the capacitor is normal.

If incorrect reading are obtained, the high voltage capacitor must be replaced.

CARRY OUT

4R CHECKS.

[5] E: SWITCH TEST

CARRY OUT 3D CHECKS.

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

Table: Terminal Connection of Switch

Plunger Operation Common terminal to Normally open terminal Common terminal to Normally close terminal

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.

[6] F: THERMISTOR TEST

CARRY OUT 3D CHECKS.

Disconnect the connector B from CPU unit. Measure the resistance of the thermistor with an ohmmeter. Connect the ohmmeter leads

to Pin No’s C1 and C3 of the thermistor harness.

Room Temperature Resistance

20°C - 30°C Approximately 359.9 kΩ - 152 kΩ

If the meter does not indicate above resistance, replace the thermistor.

CARRY OUT

4R CHECKS.

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Sharp R-890SLM Service Manual Page 16

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