Sharp R-4H56, Service Manual

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R-4H56
14
TEST PROCEDURES (CONT'D)
PROCEDURE
LETTER
COMPONENT TEST
I BLOWN FUSE F M8A
CARRY OUT 3D CHECKS.
1. If the fuse M8A is blown, there could be shorts or ground in electrical parts or wire harness.
Check them and replace the defective parts or repair the wire harness.
2. If the fuse M8A is blown when the door is opened, check the upper latch switch, lower latch switch,
monitor switch and monitor resistor.
If the fuse M8A is blown by incorrect door switching replace the defective switch(s) and the fuse M8A.
3. If the fuse M8A is blown, there could be a short in the asymmetric rectifier or there could be a ground
in wire harness. A short in the asymmetric rectifier may have occurred due to short or ground in H.V.
rectifier, magnetron, power transformer or H.V. wire. Check them and replace the defective parts or
repair the wire harness.
CARRY OUT 4R CHECKS.
CAUTION: ONLY REPLACE FUSE M8A WITH THE CORRECT VALUE REPLACEMENT
The touch control panel consists of circuits including semiconductors such as LSI, ICs, etc. Therefore,
unlike conventional microwave ovens, proper maintenance cannot be performed with only a voltmeter
and ohmmeter. In this service manual, the touch control panel assembly is divided into troubleshooting
by unit replacement is described according to the symptoms indicated.
1. Key Unit. Note : Check key unit ribbon connection before replacement.
The following symptoms indicate a defective key unit. Replace the key unit.
a) When touching the pads, a certain pad produces no signal at all
b) When touching a number pad, two figures or more are displayed.
c) When touching the pads, sometimes a pad produces no signal.
2. Control Unit
The following symptoms indicate a defective control unit. Before replacing the control unit, perform
the key unit test to determine if control units faulty.
2-1 In connection with pads.
a) When touching the pads, a certain group of pads do not produce a signal.
b) When touching the pads, no pads produce a signal.
2-2 In connection with indicators
a) At a certain digit, all or some segments do not light up.
b) At a certain digit, brightness is low.
c) Only one indicator does not light.
d) The corresponding segments of all digits do not light up; or they continue to light up.
e) Wrong figure appears.
f) A certain group of indicators do not light up.
g) The figure of all digits flicker.
2-3 Other possible troubles caused by defective control unit.
a) Buzzer does not sound or continues to sound.
b) Clock does not operate properly.
c) Cooking is not possible.
d) Proper temperature measurement is not obtained.
J TOUCH CONTROL PANEL ASSEMBLY TEST
K KEY UNIT TEST
If the display fails to clear when the STOP/CLEAR pad is depressed. first verify the ribbon is making good
contact, verify that the door sensing switch (stop switch) operates properly; that is the contacts are closed
when the door is closed and open when the door is open. If the door sensing switch (stop switch) is good,
disconnect the flat ribbon that connects the key unit to the control unit and make sure the door sensing
switch is closed (either close the door or short the stop switch connecter). Use the key unit matrix
indicated on the control panel schematic and place a jumper wire between the pins that correspond to
the STOP/CLEAR pad making momentary contact. If the control unit responds by clearing with a beep,
the key unit is faulty and must be replaced. If the control unit does not respond, it is faulty and must be