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R-254M - 10
TEST PROCEDURES
PROCEDURE
LETTER
COMPONENT TEST
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.
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.
CARRY OUT 3D CHECKS.
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:-
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 .......................... 2.2 ohms approximately
b. Secondary winding .................... 140 ohms approximately
c. Filament winding ..................................... less than 1 ohm
b. Secondary winding .................... 140 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.
CARRY OUT 4R CHECKS.
and should be replaced.
CARRY OUT 4R CHECKS.
C
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 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
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 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, BECAUSE
OTHERWISE AN INFINITE RESISTANCE MIGHT BE SHOWN IN BOTH DIRECTIONS.
OTHERWISE AN INFINITE RESISTANCE MIGHT BE SHOWN IN BOTH DIRECTIONS.
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 10M
Ω
resistance.
F. When the internal 10 M
Ω
is opened in the high voltage capacitor, the capacitor shows an infinite
resistance.
G. The resistance across all the terminals and the chassis must be infinite when the capacitor is normal.
If incorrect reading are obtained, the high voltage capacitor must be replaced.
If incorrect reading are obtained, the high voltage capacitor must be replaced.
CARRY OUT 4R CHECKS.
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