33
Service Manual for
RCO Speed Oven
DISCHARGING THE HIGH VOLTAGE SYSTEM
Function
In all common microwave systems utilizing a magnetron,
the microwave energy is generated by a magnetron
vacuum tube. The vacuum tube is driven by a high
voltage DC power supply, which operates at 5kV. The
208V/240VAC line voltage is stepped up to 2.5kVAC
by a high voltage transformer; then connected to a
capacitor-diode rectification circuit that functions as a
voltage doubler.
Location and Access
The high voltage system is located behind the service
panel and magnetron cooling blower and is composed
of two independent electrically identical sets of
components. The high voltage wires are insulated
to withstand a potential of 20kV. They connect all
components of each high voltage system (excluding
grounding), comprising a high voltage transformer, high
voltage capacitor, high voltage diode and magnetron.
The back service panel and magnetron cooling blower
will need to be removed to gain access.
Safety Issues
The high voltage capacitors may retain a lethal charge
after the oven is switched off and both capacitors must
be electrically discharged prior to any work on the high
voltage components and wiring.
THE HIGH VOLTAGE SYSTEM
IS POTENTIALLY DANGEROUS EVEN WHEN
THE POWER IS OFF.
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. REFER TO THE
DISCHARGING THE
HIGH VOLTAGE SYSTEM
SECTION OF THE
MANUAL FOR PROPER INSTRUCTIONS FOR
THIS PROCEDURE.
READ THE INSTRUCTIONS
ON THIS PAGE CAREFULLY, BEFORE YOU
PROCEED.
DUE TO THE HIGH VOLTAGE,
IT IS POSSIBLE TO RECEIVE AN ELECTRIC
SHOCK WHEN TOUCHING A NONMETAL PART
SUCH AS AN INSULATED CONNECTOR OR
CABLE.
Tools Required
• Tool to discharge HV Capacitor (Duke PN: 168775)
• Needle nose pliers with insulated grip to remove
capacitors’ rubber boots and for connecting the
terminals to the capacitor.
High Voltage Capacitor Discharge Procedure
1. The power cord must be completely removed from
the power outlet.
2. WAIT five minutes from time when the HV system
was last powered up. This will permit a partial
discharge through the capacitors’ internal safety
resistors.
CAUTION:
The bleeding resistor might be damaged.
This will prevent the capacitor from
discharging at all.
3. Using insulated pliers to pull back rubber boot from
capacitor terminals.
4. Insert the HV discharge tool into the capacitor so
the prongs simultaneously touch the inside of both
terminals – making sure the tool goes all the way
to the base of the terminals. Repeat steps 3 and 4
on the remaining capacitor. In the event of a large
spark, this means that the internal safety resistor
in the HV capacitor is faulty. After both capacitors
are discharged, remove the defective HV capacitor,
marking it clearly as defective to prevent accidental
re-use. Repeat on the second HV capacitor.
COMPONENT TESTING