R-85STMA (serv.man8). Test Procedures - Sharp Home Appliance Service Manual (repair manual). Page 4

R85STMA

8 – 4

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 - 100M

Ω 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.

The control panel consists of circuits including semiconductors such as LSI, ICs, etc. Therefore, unlike conventional microwave ovens, proper main-
tenance 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 Key Unit, and also the Control unit is divided into two
units, CPU unit and Power unit, and troubleshooting by replacement is described according to the symptoms indicated.

The following symptoms indicate a defective key unit. Replace the key unit.

1) When touching the pads, a certain pad produces no signal at all.

2) When touching a number pad, two figures or more are displayed.

3) When touching the pads, sometimes a pad produces no signal.

The following symptoms indicate a defective control unit. Before replacing the control unit perform the key unit test (Procedure N) to determine if con-
trol unit is faulty.

1) When touching the pads, a certain group of pads do not produce a signal.

2) When touching the pads, no pads produce a signal.

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.

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.

If the display fails to clear when the STOP/CLEAR pad is
depressed, first verify the ribbon 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 flat ribbon cable that connects the key 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 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 a faulty and must be replaced.
If a specific pad does not respond, the above method may be used (after clearing the control unit) to determine if the control unit or key pad is at fault.

CARRY OUT 4R CHECKS.

Table: Resistance of heater

Parts name

Resistance

Grill heating element (Top)

Approximately  59

Ω

Bottom heating element

Approximately 112

Ω

G6

G9

G10

G12

G

11

ROAST

POULTRY

G8

ROAST

PORK

WHOLE

POULTRY

MEAT

JOINT

ROAST BEEF/

LAMB

10sec.

1min.

10min.

G7

G1

G2

G3

G4

G5

CHICKEN

QUARTERS

PIZZA

MORE

GRATIN

PASTA

DISH

BAKED

POTATOES

OVEN

CHIPS

STOP

CLEAR

CHICKEN

QUARTERS

(INSTANT COOK)

START

AUTO

MINUTE

KG/LB

CONVERSION

RISOTTO

UP

KITCHEN

TIMER

GRILL

MICRO

POWER

BREAKFAST

DOWN

info

LESS

DUAL

CONV./

GRILL

CLOCK SET

CONV.

(ºC)