Specifications

Ver SG 9/200 30 Sharp Electronics Corporation
CONTROL SECTION
The controls which are used in microwave ovens vary from oven to oven.
The mechanical timer control is used in models R-200BK, R-200BW, R-300BW and the
R-21HC. Refer to the wiring diagram section of this manual for the following
description.
The mechanical timer has two basic designs. The first is a simple motor and a single
switch. The timer dial, when turned, will cause the contacts of the timer switch to close.
As the switch contacts close they will complete the parallel circuit to the oven light, fan
motor, turn table motor, timer motor, and power transformer. Once the motor starts to
turn it will continue until it mechanically opens the timer switch contacts. This will open
the parallel circuit terminating all oven functions.
To diagnose the mechanical timer, unplug the unit, disconnect the power supply and
check continuity across the switch contacts. When the timer is in the off position an
infinite reading should be indicated on the meter. When the dial timer is turned to any on
position, zero ohms or continuity should be indicated. If the timer switch checks good,
restore power to the unit and turn the timer dial to close the switch contacts. With a volt
meter check for 120 volts across the motor terminals directly. A reading of 120 volts
should be indicated. If the voltage is present but the timer doesn’t operate, replace the
timer.
The second mechanical timer design has a second switch for the defrost function. The
switch is normally opened and closed by a cam that turns within the timer assembly. The
switch is located in series with the power transformer, therefore only affecting the
transformer operation as it opens and closes.
To diagnose the switch the oven must be operating. A voltage check across the defrost
switch must be taken. When the meter indicates 120 volts the switch is open. When the
meter indicates zero volts the switch is closed. If the meter fails to detect the switch
either opening or closing, replace the switch and/or the timer assembly depending on the
reason for the failure of the switch activation.
All other ovens utilize a solid state control. The control is an assembly which is
comprised of a key unit and a control unit. Refer to the Control Panel Circuit Operation
on the next page for the following explanation.