Sharp R-22JT User manual

Sharp Electronics Corporation
Servicing
Commercial
Microwave Ovens
R21JC/21HT &
R22GTF/R22JT

Len Hahn
Senior Manager, Field Services &
Support
These ovens should not be adjusted or
repaired by anyone except properly
qualified service personnel.

Objective
This course has been designed around the
R22JT Commercial Microwave Oven. All
disassembly and testing procedures refer to the
R22JT only. While most heavy duty ovens are
quite similar please refer to the specific model
you are working on.
Your have information on all four models, R21
series and R22 series.

Microwave Technologies Quiz
1. What is Microwave energy?
a. Energy created by nuclear radiation.
b. Energy created by chemical reaction.
c. Energy created by electromagnetic generation
d. Energy created by atomic fusion
2. What is the frequency at which the magnetron operates?
a. 60 Hz
b. 60KHz
c. 2450KHz
d. 2450MHz

Microwave Technologies Quiz
3. Microwave energy cooks food from
a. from the outside to the inside
b. from the inside to the outside.
c. only from the top.
d. only from the bottom.
4. Why does food sometimes appear to cool faster when cooked in a
microwave than when cooked in a conventional oven?
a. Microwave energy does not last as long in certain foods and allows
heat to escape.
b. Because microwave ovens cook faster, the food load cools faster.
c. Microwave cooking utensils do not get hot, so they draw heat from the
food.
d. Microwave energy is not as powerful as gas or electric heat energy.

Microwave Technologies Quiz
5. When the microwave recipe calls for a "let stand" time, what is this
allowing for?
a. The microwave to escape from the food.
b. Allows the food to cool before eating.
c. Allows the cooking container to cool before handling.
d. Allows the food to finish cooking.
6. When can metal be used inside a microwave oven?
a. When you want the food not to over cook.
b. When you want to generate more heat.
c. When you want to protect your oven from cooking splatters.
d. Never use metal in a microwave oven.

Microwave Technologies Quiz
7. When working on a microwave oven with the cabinet removed, the
technician is exposed to a lethal danger. What is the danger?
a. The high voltage and current potentials even when power is
removed.
b. Radiation energy.
c. The high electrical resistance within the electrical circuits even
when power is removed.
d. The high wattage output from the magnetron.
8. When working on a microwave after disconnecting the power cord from
the outlet and removing the cabinet, the technician must:
a. discharge the high voltage capacitor
b. check the magnetron.
c. check the fuse.
d. check the door for RF leakage.

Microwave Technologies Quiz
9. How often must a microwave oven be tested for leakage?
a. Anytime after service.
b. Only if the customer complains of headaches.
c. Only if the door or door switches are repaired.
d. Only if the magnetron is replaced.
10. To comply with the law, what is the maximum amount of leakage
allowed to be emitted from a microwave oven?
a. 1 milliwatt per square centimeter.
b. 3 milliwatt per square centimeter.
c. 5 milliwatt per square centimeter.
d. 7 milliwatt per square centimeter.

R-21JCA Control Panel 1000 Watts

R-21JCA Oven diagram
Rotary antenna
Ceramic shelf Air intake openings
Air ventilation cover and openings

R-21JCA Ceramic Shelf Removal
Using a putty knife, lift
up from underneath the
ceramic shelf to remove
shelf from cavity. Be
careful not to damage
the rubber fins.
Rubber fins
No rubber fin

R-21JCA Ceramic Shelf Installation
Rubber fins
No rubber fin
Position the front of the shelf
with the front of the oven. The
front edge of the shelf does not
have a rubber fin.
Push down on the rear of the
shelf to complete the
installation taking care not to
damage the rubber fins.

R-21JCA Schematic

Transformers
•Transformers can be used to step-up or
step-down an applied AC voltage
•The High Voltage transformers that are
used in microwave ovens are the step up
type
•The 22JT employs two 1:20 step up
transformer which outputs 20 volts for
every volt applied to the primary
•When we apply 120 volts to the HV
transformer primary, 2400 volts will be
available at the secondary
Primary
Secondary
Input=
120 volts
Output=
2400 volts

Transformers
•Secondary current is inversely
proportional to the turns ratio
•Available output current in our 1:20
step up transformer will be 20x less
than the current on the primary
•The high voltage doubler circuit will
double the transformer secondary
voltage to 4800 volts with an output
current between 300ma and 450ma
•This 2400volt potential at 300ma is
enough to kill you if came into contact
with it.
Primary
Secondary
Input=
8 amps
Output=
400 ma

Danger

Electrocution

R-21JCA Single Magnetron

High Voltage Doubler Operation

High Voltage Doubler Operation
Doubler charging Doubler Discharging “Voltage Adding”