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R-249(SL)
R-249(W)
8
TEST PROCEDURES
PROCEDURE
LETTER
COMPONENT TEST
B
C
HIGH VOLTAGE RECTIFIER
B
HIGH VOLTAGE TRANSFORMER TEST
WARNING: High voltage and large currents are present at the secondary winding and
filament winding of the high voltage transformer. It is very dangerous to work
near this part when the oven is on. NEVER make any voltage measurements
of the high-voltage circuits, including the magnetron filament.
near this part when the oven is on. NEVER make any voltage measurements
of the high-voltage circuits, including the magnetron filament.
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:-
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 .......................... 3.3 ohms approximately
b. Secondary winding .................... 207 ohms approximately
c. Filament winding ..................................... less than 1 ohm
b. Secondary winding .................... 207 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.
faulty and should be replaced.
3. Also, the high voltage transformer has the thermal cut-out 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 thermal cut-out in the primary coil reaches approximately 150˚C. The
thermal cut-out resets automatically at 130˚C. If an ohmmeter indicates an open circuit under
normal condition, replace the high voltage transformer because the primary coil (thermal cut-out)
has opened. An open primary coil (thermal cut-out) indicates overheating of the high voltage
transformer. Check for restricted air flow to the high voltage transformer, especially the ventilation
opening.
the temperature of the thermal cut-out in the primary coil reaches approximately 150˚C. The
thermal cut-out resets automatically at 130˚C. If an ohmmeter indicates an open circuit under
normal condition, replace the high voltage transformer because the primary coil (thermal cut-out)
has opened. An open primary coil (thermal cut-out) indicates overheating of the high voltage
transformer. Check for restricted air flow to the high voltage transformer, especially the ventilation
opening.
4. CARRY OUT 4R CHECKS.
C
HIGH VOLTAGE RECTIFIER ASSEMBLY TEST
HIGH VOLTAGE RECTIFIER TEST
CARRY OUT 3D CHECKS.
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 B+C 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
using an ohmmeter set to its highest range. Connect the ohmmeter across the terminal B+C 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.
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, BE-
CAUSE OTHERWISE AN INFINITE RESISTANCE MIGHT BE SHOWN IN BOTH DIREC-
TIONS.
CAUSE OTHERWISE AN INFINITE RESISTANCE MIGHT BE SHOWN IN BOTH DIREC-
TIONS.
D
HIGH VOLTAGE CAPACITOR TEST
CARRY OUT 3D CHECKS.
A. Isolate the high voltage capacitor from the circuit.
B. Continuity check must be carried out with measuring instrument which is set to the highest
B. Continuity check must be carried out with measuring instrument which is set to the highest
resistance range.
C. A normal capacitor shows continuity for a short time (kick) and then a resistance of about 10M
Ω
after it has been charged.
D. A short-circuited capacitor shows continuity all the time.
E. An open capacitor constantly shows a resistance about 10 M
E. An open capacitor constantly shows a resistance about 10 M
Ω because of its internal 10MΩ
resistance.
F. When the internal wire is opened in the high voltage capacitor shows an infinite resistance.
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