Sharp Carousel R-990C Service Manual - Page 12

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R-990C(S)

Microwave ovens contain circuitry capable of producing very high voltage and current, contact with any part of the

high voltage circuit will result in electrocution. High voltage capacitor, Power transformer, Magnetron, High voltage

rectifier assembly, High voltage harness.

REMEMBER TO CHECK 3D

1) Disconnect the supply.

2) Door opened, and wedged open.

3) Discharge high voltage capacitor.

WARNING: AGAINST THE CHARGE OF THE

HIGH-VOLTAGE CAPACITOR

The high-voltage capacitor remains charged about

60 seconds after the oven has been switched off.

Wait for 60 seconds and then short-circuit the

connection of the high-voltage capacitor (that is, of

the connecting lead of the high-voltage rectifier)

against the chassis with the use of an insulated

screwdriver.

Sharp recommend that wherever possible fault-finding

is carried out with the supply disconnected. It may, in

some cases, be necessary to connect the supply after

the outer case has been removed, in this event carry

out 3D checks and then disconnect the leads to the

primary of the power transformer. Ensure that these

leads remain isolated from other components and the

oven chassis. (Use insulation tape if necessary.) When

the testing is completed carry out 3D checks and

reconnect the leads to the primary of the power trans-

former.

When all service work is completed and the oven is fully assembled, the microwave power output should be

checked and microwave leakage test should be carried out.

When troubleshooting the microwave oven, it is helpful to

follow the Sequence of Operation in performing the

checks. Many of the possible causes of trouble will require

that a specific test be performed. These tests are given a

procedure letter which will be found in the "Test Procedure

"section.

SERVICING

WARNING TO SERVICE PERSONNEL

TROUBLESHOOTING GUIDE

REMEMBER TO CHECK 4R

1) Reconnect all leads removed from components

during testing.

2) Replace the outer case (cabinet).

3) Reconnect the supply.

4) Run the oven. Check all functions.

Microwave ovens should not be run empty. To test for

the presence of microwave energy within a cavity,

place a cup of cold water on the oven turntable, close

the door and set the microwave timer for two (2)

minutes. Set the power level to HIGH and push the

START button. When the two minutes has elapsed

(timer at zero) carefully check that the water is now hot.

If the water remains cold carry out 3D checks and re-

examine the connections to the component being

tested.

IMPORTANT: If the oven becomes inoperative because

of a blown fuse M8A in the upper latch

switch - lower latch switch - monitor switch

- monitor resistor circuit, check the upper

latch switch, lower latch switch, monitor

switch and monitor resistor before replac-

ing the fuse M8A.