8 – 1
 A: MAGNETRON TEST
CARRY OUT 3D CHECKS.
Isolate the magnetron from high voltage circuit by removing all leads connected to filament terminal.
To test for an open circuit filament use an ohmmeter to make a continuity test between the magnetron filament terminals, the meter should show a
reading of less than 1 ohm.
To test for short filament to anode condition, connect ohmmeter between one of the filament terminals and the case of the magnetron (ground). This
test should be indicated an infinite resistance. If a low or zero resistance reading is obtained then the magnetron should be replaced.
1. MICROWAVE OUTPUT POWER
The power output of this oven is rated using the method specified by IEC 60705. Full details of how to curry out this procedure can be found in the
Sharp Technical Training notes which is available from Sharp Parts Centre (part number SERV-LITMW01).
The IEC60705 procedure must be carried out using laboratory-type procedures and equipment.
These requirements make the procedure unsuitable for routine performance checks.
NOTE: The following test method gives an indication of the output power only, it cannot be used to establish the actual/rated output
power. If the true output power is required, then the IEC60705 test method must be used.
Alternative simplified method:
1. Place 2 litres of cold water (between 12
°C and 20°C) in a suitable container.
2. Stir the water and measure the temperature in
°C. Note temperature as T1.
3. Place the container in the microwave and heat the water for 1 minute and 36 seconds on full power.
NOTE: The operation time of the microwave oven includes “3” sec. (3 sec. is magnetron filament heat-up time.)
4. When the 1 minute and 36 seconds is completed, remove the container and stir the water. Note the water temperature as T2.
5. Calculate the output power using the following formula:
R.F. Power Output = (T2 - T1) x 90.
NOTE: The result from this test should be within the allowance of 2000cc alternative method. (
2. MICROWAVE LEAKAGE TEST
This oven should be tested for microwave leakage on completion of any repair or adjustment, following the procedure described in the Sharp Techni-
cal Training notes (part number SERV-LITMW01). The maximum leakage permitted in BS EN 60335-2-25 is 50W/m
(equivalent to 5W/m
it is not normal to detect any significant leakage, therefore, any leakage which is detected should be investigated.
It is essential that only leakage detectors with current calibration traceable to National Physical Laboratories are used.
Suitable leakage detectors: CELTEC A100
 B: HIGH VOLTAGE TRANSFORMER TEST
1. CARRY OUT 3D CHECKS.
2. 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 -------------------- approximately 1.98
b.Secondary winding --------------- approximately 159.5
c.Filament winding --------------------------- less than 1
If the readings obtained are not stated as above, then the high voltage transformer is probably faulty and should be replaced.
3. CARRY OUT 4R CHECKS.
NEVER TOUCH ANY PART IN THE CIRCUIT WITH YOUR HAND OR AN INSULATED TOOL WHILE THE OVEN IS IN OPERATION.
WARNING: High voltages and large currents are present at the secondary winding and filament winding of the power transformer. It is
very dangerous to work near this part when the oven is on. NEVER make any voltage measurements of the high-voltage cir-
cuits, including the magnetron filament.