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13

1. Unplug lead connectors to power relay B and verify

continuity of power relay B 1-2 terminals.

2. Unplug lead connectors to primary latch switch and

secondary latch switch.

3. Test the continuity of switches at door opened and closed

positions with ohmmeter (low scale).

Normal continuity readings should be as follows.

1. Unplug lead wires from H.V.transformer primary terminals.
2. Connect test probes of ohmmeter to the disconnected leads

which were connected to the H.V.transformer.

3. Test the continuity of short switch with door opened and

closed positions with ohmmeter (low scale).

Normal continuity readings should be as follows.

1. Remove connections from the transformer terminals and

check continuity.

2. Normal continuity readings should be as follows.

Secondary winding ........ Approx. 80

Ω

 - 120

Ω

Filament winding............ Approx. 0

Ω

Primary winding ............. Approx. 0

Ω

 - 3

Ω

1. Check continuity of capacitor with meter on highest OHM

scale.

2. A normal capacitor will show continuity for a short time, and

then indicate 9M

Ω

 once the capacitor is charged.

3. A shorted capacitor will show continuous continuity.

4. An open capacitor will show constant 9M

Ω

.

5. Resistance between each terminal and chassis should be

infinite.

Continuity checks can only indicate an open filament or a
shorted magnetron. To diagnose for an open filament or shorted
magnetron.
1. Isolate magnetron from the circuit by disconnecting the

leads.

2. A continuity check across magnetron filament terminals

should indicate one ohm or less.

3. A continuity check between each filament terminal and

magnetron case should read open.

CAUTION 

1. High voltage is present at the high voltage terminal of the

high voltage transformer during any cook cycle.

2. It is neither necessary nor advisable to attempt

measurement of the high voltage.

3. Before touching any oven components, or wiring, always

unplug the oven from its power source and discharge the
high voltage capacitor.

DOOR 

OPENED

DOOR 

CLOSED

PRIMARY LATCH SWITCH

∞Ω 

(open)

0

Ω 

(closed)

SECONDARY LATCH SWITCH

∞Ω 

(open)

0

Ω 

(closed)

POWER RELAY B

∞Ω 

(open)

∞Ω 

(open)

DOOR 

OPENED

DOOR 

CLOSED

MECHANICAL MODELS

Some ohm

(see NOTE)

0

Ω

SECONDARY
WINDING
TERMINALS

PRIMARY
WINDING
TERMINALS

0

Ω

RX1

0

Ω

-3

Ω

SCALE

RX1
SCALE

80

Ω

-120

Ω

FILAMENT
WINDING
TERMINALS

HIGHEST

HIGH

HIGHEST

OHM
SCALE

OHM
SCALE

VOLTAGE
CAPACITOR

ANTENNA

COOLING

MAGNETRON

ANTENNA GASKET

FILAMENT
TERMINALS

HIGHEST
OHM
SCALE

CASE

FIN

RX1
SCALE

14

1. Isolate the diode from the circuit by disconnecting the leads.
2. With the ohmmeter set the highest resistance scale,

measure the resistance across the diode terminals. Reverse
the meter leads and again observe the resistance reading.
Meter with 6V, 9V or higher voltage batteries should be used
to check the front to back resistance of the diode, otherwise
an infinite resistance may be read in both directions. A
normal diode’s resistance will be infinite in one direction and
several hundred K

Ω

 in the other direction.

1. Isolate the protector diode assembly from the circuit by

disconnecting its leads.

2. With the ohmmeter set at the highest resistance scale,

measure the resistance across the protector diode terminals.
Reverse the meter leads and again observe the resistance
reading. A normal protector diode’s resistance will be infinite
in both directions.
It is faulty if it shows continuity in one or both directions.

1. Isolate the variable power switch from the circuit by

disconnecting 2 leads.

2. In order to check if variable power controller is operating

normally, follow the test procedure below.
(a)

Select any power other than “High” and start the oven.

(b)

Check continually between both terminals of the
variable power switch.

(c)

Variable power controller (timer and variable power
switch) is working properly if the ohmmeter reads open
and 0 ohm within 26.4 ± 2 seconds interval.

FORWARD

NOTE: OHMMETER SHOULD HAVE A MINIMUM

8 VOLT BATTERY

SEVERAL

HUNDRED K

REVERSE

HIGHEST
OHM
SCALE

TIMER

VARIABLE
POWER 
SWITCH

15

1. When mounting primary latch switch, secondary latch switch

and short switch to door hook assembly, mount the primary
latch switch, the secondary latch switch and the short switch
to the door hook assembly as shown in the illustration.

2. When mounting the door hook assembly to the oven

assembly, adjust the door hook assembly by moving it in the
direction of arrow (in the illustration) so that the oven door
will not have any play in it. Check for play in the door by
pulling the door assembly. Make sure that the latch keys
move smoothly after adjustment is completed. Completely
tighten the screws holding the door hook assembly to the
oven assembly.

The output power of the magnetron can be determined by
performing IEC standard test procedures. However, due to the
complexity of IEC test procedures, it is recommended to test the
magnetron using the simple method outlined below.
Necessary equipment:
•

1 litre beaker

•

Glass thermometer

•

Wrist watch or stopwatch.

Output power performance test procedure
1. Fill the beaker with exactly one litre of tap water. Stir the

water using the thermometer and note the temperature
(record as T1).

2. Place the beaker on the centre of glass cook plate.
3. Set to high power and heat for exactly one minute.
4. Stir the water again with the thermometer and note the

temperature (record as T2).

5. The normal temperature rise (T1-T2), should be more than

7.0°C using the high power selection with the oven operating
at specified line voltage.

Please confirm that the gap between the switch housing and switch
actuator levers is no more than 1.0mm when the door is closed.

DOOR

SCREW

PRIMARY

DOOR HOOK 

SHORT 

SECONDARY

SCREW

LATCH
SWITCH

ASSY

SWITCH

LATCH
SWITCH

SWITCH

GAP SHOULD 

ACTUATOR
LEVEL

BE < 1 MM

16

First of all operate the oven by following the operating procedures exactly in order to find the symptom.

1. Check the unit is grounded before commencing any troubleshooting.
2. Do not take measurements in the high voltage circuit.
3. Discharge the high voltage capacitor.
4. When checking the continuity of the switches or the high voltage transformer, disconnect one lead wire from these parts and

then check continuity with the AC plug removed. To do otherwise may result in a false reading or damage to your meter.

5. Do not touch any parts of the circuitry on the digital programmer circuit, since static electric discharge may damage this control

panel. Always connect yourself to ground to discharge any static from your body.

SYMPTOMS

CAUSE

CORRECTIONS

1.

Oven is dead.
Fuse is OK.

1.

Open or loose lead wire harness.

2.

Open thermal cutout.

3.

Defective timer switch.

Check fan motor when thermal cutout is
defective.

2.

Oven lamp operates normally but fan motor
does not rotate.

1.

Misalignment or loose wiring of primary
latch switch.

Adjust door and latch switches.

2.

Defective primary latch switch.

4.

Oven lamp and fan motor operate normally but
no microwave oscillation.

1.

Off-alignment of latch switches.

Adjust door and latch switches.

2.

Defective secondary latch switch.

3.

Defective or loose wiring of variable power
switch.

4.

Defective variable power switch or timer
switch.

Refer to component test procedure.

5.

Open or loose connection of high voltage
circuit especially magnetron filament circuit.

NOTE: Large contact resistance will bring lower

magnetron filament voltage and cause
magnetron to have lower output and/or
be intermittent.

6.

Defective high voltage component:

 

H.V. Transformer
H.V. Capacitor
H.V. Diode
Magnetron

Check high voltage component according to
component test procedure and replace if it is
defective.

NEW H.V.