Servicing - Sharp R-240B Service Manual

R-240B
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 transformer.
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 proce-
dure letter which will be found in the "Test
Procedure"section.

SERVICING

WARNING TO SERVICE PERSONNEL
TROUBLESHOOTING GUIDE
6
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 power level to HIGH. And set the
microwave timer for two (2) minutes. 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 1st. latch switch
- 2nd. latch switch - relay RY2 - monitor
switch - monitor resistor circuit, check the
1st. latch switch, 2nd. latch switch, moni-
tor switch, relay RY2 and monitor resistor
before replacing the fuse M8A.