R-20A1(S)VN
8 – 2
[2] Procedure B: HIGH VOLTAGE TRANSFORMER TEST
1. CARRY OUT 3D CHECKS.
nections 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 -------------------- 2.8 ohms approximately
b.Secondary winding --------------- 204 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.
3. Also, the high voltage transformer has the thermal cut-out in the primary coil. The thermal cut-out will open when 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 cir-
cuit under normal condition, replace the high voltage transformer because the primary coil (thermal cut-out) has opened. An open primary coil
former, especially the
ventilation opening.
4. CARRY OUT 4R CHECKS.
[3] Procedure C: HIGH VOLTAGE RECTIFIER TEST
CARRY OUT 3D CHECKS.
o its highest range.
d note this second
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 DIRECTION.
[4] Procedure D: HIGH VOLTAGE CAPACITOR TEST
CARRY OUT 3D CHECKS.
1. Isolate the high voltage capacitor from the circuit.
2. Continuity check must be carried out with measuring instrument which is set to the highest resistance range.
3. A normal capacitor shows continuity for a short time (kick) and then a resistance of about 10M after it has been charged.
4. A short-circuited capacitor shows continuity all the time.
5. An open capacitor constantly shows a resistance about 10 M because of its internal 10M resistance.
If incorrect reading are obtained, the high voltage capacitor must be replaced.
CARRY OUT 4R CHECKS.
[5] Procedure E: SWITCH TEST
CARRY OUT 3D CHECKS.
Isolate the switch to be tested and using an ohmmeter check between the terminals as described in the following table.
WARNING:
High voltages and large currents are present at the secondary winding and filament winding of the power transformer. It is
very dangerous to work near this part when the oven is on. NEVER make any voltage measurements of the high-voltage cir-
cuits, including the magnetron filament.
Table: Terminal Connection of Switch
Plunger Operation COM to NO COM to NC COM; Common terminal
Released Open circuit Short circuit
NO; Normally open terminal
Depressed Short circuit Open circuit.
NC; Normally close terminal
1000g
1000g
1000g
T1 C
T2 C
