R-90GCK (serv.man7). Test procedure - Sharp Home Appliance Service Manual (repair manual). Page 2

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1.

CARRY OUT 3D CHECKS.

2. Remove the back plate from the oven, referring to “BACK PLATE REMOVAL”.
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 10M

Ω

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.