Service Manual for
RCO Speed Oven
34
Power Transformer Test
THE HIGH POTENTIALS AT THE
SECONDARY WINDING OF THE TRANSFORMER
ARE EXTREMELY DANGEROUS. NEVER MAKE ANY
DIRECT VOLTAGE OR CURRENT MEASUREMENTS
ON THIS PART OF THE TRANSFORMER DURING
OR SHORTLY AFTER MAGNETRON OPERATION.
IT IS VERY DANGEROUS TO WORK NEAR THIS
PART WHEN THE OVEN IS ON, OR IF THIS
CIRCUITRY HAS BEEN SWITCHED OFF, AS THE
HV CAPACITOR RETAINS ITS CHARGE EVEN
AFTER DISCONNECTING IT FROM POWER.
THE HIGH VOLTAGE CAPACITOR
RETAINS THE 2.5kV DC CHARGE EVEN
AFTER THE OVEN IS DISCONNECTED. THIS
CAPACITOR MUST BE DISCHARGED BEFORE
WORKING ON ANY COMPONENTS IN THE
HIGH VOLTAGE AREA.
THE POWER TRANSFORMER
MAY HAVE HIGH VOLTAGES PRESENT AT ALL
TIMES EVEN IF THE OVEN IS NOT COOKING.
BE SURE THE OVEN IS ISOLATED BEFORE
TESTING.
Tools Required
• Digital Multimeter
• Insulation Resistance Tester
Procedure
1. Remove the oven from the power source.
HIGH VOLTAGE CAPACITOR MUST
BE DISCHARGED BEFORE THIS PROCEDURE.
WAIT AT LEAST FIVE (5) MINUTES AFTER
SHUTDOWN OF HIGH VOLTAGE SYSTEM.
2. Discharge the high voltage capacitor as described
in the Discharging The High Voltage System section
of this manual.
3. Remove all connections from Power Transformer.
4. Using a digital multimeter, check the resistance of
the windings. Results should be as follows:
a. Primary Winding (208V tap to common and
230V tap to common) 208V Tap 0.89 ± 5% Ω
and 230V Tap 1.01 ± 5% Ω.
b. High Voltage Secondary Winding (Anode tap
to ground) 65.00 ± 5% Ω.
c. Filament Winding (Anode tap to Filament/
Anode tap less than 1Ω.
5. Using an insulation resistance tester or
Megohmmeter, verify the insulation resistance
between the following windings:
a. Primary Winding and Chassis - Pass if over
10 MΩ.
b. Filament winding and chassis - Pass if over
10 MΩ.
Note:
One end of the High Voltage winding is connected
to the transformer stack.
High Voltage Diode Test
THE HIGH POTENTIALS AT THE
HIGH VOLTAGE RECTIFIER ARE EXTREMELY
DANGEROUS. NEVER MAKE ANY DIRECT
VOLTAGE MEASUREMENTS AT THE HIGH
VOLTAGE RECTIFIER CIRCUIT. IT IS VERY
DANGEROUS TO WORK NEAR THIS PART
WHEN THE OVEN IS ON.
THE HIGH VOLTAGE DIODE/
RECTIFIER HAS HIGH VOLTAGES PRESENT
AT ALL TIMES EVEN IF THE OVEN IS NOT
OPERATING. BE SURE THE OVEN IS ISOLATED
BEFORE TESTING.
THE HIGH VOLTAGE CAPACITOR
RETAINS THE 2.5kV DC CHARGE EVEN
AFTER THE OVEN IS DISCONNECTED. THIS
CAPACITOR MUST BE DISCHARGED BEFORE
WORKING ON ANY COMPONENTS IN THE
HIGH VOLTAGE AREA.
Tools required
• Digital Multimeter (true RMS)
• Megohmmeter
Test Procedure
1. Disconnect the oven from the power source.
2. Remove service panel and magnetron cooling
blower to access the high voltage assembly.