R-890SLM
[12] L: GRILL HEATING ELEMENTS (TOP) AND BOTTOM HEATING ELEMENT TEST
CARRY OUT 3D CHECKS.
Before carrying out the following tests make sure the heating element is cool completely.
1. Resistance of heater.
Disconnect the wire leads to the heating element to be tested. Using ohmmeter with low resistance range. Check the resistance
across the terminals of the heating element as described in the following table.
Table: Resistance of heater
Parts name
Resistance
Grill heating element (Top)
Approximately 48
Bottom heating element
Approximately 92Ω
2. Insulation resistance.
Disconnect the wire leads to the heating element to be tested. Check the insulation resistance between the element terminal and
cavity using a 500V - 100MΩ insulation tester. The insulation resistance should be more than 10MΩ in the cold start.
If the results of above test 1 and/or 2 are out of above specifications, the heating element is probably faulty and should be replaced.
CARRY OUT 4R CHECKS.
[13] M: CONTROL PANEL ASSEMBLY TEST
The control panel consists of circuits including semiconductors such as LSI, ICs, etc. Therefore, unlike conventional microwave ovens,
proper maintenance can not be performed with only a voltmeter and ohmmeter.
In this service manual, the control panel assembly is divided into two units, Control Unit and Jog switch Unit, and troubleshooting by
replacement is described according to the symptoms indicated.
1. Jog switch Unit Note: Check Jog switch unit wire harness connection before replacement.
The following symptoms indicate a defective Jog switch unit. Replace the Jog switch unit.
1.1. Tact switch
1) When touching the buttons, a certain button produces no signal at all.
2) When touching the buttons, sometimes a button produces no signal.
1.2. Potentiometer
1) When rotating the potentiometer, the cooking mode can not be selected.
1.3. Encoder
1) When rotating the encoder, the cooking time or the weight of food can not be entered.
2. Control Panel
The following symptoms indicate a defective control unit. Before replacing the control unit, perform the Jog switch unit test (Procedure N)
to determine if control unit is faulty.
2.1. In connection with buttons
1) When touching the buttons, a certain group of buttons do not produce a signal.
2) When touching the buttons, no buttons produce a signal.
2.2. In connection with indicators
1) At a certain digit, all or some segments do not light up.
2) At a certain digit, brightness is low.
3) Only one indicator does not light up.
4) The corresponding segments of all digits do not light up; or they continue to light up.
5) Wrong figure appears.
6) A certain group of indicators do not light up.
7) The figure of all digits flicker.
2.3. Other possible troubles caused by defective control unit.
1) Buzzer does not sound or continues to sound.
2) Clock does not operate properly.
3) Cooking is not possible.
4) Proper temperature measurement is not obtained.
[14] N: JOG SWITCH UNIT TEST
If the display fails to clear when the STOP button is depressed, first verify the cable is making good contact, verify that the stop switch
operates properly; that is the contacts are closed when the door is closed and open when the door is open. If the stop switch is good,
disconnect the cable that connects the Jog switch unit to the control unit and make sure the stop switch is closed (either close the
door or short the stop switch connector). Use the Jog switch unit matrix indicated on the control panel schematic and place a jumper
wire between the pins that correspond to the STOP button making momentary contact. If the control unit responds by clearing with a
beep the Jog switch unit is faulty and must be replaced. If the control unit does not respond, it is a faulty and must be replaced. If a
specific button does not respond, the above method may be used (after clearing the control unit) to determine if the control unit or Jog
switch unit is at fault.
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