R-8740 (serv.man17). Complete - Sharp Home Appliance Service Manual (repair manual). Page 14

R-8740M  - 14

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.

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 IEC-60705 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 2 minutes on full power.
4. When the 2 minutes is completed, remove the  container and stir the water. Note temperature as T2.
5. Calculate the output power using the following formula:

R.F. Power Output = (T2 - T1) x 80.

±

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 Technical Training notes (part number SERV-LITMW01). The maximum
leakage permitted in BS EN 60335-2-25 is 50W/m

2 

(equivalent to 5W/m

2

), however 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
APOLLO X1

NEVER TOUCH ANY PART IN THE CIRCUIT WITH YOUR HAND OR AN INSULATED TOOL WHILE
THE OVEN IS IN OPERATION.