Sharp R-7H55, Service Manual

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16
R-7H55
TEST PROCEDURES (CONT'D)
PROCEDURE
LETTER
COMPONENT TEST
2. Insulation resistance
Disconnect the wire leads to the heater to be tested. Check the insulation resistance between the
element and cavity using a 500V - 100Mohms insulation tester. The insulation resistance should be
more than 10Mohms in the cold start.
If the results of above test 1 and/or 2 are out of above specifications, the heater is probably faulty and
should be replaced.
CARRY OUT 4R CHECKS
CARRY OUT 3D CHECKS
Disconnect connector-B from the CPU unit. Measure the resistance of the thermistor with an ohmmeter.
Connect the ohmmeter leads to Pin No’s B-5 and B-6 of the thermistor harness.
Room Temp. ......................................... 20˚C - 30˚C
Resistance ..................... Approx. 350 k
Ω
-- 155 k
Ω
If the meter does not indicate above resistance, replace the thermistor.
CARRY OUT 4R CHECKS
J THERMISTOR TEST
K MONITOR RESISTOR TEST
CARRY OUT 3D CHECKS.
Disconnect the leads from the monitor resist. Using an ohmmeter and set on a low range. Check between
the terminals of the monitor resistor.
The resistance of monitor resistor is approx. 0.8 ohms.
If incorrect readings are obtained, replace the monitor resistor.
CARRY OUT 4R CHECKS.
L TOUCH CONTROL PANEL ASSEMBLY TEST
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 two units, Control Unit and Key
Unit, and troubleshooting by 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 Panel
The following symptoms indicate a defective control unit. Before replacing the control unit, perform
the Key unit test (Procedure M) to determine if control unit is 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.