Sharp R-4A52 Service Manual page 6

R-4A52
R-4E52
MEDIUM HIGH, MEDIUM, MEDIUM LOW,
SETTING
LOW COOKING
When the microwave oven is preset for variable cook-
ing power, 240 volts A.C. power is supplied to the
power transformer intermittently within a 32-second
time base through the'relay contact which is coupled
with the current-limiting relay RY2.
The following
levels of microwave power are given.
HIGH
MEDIUM HIGH
MEDIUM
MEDIUM LOW
LOW
32 sec. ON
24 sec. ON 8 sec. OFF
-1 Approx. 70% = 525 Watts
lEsac.ON 14 sec. OFF
m-1 Approx. 50% = 375 Watts
12secON 20 sec. OFF
m-1 Approx. 30% = 225 Watts
6 sec. ON 26 sac. OFF
m------j Approx. 10% = 75 Watts
NOTE: The ON/OFF time ratio does not exactly corre-
I
spond to the percentage of microwave power,
because approx. 2 seconds are needed for
heating up the magnetron filament.
FUNCTION OF IMPORTANT COMPONENTS
DOOR OPEN MECHANISM
The door can be opened by pushing the door open
button on the control panel. When the door open
button is pushed, the latch lever is moved upward,
operating the latch head. The latch head is moved
upward, and released from the latch hook. Now, the
door can be opened.
.LATCH MONITOR
HOOK \
, SWITCH
DOOR
LATCH
HEAD
KE
SWITCH
I
-. -.
SWITCH
LOWER
kGGON~ L -s-w:T:! _ _ /
--7
Figure D-l. Door Open Mechanism
UPPER LATCH SWITCH SW1
LOWER LATCH SWITCH SW2
STOP SWITCH SW4
1. When the oven door is closed, the contacts
(COM - NO) must be closed.
2. When the oven door is opened, the contacts
(COM - NO) must be opened.
M'ONITOR SWITCH SW3
1. When the oven door is closed, the contacts
(COM- NC) must be opened.
2. When the oven door is opened, the contacts
(COM - NC) must be closed.
3. If the oven door is opened and the contacts
(COM - NO) of the upper and lower latch switches
SW1 + SW2 fail to open, the fuse E M8A blows si-
multaneously with closing the contacts (COM- NC)
of the monitor switch SW3
CAUTION: BEFORE REPLACING A BLOWN FUSE F
M8A TEST THE UPPER AND LOWER
LATCH SWITCHES SW1 + SW2 MONI-
TOR SWITCH SW3 AND MONITOR RE-
SISTOR FOR
OPERATlON.(:EFER TO
PROPER
CHAPTER
"TEST PROCEDURE".)
MONITOR RESISTOR- R 0.8 Q 20W
The monitor resistor prevents the fuse E M8A bursting
when the fuse E M8A blows due to the operation of
the monitor switch.
THERMAL CUT-OUT TC 145°C (OVEN)
The thermal cut-out located on the top of the oven
cavity is designed to prevent damage to the oven if the
foods in the oven catch fire due to over heating
produced by unproper setting of cook time or failure
of control unit.
Under normal operation, the oven thermal cut-out re-
mains closed. However, when abnormally high tem-
peratures are reached within the oven cavity, the oven
thermal cut-out will open at 145"C, causing the oven
to shut down.
The thermal cut-out TC will be close its contacts again
when its temperature goes down lower than -20°C.
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