Friday, June 17, 2016

LG MICROWAVE OVEN - LCRT2010ST – How to test the microwave output power – How to test the magnetron – how to test the high voltage transformer – How to test the switches – Microwave repair and service

LG  - LCRT2010ST

HOW TO MEASURE THE MICROWAVE OUTPUT POWER
Microwave power output measurement is made with the microwave oven supplied at its rated voltage and operated at its maximum microwave power setting with a load of (1000±5) g of potable water.
# The water is contained in a cylindrical borosilicate glass vessel having a maximum material thickness of 3 mm and an outside diameter of approximately 190mm.
# The oven and the empty vessel are at ambient temperature prior to the start of the test.
# The initial temperature (T1) of the water is (10±2)°C. It is measured immediately before the water is added to the vessel. After addition of the water to the vessel, the load is immediately placed on the center of the turntable which is in thd lowest position and the microwave power switched on.
# The time T for the temperature of the water to rise by a value DeltaT of (10±2)°K is measured, where T is the time in seconds and Delta T is the temperature rise. The initial and final water temperatures are selected so that the maximum difference between the final water temperature and the ambient temperature is 5°K.
# The microwave power output P in watts is calculated from the following formula :
P = 4187 x (DeltaT) + 0.55 X (T2 - T0 ) X M/T
T2: Temperature after heating
T0: Temperature of bowl
M: Weight of bowl is measured while the microwave generator is operating at full power. Magnetron filament heat-up time is not included. (about 3 sec)
# The water is stirred to equalize temperature throughout the vessel, prior to measuring the final water temperature.
# Stirring devices and measuring instruments are selected in order to minimize addition or removal of heat.
TEST PROCEDURE
HIGH VOLTAGE TRANSFORMER TEST
1. Measure the resistance.
(Ohm-meter scale: Rx1 and Rx100)
# Primary winding
# Secondary winding
# Filament winding
Approx.: 0.2 ~ 0.4 ohm
Approx.: 70 ~ 100 ohm
Less than: 1 ohm
2. Measure the resistance.
(Ohm-meter scale: Rx1000)
# Primary winding to ground
# Filament winding to ground
Normal: Infinite
Normal: Infinite
MAGNETRON TEST
1. Measure the resistance.
(Ohm-meter scale: Rx1)
# Filament terminal
Normal: Less than 1 ohm
2. Measure the resistance.
(Ohm-meter scale: Rx1000)
# Filament to chassis
Normal: Infinite
PRIMARY INTERLOCK SWITCH TEST
When the door release button is depressed slowly with the door closed, an audible click should be heard at the same time or successively at intervals. When the button is released slowly, the latches should activate the switches with an audible click.
If the latches do not activate the switches when the door is closed, the switches should be a adjusted in accordance with the adjustment procedure. Disconnect the wire lead from the primary switch. Connect the ohmmeter leads to the common (COM) and normally open (NO) terminal of the switch. The meter should indicate an open circuit in the door open condition. When the door is closed, the meter should indicate a closed circuit. When the primary switch operation is abnormal, make the necessary adjustment or replace the switch only with the same type of switch.
B. SECONDARY INTERLOCK SWITCH TEST
Disconnect the wire lead from the secondary switch. Connect the ohmmeter leads to the common (COM) and normally open (NO) terminals of the switch. The meter should indicate a open circuit in the door open condition. When the door is closed, meter should indicate an closed circuit. When the secondary switch operation is abnormal, make the necessary adjustment or replace the switch only with the same type of switch.
C. MONITOR SWITCH TEST
Disconnect the wire lead from the monitor switch. Connect the ohmmeter leads to the common (COM) and normally closed (NC) terminals of the switch. The meter should indicate closed circuit in the door open condition. When the door is closed, meter should indicate an open circuit. When the monitor switch operation is abnormal, replace with the same type of switch.
NOTE: After repairing the door or the interlock system, it is necessary to do this continuity test before operating the oven.