R-8000GK - Sharp Home Appliance Service Manual (repair manual). Page 12

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3. 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 winding. The following readings should be obtained:-

a. Primary winding .................................... 1.3 ohms approximately
b. Secondary winding ................................. 95 ohms approximately
c. Filament winding ...............................................  less than 1 ohm

If the readings obtained are not stated as above, then the high voltage transformer is probably faulty and
should be replaced.

4. Also, the high voltage transformer has the thermostat in the primary coil. Measure the resistance of the

primary coil. The resistance of the primary coil should be above resistance unless the temperature of the
thermostat in the primary coil reaches approximately 160˚C. The thermostat resets automatically at 105˚C.
If an ohmmeter indicates an open circuit under normal condition, replace the high voltage transformer
because the primary coil (thermostat) has opened. An open primary coil (thermostat) indicates overheating
of the high voltage transformer. Check for restricted air flow to the high voltage transformer, especially the
fan motor (high voltage transformer side).

5. CARRY OUT 4R CHECKS.

1. CARRY OUT 3D CHECKS.
2. Remove the back plate from the oven, referring to “BACK PLATE REMOVAL”.
3. 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 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.

4. 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.

1. CARRY OUT 3D CHECKS.
2. Remove the back plate from the oven, referring to “BACK PLATE REMOVAL”.
3. Isolate the high voltage capacitor from the circuit.
4. Continuity check must be carried out with measuring instrument which is set to the highest resistance range.
5. A normal capacitor shows continuity for a short time (kick) and then a resistance of about 10M

Ω after it has

been charged.

6. A short-circuited capacitor shows continuity all the time.
7. An open capacitor constantly shows a resistance about 10 M

Ω because of its internal 10MΩ resistance.

8. When the internal wire is opened in the high voltage capacitor, the capacitor shows an infinite resistance.
9. 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.

10. CARRY OUT 4R CHECKS.

1. CARRY OUT 3D CHECKS.
2. Isolate the switch to be tested and using an ohmmeter check between the terminals as described in the

following table.

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

3. CARRY OUT 4R CHECKS.

Table: Terminal Connection of Switch

Plunger Operation

COM to NO

COM to NC

Released

Open circuit

Short circuit

Depressed

Short circuit

Open circuit

COM; Common terminal,
NO;

Normally open terminal

NC;

Normally close terminal

1. CARRY OUT 3D CHECKS.
2. Remove the back plate from the oven, referring to “BACK PLATE REMOVAL”.