DOWNLOAD Sharp R-85STMA (serv.man8) Service Manual ↓ Size: 224.41 KB | Pages: 5 in PDF or view online for FREE

R85STMA

8 – 3

If incorrect readings are obtained, replace the thermal cut-out.

An open circuit thermal cut-out (MG) indicates that the magnetron has overheated, this may be due to resistricted ventilation, cooling fan failure.

An open circuit thermal cut-out (OVEN) indicates that the oven cavity has overheated, this may be due to no load operation, or excessive heat / fire
inside the oven.

CARRY OUT 4R CHECKS.

CARRY OUT 3D CHECKS.

Disconnect the leads from the motor. Using an ohmmeter, check the resistance between the two terminals as described in the table below.

If incorrect readings are obtained, replace the motor.

CARRY OUT 4R CHECKS.

CARRY OUT 3D CHECKS.

Disconnect the leads from the terminals of the noise filter. Using an ohmmeter, check
between the terminals as described in the following table. 

If incorrect readings are obtained, replace the noise filter unit.

CARRY OUT 4R CHECKS.

CARRY OUT 3D CHECKS.

If the fuse 20A is blown, there is a shorts or grounds in electrical parts or wire harness. Check them and replace the defective parts or repair the wire
harness.

CARRY OUT 4R CHECKS.

CAUTION: Only replace fuse with the correct value replacement.

CARRY OUT 3D CHECKS.

1. If the fuse F8A is blown when the door is opened, check the monitored latch switch and monitor switch.

2. If the fuse F8A is blown by incorrect door switching replace the defective switch(es) and the noise filter (fuse F8A).

3. If the fuse F8A is blown, there could be shorts in the asymmetric rectifier or there is a ground in wire harness. A short in the asymmetric rectifier

may be occurred due to short or ground in H.V. rectifier, magnetron, high voltage transformer or H.V. wire. Check them and replace the defective
parts or repair the wire harness.

CARRY OUT 4R CHECKS.

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 termi-
nals of the heating element as described in the following table.

Table: Thermal Cut-out Test

Parts Name

Temperature of “ON” condition 

(closed circuit).

Temperature of “OFF” condition 

(open circuit).

Indication of ohmmeter (When room 
temperature is approx. 20

°C.)

Thermal cut-out 125

°C

This is not resetable type.

Above 125

°C

Closed circuit

Thermal cut-out 150

°C

Bellow 130

°C.

Above 150

°C

Closed circuit

Table: Resistance of Motor

Motors

Resistance

Fan motor

Approximately   399

Ω

Turntable motor

Approximately 14.7k

Ω

Convection fan motor

Approximately  288k

Ω

MEASURING POINT 

INDICATION OF OHMMETER

Between N and L 

Approx. 680 k

Ω

Between terminal N and WHITE 

Short circuit

Between terminal L and RED 

Short circuit

F8A

20A

WHT

RED

R1

R2

N

Cx

Cy

L

L

L

L (min) Cx ± 20% Cy ± 20%

R1

R2

1.0mH

0.22 uF

4700pF 10 M

680k

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)

R85STMA

8 – 5

CARRY OUT 3D CHECKS.

Remove the outer case and check voltage between Pin Nos. 1 and 3 of the 4 pin connector (E) on the control unit with an A.C. voltmeter. The meter
should indicate 230-240 volts, if not check oven circuit.

Relay Test

Check voltage at the relay coil with a D.C. voltmeter during the microwave cooking operation, grill operation, convection operation or dual operation.

        DC. voltage indicated ................................... Defective relay.

        DC. voltage not indicated ............................. Check diode which is connected to the relay coil. If diode is good, control unit is defective.

CARRY OUT 4R CHECKS.

Problem: POWER ON, indicator does not light up.

CARRY OUT 3D CHECKS.

NOTE: *At the time of these repairs, make a visual inspection of the varistor for burn-

ing damage and examine the transformer with tester for the presence of layer
short circuit (check primary coil resistance).

If any abnormal condition is detected, replace the control unit.

CARRY OUT 4R CHECKS.

RELAY SYMBOL

OPERATIONAL VOLTAGE

CONNECTED COMPONENTS

RY1

APPROX. 18.0V D.C.

Oven lamp / Turntable motor

RY2

APPROX. 18.0V D.C.

High voltage transformer

RY3

APPROX. 24.0V D.C.

Grill (Top) heating element

RY4

APPROX. 24.0V D.C.

Bottom heating element

RY5

APPROX. 24.0V D.C.

Touch control transformer

RY6

APPROX. 24.0V D.C.

Fan motor

RY7

APPROX. 24.0V D.C.

Convection motor

STEPS

OCCURRENCE

CAUSE OR CORRECTION

1

The rated AC voltage is not present between Pin Nos. 1 and 3 of the 4-
pin connector (E).

Check supply voltage and oven power cord.

2

The rated AC voltage is present at primary side of low voltage trans-
former.

Low voltage transformer or secondary circuit defective.
Check and replace the touch control transformer or control unit.

3

Only pattern at “a” is broken.

*Insert jumper wire J1 and solder. 
(CARRY OUT 3D CHECKS BEFORE REPAIR)

4

Pattern at “a” and “b” are broken.

Replace the control unit. 
(CARRY OUT 3D CHECKS BEFORE REPAIR)

CN-A

CN-E

D12

7

(J1)

D13

VRS1

R85STMA

8 – 5

CARRY OUT 3D CHECKS.

Remove the outer case and check voltage between Pin Nos. 1 and 3 of the 4 pin connector (E) on the control unit with an A.C. voltmeter. The meter
should indicate 230-240 volts, if not check oven circuit.

Relay Test

Check voltage at the relay coil with a D.C. voltmeter during the microwave cooking operation, grill operation, convection operation or dual operation.

        DC. voltage indicated ................................... Defective relay.

        DC. voltage not indicated ............................. Check diode which is connected to the relay coil. If diode is good, control unit is defective.

CARRY OUT 4R CHECKS.

Problem: POWER ON, indicator does not light up.

CARRY OUT 3D CHECKS.

NOTE: *At the time of these repairs, make a visual inspection of the varistor for burn-

ing damage and examine the transformer with tester for the presence of layer
short circuit (check primary coil resistance).

If any abnormal condition is detected, replace the control unit.

CARRY OUT 4R CHECKS.

RELAY SYMBOL

OPERATIONAL VOLTAGE

CONNECTED COMPONENTS

RY1

APPROX. 18.0V D.C.

Oven lamp / Turntable motor

RY2

APPROX. 18.0V D.C.

High voltage transformer

RY3

APPROX. 24.0V D.C.

Grill (Top) heating element

RY4

APPROX. 24.0V D.C.

Bottom heating element

RY5

APPROX. 24.0V D.C.

Touch control transformer

RY6

APPROX. 24.0V D.C.

Fan motor

RY7

APPROX. 24.0V D.C.

Convection motor

STEPS

OCCURRENCE

CAUSE OR CORRECTION

1

The rated AC voltage is not present between Pin Nos. 1 and 3 of the 4-
pin connector (E).

Check supply voltage and oven power cord.

2

The rated AC voltage is present at primary side of low voltage trans-
former.

Low voltage transformer or secondary circuit defective.
Check and replace the touch control transformer or control unit.

3

Only pattern at “a” is broken.

*Insert jumper wire J1 and solder. 
(CARRY OUT 3D CHECKS BEFORE REPAIR)

4

Pattern at “a” and “b” are broken.

Replace the control unit. 
(CARRY OUT 3D CHECKS BEFORE REPAIR)

CN-A

CN-E

D12

7

(J1)

D13

VRS1