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MICROWAVE OVEN MODELS R-420BK / R

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1. amp NO SS 2 S E YOUMS I Buisu s 05 N LHM See esn Jo1Uuo A ueAQ Le Pe P CH 10H L Een 37 R 420BK R 420BW LD1 LD5 LD1 LD2 LD3 LD4 LD5 fS i Y ek Py al O O WH 1 Q3 KRC243M C5 O J2 G O NOTE w IF NOT SPECIFIED 1 4w 5 NOT SPECIFIED 1SS270A Power Unit Circuit 38 Lg sch 0 1 50 pas C4 10y 35v E G zs A NO C VR 17 Q2 2581238 D1 D4 T 4 ps 06 8547 d 3 3 1 6 y On Sq VRO 3 2SB1238 R2 680 1 2w SC TURNTABLE Er MOTOR OVEN LAMP FAN MOTOR AC MICRO O O O gt EE drum EE EE H 5 N GND BUZZER TURNTABLE MOTOR OVEN LAMP FAN MOTOR MICRO P DOOR SWITCH d R 420BK R 420BW 301 eau 192014 31091 6018 SE ae ee 39096 20184 Dm Ti E SES THs Hes Hrs HsH vol 85 D 5 E gt amp Q vureztvig VMeSLVIN oun x ssp Ar 220 220 HOLMS S BEE Se um E qum TE BE 29 EH CE 512041 3 1
2. This is the basic timing for time processing of LSI H 5V f L GND i 16 7 msec gt i UT Temmalmoused FmY Connected to VC Auto clear terminal LE Signal similar to P46 INTO 4 3 When either GOO9 line on key matrix is touched a corresponding signal will be inputted into P43 Signal synchronized with commercial power source frequency P41 IN Signal is input to reset the LSI to the initial state when power is supplied Temporarily set to L level the moment power is supplied at this time the LSI is reset Thereafter set at H level Terminal not used RESET 28 29 P70 P71 O X IN U T 22 23 24 25 26 27 30 Internal clock oscillation frequency setting input The internal clock frequency is set by applying the ceramic filter oscillatior circuit with respect to XIN terminal OUT Internal clock oscillation frequency control output Output to control oscillation input of XOUT 31 XOUT VSS Power source voltage 5V VC voltage of power source circuit input P27 OUT Key strobe signal Signal applied to touch key section A pulse signal is inputted to P43 P46 terminal while one of G8 line keys on key matrix is touched P26 OUT Key strobe signal Signal applied to touch key section A pulse signal is inputted to P43 P46 terminal while one of G7 line keys on key matrix is touched P25 OUT Key st
3. 0 8 0 r 2935129 eif sa 4 99 DEE E E 223525 HdS98VZl 1 21 EE SLOLVHM el e 11935166 ou ony 1 1 Roses 3193545 50 uazzna ES Seege ES 5922 Gurt DIN gt eo Io Sa AGE Si0ivB 1 75 IN f Sh o 2 o D Q HIE e e e TTE Te To To T 9 NE 5 RER 5 E 43 5 581 HOSN3S 70092 29 NIA M i e IAN IN IN 9 OALUOD AGZ 100 031510395 LON 31 3 HOSN3S HV 55655 031510345 LON 31 M K 2 S MOL L 0315192385 LON 31 vv ALON LINN umu 4504339 sdoyo VM 200 XGL 89H 32g 39 gt KS KH Po R 420BK R 420BW Printed Wiring Board of Power Uni R 420BK R 420BW PARTS LIST Contact your nearest SHARP Parts Distributor to order For location of SHARP Parts Distributor Please call Toll Free 1 800 BE SHARP RefNo PartNo 8 Description Code RC QZB018MREO FH DZBOOSMRYO QSOCLBOO6MREO RLMPTA03 OWREO H V Capacitor H V Diode assembly
4. Hold the chassis support to the magnetron and mag netron duct with one 1 screw 4 Connect wire leads to the magnetron 5 Re install outer case and check that the oven is oper ating properly CAUTION When replacing the magnetron be sure that the R F gasket is in place and that the mounting screws are tightened securely RDA1305U Control Panel Assembly Removal 1 Disconnect the power supply cord and remove outer case cabinet Open the oven door and block it open Discharge high voltage capacitor Disconnect wire leads from panel components Remove the one 1 screw holding the control panel Re adjust the clip holding panel assembly to oven flange Remove control panel assembly by sliding it upward Now individual components can be removed D P 1 Before attaching new key unit remove remaining adhesive on the control panel frame surface com pletely with alcohol 2 When attaching the key unit to the control panel frame adjust the upper edge and right edge of the key unit to the correct position of the control panel 3 Stick the key unit firmly to the control panel frame by rubbing with soft cloth Oven Lamp and Lamp Socket Removal 1 Disconnect the power supply cord and remove outer case cabinet Open the oven door and block it open Discharge high voltage capacitor Pull the wire leads from the oven lamp socket with the flat type small
5. 41 R 420BK R 420BW Panno 8 6 Control Panel CPWBFBOOSMRUO Control unit 4 QCNCMA394DREO OCNCMA275DREO QCNCMA422DREO FW VZB141MREO di W mW 2 pin connector CN A 2 pin connector CN B gt 00 9 pin connector CN C P d Lead wire harness WH 1 gt RC KZA087DREO D D Capacitor 0 1uF 50V C2 VCEAB31EW108M Capacitor 1000uF 35V AD C3 RC KZA087DREO Capacitor 0 1uF 50V AB 4 5 VCEAB31VW106M Capacitor 10uF 35V AB D1 4 VHD11ES1 1 Diode 11ES1 AB VHD1SS270A 1 VHPSLZ381A9 3 VS2SB1238 3 VSKRC243M 3 VRD B12EF242J Diode 1SS270A Light emitting diode Transistor 2SB1238 Transistor KRC243M Resistor 2 4kQ 1 ag gt VRD B12HF681J Resistor 6800 1 51 R3 VRD B12HF511J Resistor 5100 1 5w AB RA VRD B12bEF270J Resistor 270 1 41 AA R5 VRD B12bEF472J Resistor 4 7kQ 1 W AA R6 VRD B12EF332J Resistor 3 3kQ 1 41 AA RRLY A075DRE0 RRLY B002MRE0 RALM A014DRE0 RTRNPBOO9MREO RH VZAO32DREO Relay OJE SS 124LM Relay DU24D1 1P M Buzzer PKM22EPT o m Q Transformer Varistor 104G471K VHEHZ161 1 LHLD B004MRFO FPNLCB202MRKO FPNLCB203MRKO FUNTKB150MREO Zener diode HZ16 1 LED holder Control panel assembly R 420BK Control panel assembly R 420BW Key unit R 420BK GEES dnm voc de c XA Ee G
6. Oven lamp socket Oven lamp RMOTEA3 46WREO Fan motor 1 AQ 1 AM 1 AE 1 AE 1 AR QFSHDB003MRE0 FFS BA016 KIT Fuse block Monitor switch V 16G 2C25 amp Fuse assembly 20A 250VAC QSW MA110WREO QFS TBO06MREO Sec interlock amp Door sensing switch V 16G 3C25 144 C Temperature fuse RV MZA255WREO RMOTDA182 KIT Magnetron T T Motor RTRN BO60MREO Power transformer FACCDBOO3MREO QW OZBO016MREO Power cord P PR H V wire A Transformer Capacitor FW VZB147MREO FW VZB125MREO Main wire harness Stop switch harness P P FDTCTA177WRKO AH sensor 5 GE 8 8 R SS e ARA LBNDKB007MRPO LANGTB028MRPO PHOK BO13MRFO GDAI B050MRPO GLEGPBOO3MRFO H V Capacitor band Chassis support Latch hook Base plate Foot MLEVPBO016MRFO Latch lever PDUC BO73MRPO NFANPBOOIMREO PDUC B043MRFO Magnetron duct Fan blade Fan duct Oven cavity Not a replaceable part PCOVPBO037MRPO Waveguide cover GCABUBO64MRPO Outer case cabinet R 420BK GCABUBO58MRPOA Outer case cabinet R 420BW FROLPB024MRKO T T Roller assembly NTNT AO095WREO T T Tray PPACGBO14MRFO T T Motor packing PCUSGBO033MRPO Base plate cushion 1 AA PDUC B074MRPO AH sensor duct 1 AF PCUSUBO042MRPO Air flow cushion 2 AA PCUSGB028MRPO cavity cushion dh AA RBR BIR E RE E E El de E E ER
7. nm ug S G 3 E FUNTKB151MREO JBTN BO065MRFO JBTN B068MRFO MSPRTA050WREO Button Spring PSHEPB023MRE0 LED sheet 3 8 XEPSD30P10XSO Screw Control unit mtg Key unit R 420BW Open Button R 420BK Open Button R 420BW S Gm gt o ME 42 R 420BK R 420BW RefNo PartNo 5 Description oy Code CDORFB213MRKO CDORFB214MRKO FCOV B101MRK0A FCOV B103MRK0A FDORFB062MRTO assembly R 420BK assembly R 420BW screen assembly R 420BK screen assembly R 420BW panel D m PSHEPBO21MREO Sealer film GCOVHBO03 4MRF0 LSTPPBO21MRFO Latch head MSPRTAO0OA6WREO Latch spring 4 HPNL B077MREO M Door Screen R 420BK HPNL B078MREO Door Screen R 420BW Miscellaneous TCAUABO15MRRO Monitor caution label TCAUABO27MRRO DHHS caution label TCAUABO33MRRO UL SCREW label TINSEB179MRRO Operation manual Choke cover SG S amp S SIS E 5 RE P XN D Q Li LX BZA041WREO Screw Base plate mtg LX CZ0052WREO Screw Latch hook mtg amp AH sensor duct mtg XHTSDAOP12RVO Screw Power cord mtg LX BZ0081YBEO Screw H V Capacitor mtg amp Magnetron mtg XOTSD40P12000 Screw Power transformer mtg Chassis support amp Base plate XCPSD30P08000 Screw T T Motor mtg amp AH sensor mtg XCBSD30P08000 Screw Temperature fuse mtg XHTSD40P08000 Screw Magnetron duct mtg LX CZA038WREO Screw O C Cabinet
8. 4 A continuity check across either of the temperature fuse terminals should indicate a closed circuit unless the temperature of the magnetron temperature fuse reaches 144 C or the oven cavity fuse reaches 144 C An open magnetron temperature fuse indicates overheating of the magnetron as sembly while an open oven fuse indicates overheating of the oven cavity If a temperature fuse indicates an open circuit exchange that temperature fuse and check for a restricted air duct re stricted air flow to the magnetron and oven cavity through the vent holes of the oven cavity espe cially the air duct and cooling fan assembly 5 Reconnect all leads removed from components during testing 6 Re install the outercase cabinet 7 Reconnect the power supply cord after installing the outer case cabinet 8 Run the oven and check all functions G Touch Control Panel Assembly Test The touch control panel consists of circuits including semiconductors such as LSI ICs etc There fore unlike conventional microwave ovens proper maintenance can not be performed with only a voltmeter and ohmmeter In this service manual the touch control panel assembly is divided into two control units Control Unit and Key Unit Troubleshooting by unit replacement is described according to the symptoms indicated Before testing 1 Disconnect the power supply cord and then remove outer case cabinet 2 Open the door and block it open 3 Discharge the high voltage
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10. 11 SEQ 25 47 EE S14 23 SEG 10 62 22 10 SEG 24 48 13 22 SEG 9 69 225255220 523 9 SEG 23 49 12 21 SEG 8 64 S24 8 SEG 22 50 11 20 SEG 7165 S25 7 SEG ZI saa S10 19 SEG 6 66 526 6 SEG 19 53 S9 18 SEG 5107 55 54 5 SEG 18 54 S8 17 SEQ 3 69 zx ie x RES S3 4 SEG 17155 oni bebes 57 16 SEG wcesue esa pos S2 3 SEG 16 56 ul ovS S6 15 SEG W 1 2 SEG S5 14 SEG 0 72 EEN SO 1 SEG 14 58 19 13 52 SEG20 53 59 SEGISSEGIS OUT Segment data signal Signal Similar to 52827 SEG12 Terminal not used 61 67 SEGH SEGS OUT Segment data signal Signal Similar to SEG27 SES 69 72 SEG3 SEGO OUT Segment data signal Signal Similar to SEG27 73 74 Connected to GND 7 AVSS IN Connected to VC 7 7 COM3 OUT data signal COM3 Connected to LCD signal C3 Pin 29 COM2 OUT data signal COM2 Connected to LCD signal C3 Pin No 28 COM1 OUT Common data signal CON1 Connected to LCD signal C3 Pin No 27 COM0 OUT data signal COMO Connected to LCD signal C3 Pin No 26 Power source voltage input terminal Standard voltage for LCD 5 6 7 8 9 7 7 24 R 420BK R 420BW SERVICING Precautions for Handling Electronic Components Th
11. 3 The oven is in Compu Defrost condition 4 The oven will operate as follows INDE 47 5 improper operation is indicated the control unit is probably defective and should be checked Key Unit Test Disconnect the power supply cord and then remove outer case cabinet Open the door and block it open Discharge the high voltage capacitor If the display fails to clear when the STOP CLEAR pad is depressed first verify the flat ribbon is making good contact and verify that the door sensing switch operates properly contacts are closed when the door is closed and open when the door is open If the door sensing switch is good disconnect the flat ribbon cable 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 door sensing 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 faulty and must 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 pad is at fault Reconnect all leads removed from components during testing Re install the outer case cabinet Reconnec
12. key touch sound B completion sound P53 OUT Used for Initial balancing of the bridge circuit absolute humidity sensor P52 OUT Oven lamp fan motor and turntable motor driving signal To turn on and off shut off relay RY1 The square waveform voltage is delivered to the RY 1 driving circuit and RY 2 control circuit 16 7 msec During Cooking Rah lt Used for Initial balancing of the bridge circuit absolute humidity sensor Magnetron high voltage circuit driving signal To turn on and off cook relay RY2 In high operation the signals holds H level during micro wave cooking and L level while not cooking In other cooking modes variable cooking the signal turns to H level and L level in repetition according to the power level P51 OUT P50 OUT P47 OUT a ua Aj N CO N OFF 77 7 H GND P 70 24 sec x x 8 sec L 5V Signal coming from touch key When either G 12 line on key matrix is touched a corresponding signal out of P20 P27 will be input into PA6 When no key is touched the signal is held at H level Signal similar to P46 When either G11 line on key matrix is touched a corresponding signal will be inputted into P45 N 45 NO A 22 R 420BK R 420BW Signal similar to P46 P 4 When either G10 line on key matrix is touched a corresponding signal will be inputted into P44 4 4
13. the magnetron temperature fuse remains closed However when abnormally high temperatures are reached within the magnetron the fuse will open at 144 C causing the oven to shut down Note This is a fuse and it does not reset Door Open Mechanism The door is opened by pushing the open button on the control panel When the open button is pushed the open button pushes up the switch lever and then the switch lever pushes up the latch heads The latch heads are moved upward and released from the latch hook Now the door will open Door Sensing Secondary Interlock Switches The secondary interlock switch is mounted in the lower position of the latch hook and the door sensing switch in the primary interlock system is mounted in the upper position of the latch hook They are activated by the latch heads on the door When the door is opened the switches interrupt the circuit to all components except the oven lamp A cook cycle cannot take place until the door is firmly closed thereby activating both interlock switches The primary interlock system consists of the door sensing switch and the primary interlock relay lo cated on the control panel circuit board Monitor Switch The monitor switch is activated the contacts opened by the latch head on the door while the door is closed The switch is intended to render the oven inoperative by means of blowing the monitor fuse when the contacts of the primary interlock relay and seconda
14. are finished 1 Disconnect the power supply cord and then remove outer case cabinet 2 Open the door and block it open 3 Discharge the high voltage capacitor 4 Disconnect the leads to the primary of the power transformer 5 Ensure that the leads remain isolated from other components and oven chassis by using insu lated tape 6 After the above procedure reconnect the power supply cord 7 Follow the troubleshooting guide given below for repair ne Occurrence Cause or Correction The rated AC voltage is not present between Check supply voltage and oven power cord Pin No 1 of the 2 pin connector A and the common terminal of the relay RY1 2 The rated AC voltage is present at primary Low voltage transformer or secondary circuit side of low voltage transformer defective Check and repair 8 Disconnect the power supply cord and then remove the outer case 9 Open the door and block it open 10 Discharge the high voltage capacitor 11 Reconnect all leads removed from components during testing 12 Re install the outer case cabinet 13 Reconnect the power supply cord after the outer case cabinet is installed 14 Run the oven and check all functions 17 R 420BK R 420BW TEST PROCEDURES Procedure Letter Component Test J Compu Defrost Test 1 Place one cup of water in the center of the turntable tray in the oven cavity 2 Close the door touch the Stakes chops pad once
15. capacitor 4 Disconnect the leads to the primary of the power 5 Ensure that these leads remain isolated from other components oven chassis by using insu lated tape 6 After that procedure re connect the power supply cord 14 R 420BK R 420BW TEST PROCEDURES Procedure Letter Component Test G Continued Touch Control Panel Assembly Test 1 Key Unit Disconnect the power supply cord and then remove outer case cabinet Open the door and block it open Discharge the high voltage capacitor Check unit ribbon connection before replacement Reconnect all leads removed from components during testing Re install the outercase cabinet Reconnect the power supply cord after the outer case is installed Run the oven and check all functions 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 If the key unit is defective Disconnect the power supply cord and then remove outercase cabinet Open the door and block it open Discharge the high voltage capacitor Replace the key unit l Reconnect all leads removed from components during testing Re install the outercase cabinet Reconnect the power supply cord after the outer case is installed Run the oven and check all functions 2
16. screw driver 5 Remove the oven lamp socket from the magnetron duct by turning the socket counterclockwise Push ing the small tab of magnetron locating the left hand F side of lamp socket 6 Pull the wire leads from the oven lamp socket by pushing the terminal hole of the oven lamp socket with the small flat type screw driver 7 Remove the oven lamp from the oven lamp socket by turning the oven lamp 8 Now the oven lamp and lamp socket are free Note orange wires must be connected to the terminal with blue mark on the lamp socket Turntable Motor Removal CAUTION Do not drop the turntable motor cover into the oven after cut ting the bridges Because it will damage the wire leads of the motor and it is difficult to remove it out of the oven 1 Disconnect the power supply cord 2 Remove turntable and turntable support from oven cavity 3 Lay the oven on its backside Remove the turntable ROTATE TURNTABLE y d MOTOR COVER gt 2 BASE PLATE Turntable motor cover removal motor cover by snipping off the material in four cor ners 4 When the corners have been snipped off bend the corner areas flat No sharp edges must be evident after removal of the turntable motor cover 5 Disconnect wire leads from turntable motor 6 Remove two 2 screws holding turntable motor to oven cavity 7 Now turntable motor is free SCREW CUTTING PLIER
17. test should indicate an infinite resistance 1f there is little or no resistance the magnetron is grounded shorted and must be replaced Reconnect all leads removed from components during testing Re install the outercase cabinet Reconnect the power supply cord after installing the outer case cabinet Run the oven and check all functions MICROWAVE OUTPUT POWER The following test procedure should be carried out with the microwave oven in a fully assembeled condition outer case fitted HIGH VOLTAGES ARE PRESENT DURING THE COOK CYCLE SO EXTREME CAUTION SHOULD BE OBSERVED Power output of the magnetron can be measured by performing a water temperature rise test This test should only be used if above tests do not indicate a faulty magnetron and there is no defect in the following components or wiring high voltage rectifier high voltage capacitor and power trans former This test will require 16 oz 453cc measuring cup and an accurate mercury thermometer or thermocouple type temperature tester For accurate results the following procedure must be fol lowed 1 Fill the measuring cup with 16 oz 453cc of tap water and measure the temperature of the water with a thermometer or thermocouple temperature tester Stir the thermometer or thermocouple through the water until the temperature stabilizes Record the temperature of the water 2 Placethe cup of water in the oven Operate oven on HIGH selecting 62 seconds cook time Allo
18. which will be found in the Test Procedure section Before replacing a blown monitor fuse test the door sensing switch primary interlock relay sec ondary interlock switch and monitor switch for proper operation Refer to Test Procedure sec tion IMPORTANT Whenever troubleshooting is performed the power supply must be disconnected In some cases it may be neces sary to connect the power supply after the outer case cabinet has been removed In this event Disconnect the power supply cord and then remove outer case cabinet Open the door and block it open Discharge the high voltage capacitor Disconnect the leads to the primary of the power transformer Ensure that the leads remain isolated from other components and oven chassis by using insulated tape After the above procedure install the outer case cabinet reconnect the power supply cord When the testing is completed Disconnect the power supply cord and then remove outer case Open the door and block it open Discharge the high voltage capacitor Reconnect the leads to the primary of the power transformer Re install the outer case cabinet Reconnect the power supply cord after the outer case is installed Run the oven and check all functions Troubleshooting Guide Off Condition Possible Cause Home fuse blows when power cord is Shorted power cord wire harness Check or replace plugged into the wall rec
19. with the pliers b Remove the fan blade from the shaft of the fan mo tor by pulling and rotating the fan blade with your hand c Now the fan blade will be free CAUTION Do not use this removed fan blade again because the hole for shaft may become bigger than a standard one c Install the fan blade to the shaft of the fan motor by pushing the fan blade with a small light weight ball peen hammer or rubber mallet CAUTION Do not hit the fan blade strongly when installed be cause the bracket may be disfigured Make sure that the fan blade rotates smooth after installation Make sure that the axis of the shaft is not slanted 2 Install the fan motor to the back plate of the oven cav ity with two 2 screws 3 Connect the wire leads to the fan motor referring to the wiring diagram Shaft Side View S Shaft a tator ese are the positions Axis L which should be pinched Ile Center of Gap S J with pliers bracket Rotor Bracket 29 R 420BK R 420BW 1 2 3 COMPONENT REPLACEMENT ADJUSTMENT PROCEDURE Door Sensing Switch Secondary Interlock Switch and Monitor Switch Adjustments Disconnect the power supply cord and remove outer case cabinet Open the oven door and block it open Discharge the high voltage capacitor If the door sensing switch secondary interlock switch and monitor switch do not operate properly due to a misadjustment the following adjust
20. 1 inch 3cm to free it from retaining clips on the cavity face pae 6 Lift entire case from the unit When replacing the outer case the 2 spe cial Torx screws must be reinstalled in the same locations Power Transformer Removal 1 Disconnect the power supply cord and remove outer case cabinet 2 Open the oven door and block it open 3 Discharge high voltage capacitor 4 Disconnect wire leads of the main wire harness and H V wire from power transformer 5 Disconnect the lead from magnetron filament 6 Disconnect the leads of the power transformer from high voltage capacitor 7 Remove the four 4 screws holding the transformer to base plate 8 Remove the transformer 9 Now the power transformer is free Re install 1 Resttransformer on baseplate with its pumary termi nals toward oven face plate 2 Secure transformer with four 4 screws to base plate 3 Re connect the wire leads primary and high volt age to transformer and filament leads of transformer to magnetron and high voltage capacitor Refer to Wiring Diagram 4 Re install outercase cabinet and check that oven is operating properly High Voltage Rectifier and High Voltage Capacitor Removal CAUTION When replacing the high voltage rectifier and high volt age capacitor the ground side terminal of the high voltage rectifier must be secured firmly with a ground ing screw 1 Disconnect the power supply cord and remove outer
21. Control Unit The following symptoms indicate a defective control unit Before Replacing the control unit per form the Key unit test Procedure K 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 All the segments of a digit flicker 2 3 Other possible problems 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 When testing is completed Disconnect the power supply cord and then remove outer case cabinet Open the door and block it open Discharge the high voltage capacitor Reconnect all leads removed from components during testing Re install the outercase cabinet Reconnect the power supply cord after installing the outer case cabinet Run the oven and check all functions 15 R 420BK R 420BW TEST PROCEDURES Procedure Letter Component Test H Relay Test 1 Disconnect the power supply cor
22. Control Unit consist of Power Unit and LSI Unit The principal functions of these units and their related signals are explained below Key Unit The key unitis composed of a matrix Signals generated in the LSI are sent to the key unit through P20 P27 When a key pad is touched a signal is completed through the key unit and passed back to the LSI through P43 P46 perform the function that was requested Control Unit The Control unit consists of the following 1 Synchronizing Signal Circuit The Power source synchronizing signal is available in order to compose a basic standard time in the clock circuit It accompanies a very small error be cause it works on commercial frequency 2 ACL Circuit A circuitto generate a signal which resets the LSI to the initial state when power is applied 3 Buzzer Circuit The buzzer is responsive to signals from the LSI to 21 emit Audible sounds key touch sound and comple tion sound Door Sensing Switch A switch to tell the LSI ifthe dooris open or closed e Relay Circuit To drive the magnetron fan motor turntable motor and oven lamp D Indicator Circuit This circuit consists of 25 segmenets and 4 com mon electrodes using a liquid Crystal Display Back Light Circuit A circuit to drive the back light Light emmitting diodes LD1 LD5 It incorporates a very small error because it works on commercial frequency N 00 Power Source Circuit This cir
23. EDURE After adjustment of the door interlock and monitor switches are completed individually or collectively a IN TERLOCK SWITCH TEST and MICROWAVE LEAK AGE TEST must be performed to assure compliance with DHHS CDRH Performance Standards for Micro wave Ovens Interlock Switch Test Make sure that the door sensing switch secondary in terlock switch and monitor switch are operating properly by checking with an ohmmeter Refer to the Test Procedure of the door sensing switch secondary interlock switch and monitor switch Microwave Leakage Test Requirements 1 Microwave leakage limit Power density limit The power density of microwave radiation emitted by a microwave oven shall not exceed 1mW cm at any point 5cm or more from the external surface of the oven measured prior to acquisition by the purchaser and thereafter through the useful life of the oven 5mW cm at any point 5cm or more from the external surface of the oven 2 Safety interlock switches Primary interlock relay and door sensing switch will prevent microwave radiation emissions in excess of the requirement as above mentioned secondary interlock switch shall prevent microwave radiation emission in excess of 5mW cm atany point 5cm or more from the external surface of the oven Preparation For Testing Before beginning the actual measurement of leakage proceed as follows 1 Make sure that the actual instrument is operating nor m
24. ENSOR REPLACEMENT Installation Removal Disconnect power supply cord Open the oven door and block it open Remove screws from the rear of the outercase cabi net Slide the entire case back about 1 inch 8cm to free it from retaining clips on the cavity faceplate 4 Lift the entire outercase cabinet from the oven unit 5 Discharge high voltage capacitor 6 Remove two 2 screws holding the AH sensor Refer to Figures 1 16 amp 2 16 Disconnect the AH sensor harness from connector CN F on control unit AH sensor is now free 33 1 Insert new AH sensor into AH sensor duct Refer to Figures 1 16 amp 2 16 for proper sensor orientation 2 Install two 2 screws to secure AH sensor 3 Route the AH sensor harness above emboss on AH sensor duct Refer to Figures 1 16 amp 2 16 Continue to route AH sensor harness across the oven cavity top plate and through the large opening Refer to Figure 2 16 Connect AH sensor harness to CN F on the control unit Re install the outercase cabinet and check for prop er operation R 420BK R 420BW AH SENSOR ORIENTATION amp HARNESS ROUTING AH Sensor Orientation Up NO 1 Mounting p Screw I O AH Sensor Harness AH Sensor Mounting AH Sensor Duct Screw Figure 1 16 Oven Left Side View AH Sensor Harness Figure 2 16 Oven Top View 34 R 420BK R 420BW MICROWAVE MEASUREMENT PROC
25. R 420BK R 420BW SHARP SERVICE MANUAL 28M104R420BE MICROWAVE OVEN MODELS R 420BK R 420BW In the interest of user safety the oven is to be restored to its original condition and only the parts identical to those specified should be used WARNING TO SERVICE PERSONNEL Microwave ovens contain circuitry capable of producing very high voltage and current Contact with the following parts may result in a severe possibly fatal electrical shock High Voltage Capacitor High Voltage Power Transformer Magnetron R 420BK High Voltage Rectifier Assembly High Voltage Harness etc TABLE OF CONTENTS SECTION PAGE PRECAUTIONS TO BE OBSERVED BEFORE AND DURING SERVICE TO AVOID POSSIBLE EXPOSURE TO EXCESSIVE MICROWAVE ENERGY Inside Front Cover Before Servicing Inside Front Cover Warning to Service Personnel Foreword and Warning Specifications General Information Key Unit Layout Operation Servicing and Troubleshooting Guide Test Procedures Touch Control Outline Component Replacement and Adjustment Procedure Microwave Measurement Procedure Wiring Schematic Diagram Parts SHARP ELECTRONICS CORPORATION Service Headquarters Sharp Plaza Mahwah New Jersey 07430 2135 R 420BK R 420BW PRECAUTIONS TO BE OBSERVED BEFORE AND DURING SERVICING TO AVOID POSSIBLE EXPO SURE TO EXCESSIVE MICROWAVE ENERGY a Do not operate or allow the oven to be operated with the door open b Make the following safet
26. REHEAT pad once B The control panel is in the sensor cooking operation C After approximately 20 seconds push plunger of select switch for more than 3 seconds This condition is the same as judgment by AH sensor D After approximately 3 seconds the display shows XX XX which is the remaining cooking time and the display counts down If the above is not the case the control unit is probably defective If the above checks positive the AH sensor is probably defective 10 Disconnect the power supply cord and then remove outer case cabinet 11 Open the door and block it open 12 Discharge the high voltage capacitor 13 Disconnect the dummy resistor circuit from the sensor connector of control panel 14 Carry out the necessary repair 15 Reconnect all leads removed from components during testing and repairing 16 Re install the outer case cabinet 17 Reconnectthe power supply cord after the outer case is installed Run the oven and check all func tions 18 Carry out the Water load cooking test again and ensure that the oven works properly PLUNGER TO CONNECTOR F NC ON CONTROL UNIT NO CONNECTOR COM 2 224 1 1 2W R3 4 3kQ 59 1 4W R4 1 5 1 4W Figure A Sensor Dummy Resistor Circuit 20 R 420BK R 420BW OUTLINE OF TOUCH CONTROL PANEL The touch control section consists of the following units as shown in the touch control panel circuit 1 Key Unit 2 Control Unit The
27. Remove the AH sensor Install the new AH sensor Reconnect all leads removed from components during testing Re install the outer case Reconnect the power supply cord and check the sensor cook operation proceed as follows A Fill approximately 200 milliliters 7 2 oz of tap water in a 1000 milliliter measuring cup B Place the container on the center of tray in the oven cavity C Close the door D Touch SENSOR REHEAT pad E The control panel is in automatic Sensor operation F The oven will turn off automatically when the water is boiling bubbling If the new sensor does not operate properly the problem is with the control unit Checking the Control Unit 1 Disconnect the power supply cord and then remove outer case cabinet 2 Open the door and block it open 3 Discharge the high voltage capacitor 4 Disconnect the sensor connector that is mounted to control panel 5 Then connect the dummy resistor circuit see fig A to the sensor connector of control panel OO O Q N 9 R 420BK R 420BW TEST PROCEDURES Procedure Letter Component Test L Checking the Control Unit Continued 6 Disconnect the wire leads to the primary of power transformer 7 Ensure that these leads remain isolated from other components and oven chassis by using insu lated tape 8 After that procedure re connect the power supply cord 9 Check the sensor cook operation proceed as follows A Touch SENSOR
28. TURNTABLE MOTOR COVER Turntable motor cover re install R 420BK R 420BW COMPONENT REPLACEMENT ADJUSTMENT PROCEDURE Turntable Motor Re install 1 Remove any sharp edges on the turntable motor cover and the base plate with cutting pliers 2 Insert the edge of motor cover into tab on the base plate 3 Secure motor cover with one 1 screw to base plate Cooling Fan Motor Removal 1 Disconnectthe power supply cord and remove outer case cabinet INSTALLATION 1 Install the fan blade to the fan motor shaft according 2 Open the oven door and block it open to the following procedure 3 Discharge the high voltage capacitor a Hold the center of the bracket which supports the 4 Disconnect the wire leads from the fan motor shaft of the fan motor on the flat table 5 Remove two 2 screws holding the fan motor to the b Apply the screw lock tight into the hole for shaft of back plate of the oven cavity the fan blade 6 Remove the fan blade from the fan motor shaft ac I cording to the following procedure a Hold the edge of the rotor of the fan motor by using a pair of groove joint pliers CAUTION Make sure that any pieces do not enter the gap be tween the rotor and the stator of the fan motor because the rotor is easily shaven by pliers and metal pieces may be produced Do not touch the pliers to the coil of the fan motor because the coil may be cut or injured Do not disfigure the bracket by touching
29. Test To protect the electronic circuits this model is provided with a fine foil pattern added to the primary on the PWB which acts as a fuse 1 Foil Pattern check and repairs 1 Disconnect the power supply cord and then remove outer case cabinet 2 Open the door and block it open 3 Discharge the high voltage capacitor 4 Follow the troubleshooting guide given below for repair Steps Occurrence CaueorComection Only pattern at a is broken Insert jumper wire J1 and solder Pattern at a and b are broken Insert the coil RCILE2003YAZZ between and 16 R 420BK R 420BW TEST PROCEDURES Procedure Letter Component Test l Continued Procedures to betaken when the foil pattern of the EE wiring board PWB is open Oo 5 Make a visual inspection of the varistor burn damage and test the transformer with an ohm meter for the presence of layer short circuit check the primary coil resistance which is approximately 227 Q 15 If any abnormal condition is detected replace the defective part s 0 D N 4 o lt JJ m O 6 Reconnect all leads removed from components during testing 7 Re install the outercase cabinet 8 Reconnect the power supply cord after installing the outer case cabinet 9 Run the oven and check all functions 2 Follow the troubleshooting guide given below If indicator does not light up after above check and repairs
30. The following is a description of component functions during oven operation Off Condition Closing the door activates the door sensing switch and secondary interlock switch In this condition the moni tor switch contacts are opened When the oven is plugged in 120 volts AC is supplied to the control unit see schematic diagram The display flashes 88 88 To set any program or set the clock first touch the STOP CLEAR pad The display clears and appears and the control unit counts every minute Cooking Condition Program desired cooking time and Variable Cooking Control by touching the NUMBER pads and the Power Level pad of the Variable Cooking Control When START is touched the following operations occur 1 The relay contacts are closed and components con nected to the relays RY 1 and RY 2 are turned on For details see table below Oven Lamp Turntable Motor Fan Motor 2 120 volts is supplied to the primary winding of the power transformer and is converted to approximate ly 3 4 volts AC on the filament winding and approxi mately 2400 volts AC on the high voltage winding 3 The filament winding voltage heats the magnetron filament and the high voltage is sent to a voltage dou bler circuit 4 The microwave energy produced by the magnetron is channeled through the waveguide into the cavity feed box and into the cavity where the food is cooked 5 Upon completion of the cooking cycle the power
31. ally as specified in its instruction booklet Note Survey instruments that comply with the require ment for instrumentation 21CFR1030 10 c 3 i as prescribed by the performance standard for microwave ovens must be used for testing 35 2 Place the oven tray in the oven cavity 3 Place the load of 275 15ml 9 8 oz of tap water ini tially at 20 5 C 68 F in the center of the oven cav ity The water container shall be a low form of 600 ml 20 oz beaker with an inside diameter of approximately 8 5 cm 3 in and made of an electrically noncon ductive material such as glass or plastic The placing of this standard load in the oven is impor tant not only to protect the oven but also to insure that any leakage is measured accurately 4 Set the cooking control on High 5 Close the door and put the oven into a cook cycle for several minutes If the water begins to boil before the survey is completed replace it with 275ml of cool wa ter Leakage Test Closed door leakage test microwave measurement 1 Grasp the probe of the survey instrument and hold it perpendicular to the gap between the door and the body of the oven 2 Move the probe slowly not faster than 1in sec 2 5cm sec along the gap watching for the maxi mum indication of the meter 3 Check for leakage at the door screen sheet metal seams and other accessible positions where the con tinuity of the metal has been breached eg around
32. ault 3 Discharge the high voltage capacitor and wait for Fan blade Fan motor Switch Switch lever and 60 seconds Open button 3 Do not catch the wire leads in the outer case cabi 2 Don t let the wire leads touch the following parts net 1 High voltage parts 4 Insert the positive lock connector until its pin is Magnetron High voltage Transformer High volt locked and make sure that the wire leads do not age capacitor and High voltage rectifier assembly come off even if the wire leads are pulled 2 Hot parts 5 To prevent an error function connect the wire leads Oven lamp Magnetron High voltage Transform correctly referring to the Wiring Diagram 26 R 420BK R 420BW COMPONENT REPLACEMENT ADJUSTMENT PROCEDURE NOTE Please refer to OVEN PARTS CABINET PARTS CONTROL PANEL PARTS DOOR PARTS When carrying out any of the following removal procedures Outer Case Removal CAUTION 1 Disconnect power supply cord before removing outer case cabinet 2 Discharge the high voltage capacitor before touching any oven components or wiring To remove the outer case proceed as follows 1 Disconnect the power supply cord 2 Open the oven door and block it open 3 Remove the two screws 2 from the upper and lower left portion of rear cabinet using a T20H Torx type or GTXH20 100 screw driver 4 Remove the two screws 2 from the rear of outer case 5 Slide the entire case back about
33. button and open the door slightly 3 Insert a putty knife thickness of about 0 5mm into the gap between the choke cover and corner portion of door panel as shown in the figure below to free en gaging parts 4 Pry the lever and lift up the choke cover by inserting a putty knife in the order as shown in the figure below 5 Release choke cover from door panel 6 Now choke cover is free from door panel OP gt 1 S 8 2 Choke Cover 7 Release two 2 pins of door panel from two 2 hole of upper and lower door hinges by lifting up 8 Now door panel is free from oven cavity 9 Release door panel from eight 8 tabs of door frame and remove door frame 10 Now door panel with sealer film is free 11 Tear sealer film from door panel 12 Now door panel is free 13 Slide latch head upward and remove it from door frame and latch head 14 Now latch head and latch spring are free 15 Remove door screen from door frame 16 Now door screen is free Re Install 1 Re install door screen to door frame 2 Re install latch spring to the head Re install latch spring to the door frame 3 Re install door panel to door frame by fitting eight 8 tabs of door frame to eight 8 holes of door panel 4 Put sealer film on door panel Refer to Sealer Film Installation and on how to handle the new film 5 Catch two 2 pins of door panel on two 2 holes of upper and lower door hinge 6 Re insta
34. case cabinet Open the oven door and block it open Discharge high voltage capacitor Remove one 1 screw holding the capacitor band and the high voltage rectifier assembly to the base plate 5 Disconnect the wire lead of high voltage rectifier as sembly from the magnetron 6 Disconnect terminals of rectifier assembly from ca pacitor and magnetron High voltage rectifier assem bly is now free RDA1504U CAUTION Do not replace only high voltage rectifier When re placing it replace the entire high voltage rectifier as sembly Magnetron Removal Disconnect the power supply cord and remove outer case cabinet Open the oven door and block it open Discharge high voltage capacitor Disconnect wire leads from the magnetron Remove the one 1 screw holding chassis support to magnetron and magnetron duct Slide the magne tron duct slightly so that two 2 screws at left hand C spa IS 21 side of the magnetron appear 6 Carefully remove the four 4 screws holding magne tron to waveguide flange 7 Remove the magnetron with care so that the magne tron antenna is not hit by any metal objects around the tube 8 Now the magnetron is free R 420BK R 420BW COMPONENT REPLACEMENT ADJUSTMENT PROCEDURE Magnetron Installation 1 Installmagnetron assembly to the waveguide flange with care to prevent damage to the magnetron tube 2 Secure the magnetron with four 4 screws
35. cuit generates voltage necessary in the con trol unit from the AC line voltage In addition the synchronizing signal is available in orderto compose a basic standard time in the clock circuit Symbol Application LSI IC1 9 Absolute Humidity Sensor Circuit This circuit detects the humidity of the food which is being cooked to control automatic cooking R 420BK R 420BW DESCRIPTION OF LSI The I O signals of the LSI IZA865DR is detailed in the following table Power source voltage input terminal Standard voltage for LCD Terminal to change functions according to the Model By using the A D converter contained in the LSI DC voltage in accordance with the Model in operation is applied to set up its cooking constant AN3 OUT Terminal not used AN2 1 2 VL2 VL1 3 6 AN7 AN4 To Input signal which communicates the door open close information to the LSI Door closed H level signal 0V Door opened L level signal 5V AN1 AH Sensor input This is an analog input terminal from the AH sensor circuit and is connected to the A D converter built in to the LSI Used for Initial balancing of the bridge circuit absolute humidity sensor This input is analog input terminal from the AH sensor circuit and connected to the A D converter built into the LSI Terminal not used 11 13 P57 P55 OUT P54 OUT Signal to sound Buzzer 2 0 kHz 0 1 sec Le A
36. d and then remove outer case cabinet 2 Open the door and block it open 3 Discharge the high voltage capacitor 4 Disconnect the leads to the primary of the power transformer 5 Ensure that the leads remain isolated from other components and oven chassis by using insulated tape After the above procedure reconnect the power supply cord 7 Check voltage between Pin No 1 of the 2 pin connector A and the common terminal of the relay RY2 on the control unit with A C voltmeter The meter should indicate 120volts If not check oven circuit RY 1 and RY 2 Relay Test These relays are operated by D C voltage Check voltage at the relay coil with a D C voltmeter during the microwave cooking 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 O gt Relay Symbol Operational Voltage Connected Components Approx 24 0 V DC Oven lamp Turntable motor Cooling fan motor RY2 Approx 23 0 V DC 8 Disconnect power supply cord 9 Open the door and block it open 10 Discharge the high voltage capacitor 11 Reconnect all leads removed from components during testing 12 Re install the outer case cabinet 13 Reconnect the power supply cord after installing the outer case cabinet 14 Run the oven and check all functions Foil pattern on the printed wiring board
37. during testing Re install the outercase cabinet Reconnect the power supply cord after the outer case is installed Run the oven and check all functions Primary Interlock System Test Door Sensing Switch Disconnect the power supply cord and then remove outercase Open the door and block it open Discharge the high voltage capacitor Isolate the switch and connect the ohmmeterto the common COM and normally open NO termi nal of the switch The meter should indicate an open circuit with the door open and a closed circuit with the door closed If improper operation is indicated replace the door sensing switch Reconnect all leads removed from components during testing Re install the outercase cabinet Reconnect the power supply cord after the outer case is installed Run the oven and check all functions 03 ONO CO CON 12 R 420BK R 420BW TEST PROCEDURES Procedure Letter Component Test E Continued Primary Interlock Relay RY 2 Disconnect the power supply cord and then remove outer case cabinet Open the door and block it open Discharge the high voltage capacitor Disconnect two 2 wire leads from the relay on the printed circuit board in the control panel assem bly The relay is located on the bottom portion of the circuit board on the backside of the control panel assembly Connect an ohmmeter to the male terminals and observe the m
38. e at the AN1 terminal of the LSI Then the LSI observes that voltage at AN1 terminal and compares it with its initial value When the comparison rate reaches the preset value fixed for each menu to be cooked the LSI caused the unit to stop sensor cooking thereafter the unit goes into the next operation automatically When the LSI starts to detect the initial voltage at AN1 terminal 16 seconds after the unit has been put in the Sensor Cooking mode if it is impossible to take a bal ance of the bridge circuit due to disconnection of the ab solute humidity sensor ERROR will reappear on the dis play and cooking is stopped Absolute Humidity Sensor Circuit S Thermistor open vessel Va 15V Va 15V VC 5V Thermistor closed vessel R 420BK R 420BW AH SENSOR DUCT REMOVAL 1 Disconnect the power supply cord 7 Slide the two tabs of the sensor duct to the right 2 Open the oven door and block it open 8 Sensor duct is now free 3 Remove screws from the rear of the outercase cabi net Slide the entire case back about 1 inch 3cm to free it from retaining clips on the cavity faceplate CAUTION 4 Discharge the high voltage capacitor Discharge the high voltage capacitor before touching any oven components or wiring 5 Lift entire outer case cabinet from unit 6 Remove ground screw mounted into the sensor duct Sensor Ground screw Slide Slide Sensor Duct LP AH S
39. e capacitor before touching any oven components or wiring Disconnect the power supply cord and then remove outercase Open the door and block it open Discharge the high voltage capacitor If the capacitor is open no high voltage will be available to the magnetron Disconnect input leads and check for short or open between the terminal using an ohmmeter Checking with a high ohm scale if the high voltage capacitor is normal the meter will indicate conti nuity initially and once the capacitor is charged an open circuit If the above is not the case check the capacitor with an ohmmeter to see if it is shorted between each terminal and case If it is shorted replace the capacitor Reconnect all leads removed from components during testing Re install the outercase cabinet Reconnect the power supply cord after the outer case is installed Run the oven and check all functions 03 COON C1 E Secondary Interlock Switch Test Disconnect the power supply cord and then remove outercase Open the door and block it open Discharge the high voltage capacitor Isolate the switch and connect the ohmmeterto the common COM and normally open NO termi nal of the switch The meter should indicate an open circuit with the door open and a closed circuit with the door closed If improper operation is indicated replace the secondary interlock switch Reconnect all leads removed from components
40. e personnel should inform SHARP ELECTRONICS CORPORATION of any certified unit found with emissions in excess of 4mW cm The owner of the unit should be instructed not to use the unit until the oven has been brought into compliance RD81001U R 420BK R 420BW SERVICE MANUAL SHARP Microwave Ovens Specifications R 420BK R 420BW Foreword General Information This manual has been prepared to provide Sharp Electronics Corporation personnel with complete operation and service information for Sharp microwave oven models R 420BK R 420BW It is recommended that service personnel carefully study the entire text of this manual so they will be qualified to render satisfactory customer service Check interlock switches and the door seal carefully Special attention must be given to avoid electrical shock and microwave radiation hazards WARNING Never operate the oven until the following points are en sured A The door is tightly closed B The door brackets and hinges are not defective C The door packing is not damaged D The door is not deformed or warped Touch Control Panel E There are no other visible signs of damage to the oven DANGER Certain initial parts are intentionally not grounded and present a risk of electrical shock only during servicing Service personnel Do not contact the fol lowing parts while the appliance is energized High Voltage Capacitor Power Transformer Magne tron High Volta
41. ed it should be a 3 wire 15 ampere minimum cord CAUTION Do not under any circumstances cut or remove the round grounding prong from this plug Oven Diagram Digital display Auto Touch control panel Door open button Door latches Removable turntable support Removable turntable Oven lamp Oven door with see through window Waveguide cover 0 Power Cord Key Unit Layout Indicators b Lighted digital display c SENSOR COOK pad Touch to cook popular items using a pre set time constant Instant Action pad INSTANT ACTION pad Pre set time constant for some popular food items in ev eryday life style COMPU DEFROST pad Touch to defrost certain foods Number selection pads AUTO START CLOCK pad Touch to set clock or auto start time KITCHEN TIMER pad Touch to set minute function i START pad Touch to start oven MINUTE PLUS pad Touch to cookfor 1 minute at 10096 power orto increase cooking time STOP CLEAR pad Touch to erase during programming Touch once to stop operation of oven during cooking Touch twice to cancel cooking program POWER LEVEL pad Touch to select microwave power setting wl wir wl WM Alo IN AL TAL IN N COOK SENSOR LB KG DEF HELP SENSOR COOK MINUTE PLUS KITCHEN auto START R 420BK R 420BW R 420BK R 420BW OPERATION Description of Operating Sequence
42. en Procedure A load incompletely cooked or not cooked at allt the end of Power transformer Procedure B Low voltage Check Dirty oven cavity Check Wrong operation Check Shorted or open wiring Check or replace Oven goes into a cook cycle but ex tremely uneven heating is produced in oven load food Oven does not cook properly when programmed for Cooking Power P 50 MED mode Operates properly on Cooking Power P HI HIGH mode Oven goes into COMPU DEFROST but food is not defrosted well Control unit Procedure G Wrong operation Check Dirty oven check Compu Defrost Procedure J The oven is the sensor cooking condition but AH sensor does not end or AH sensor turns off about a maxi mum of 30 minutes after start When a cup of water is heated by sensor the oven does not shut off when the water is boiling 10 R 420BK R 420BW TEST PROCEDURES Procedure Letter Component Test A Magnetron Assembly Test Disconnect the power supply cord and then remove outercase cabinet Open the door and block it open Discharge the high voltage capacitor To test for an open filament isolate the magnetron from the high voltage circuit A continuity check across the magnetron filament leads should indicate less than 1Q To test for a shorted magnetron connect the ohmmeter leads between the magnetron filament leads and chassis ground This
43. eptacle Monitor fuse blows when poweris ap Shorted power cord or wire harness Check or replace plied Secondary interlock or monitor Procedure E Switch Monitor switch or monitor fuse Contre ui Primary interlock relay or door sens ing switch Control unit Procedure G Shorted or open wiring Monor fuse Oven temperature fuse Procedure F Control uni Relay Display does not illuminate when power cord is plugged in Display does not operate properly when STOP CLEAR button is touched Oven lamp does not light with door opened R 420BK R 420BW Troubleshooting Guide Cook Condition Possible Cause Shorted or open wiring Oven lamp or socket Test Procedure Check or replace Check or replace Procedure G Check or replace Check or replace Check or replace Check or replace Procedure E Procedure E Procedure F Problem 5 D G o s 3 Oven lamp does not light at all Oven lamp lights but fan motor and turntable motor do not operate Shorted or open wiring Cooling fan motor Oven does not go into cook cycle when START button is touched Shorted or open wiring Primary interlock system Monitor fuse Magnetron or oven temperature fuse Relay Oven seems to be operating but Shorted or open wiring Check or replace little or no heat is produced in ov
44. eter reading The relay contacts should be open Ifthe relay contacts are closed replace the primary interlock relay or the circuit board Reconnect all leads removed from components during testing Re install the outer case cabinet Reconnect the power supply cord after installing the outer case cabinet Run the oven and check all functions Monitor Switch Test Q COON O O1 Disconnect the power supply cord and then remove outer case cabinet Open the door and block it open Discharge the high voltage capacitor Disconnect the oven from the power supply Before performing this test make sure that the secondary interlock switch and primary interlock relay are operating properly referring to the above Switch Test Procedure Disconnect the wire lead from the monitor switch NC terminal Check the monitor switch operation by using the ohmmeter as follows When the door is open the meter should indicate a closed circuit With the door open take a screw driver and push in the monitor switch actuator located through the lower latch hole on the faceplate of the cavity The meter should indicate a open circuit If improper operation is indicated the monitor switch may be defective and should be replaced After testing the monitor switch re connect the wire lead to the monitor switch NC terminal and check continuity of the monitor circuit Reconnect all leads removed from components during testing Re instal
45. ge Rectifier Assembly and High volt Microwave Measurement age Harness If provided Vent Hood Fan Assembly and Cooling Fan motor Troubleshooting Test Procedures All of the parts marked 7 on parts list are used at volt ages more than 250V Wiring Schematic Diagram Removal of the outer case cabinet gives access to volt age above 250V All of the parts marked A on parts list may cause undue microwave exposure by themselves or when they are damaged loosened or removed Sharp Electronics Corporation Sharp Plaza Mahwah New Jersey 07430 2135 R 420BK R 420BW WARNING TO SERVICE PERSONNEL Microwave ovens contain circuitry capable of producing very high voltage and current Con tact with following parts may result in a severe possibly fatal electrical shock EXAMPLE High Voltage Capacitor High Voltage Power Transformer Magnetron High Voltage Rectifier Assembly High Voltage Harness etc Read the Service Manual carefully and follow all instructions Before Servicing 1 Disconnect the power supply cord and then remove outer case 2 Open the door and block it open 3 Discharge the high voltage capacitor WARNING RISK OF ELECTRICAL SHOCK DISCHARGE THE HIGH VOLTAGE CAPACITOR BEFORE SERVICING The high voltage capacitor remains charged about 60 se conds after the oven has been switched off Wait for 60 se conds and then short circuit the connection of the high volt age capacitor
46. grnd 6 10 XHTSD40P08RVO Screw Fan motor mtg 6 11 LX CZBO11MREO M Screw UL O C Cabinet 43 pov ico 2 LJ A d 4 5 d 72 7 d 44 k Cavity Assembly R 420BK R 420BW Control Panel Assembly Door Assembly p 45 R 420BK R 420BW EE E EE EE Wire Harnesses Packing and Accessories PACKING KIT DOOR PROTECTION SHEET 22 TRAY HOLDER x f e TRAY e pp Q AMT N A 2 7 d P H N d Q ei d 1 D NUS 00 lt Actual harnesses may be different than illustrations C PLASTIC BAG TRAY PACK BE E 5 Sasi Jasa ue EE PACKING CASE Non replaceable items PRSE ONES Geer ee EE GNE 98 SHARP CORP 3M5 05E Printed in U S A 46
47. ions Microwave ovens should not be operated empty Totest for the presence of microwave energy within a cavity place a cup of cold water on the oven turntable close the door and set the power to HIGH and set the microwave timer for two 2 minutes When the two minutes has elapsed timer at zero carefully check to see if the wa ter is hot If the water remains cold carry out Before Servicing procedure and re examine the connection to the component being tested When all service work is completed and the oven is fully assembled the microwave power output should be checked and the microwave leakage test should be car ried out R 420BK R 420BW SPECIFICATIONS Wem Desen Power Requirements 120 Volts 14 Amperes 1650 Watts 60 Hertz Single phase 3 wire grounded Power Output 1100 watts IEC 705 Test Procedure Operating frequency of 2450 MHz Case Dimensions Width 211146 Height 123 including feet Depth 173 5 Width 15 Height 817 23 Depth 163 4 Tray Size 141 Diameter Cooking Cavity 1 3 Cu Ft Control Complement Touch Control System Clock 1 00 12 59 Timer 0 99 min 99 sec Microwave Power for variable cooking Repetition Rate P HI HIGH Full power throughout the cooking time 2 27 approx 90 of full power P60 cee d approx 80 of full power P 70 MED HIGH approx 70
48. is unit uses CMOS LSI in the integral part of the cir cuits When handling these parts the following precau tions should be strictly followed CMOS LSI have extremely high impedance at its input and output terminals For this reason it is easily in fluenced by surrounding high voltage power sources static electricity charge in clothes etc and sometimes it is not fully protected by the built in protection circuit In order to protect CMOS LSI practice the following guidelines 1 When storing and transporting LSI thoroughly wrap them in aluminum foil Also wrap all PW boards in aluminum foil 2 When soldering the technician should use a ground ing strap as shown in the figure and use a grounded soldering iron and work table Approx 1MQ Shapes of Electronic Components Transistor C B KRC243M E Transistor B 2SB1238 E C Servicing of Touch Control Panel We describe the procedures to permit servicing of the touch control panel of the microwave oven and the pre cautions you must take when doing so To perform the servicing powerto the touch control pan elis available either from the power line of the oven itself or from an external power source Servicing The Touch Control Panel With The Oven Power Supply CAUTION The high voltage transformer of the microwave oven is still live during servicing and presents a hazard When checking the performance of the touch control panel put the outer cabinet
49. l the outer case cabinet Reconnect the power supply cord after installing the outer case cabinet Run the oven and check all functions G IN CON Red Wire Connected to Normally Closed Terminal f P WhiteWires Connected to 721 Common Terminal Note1 Connect ohmmeter probes here Note2 Use screwdriver to engage monitor switch actuator Monitor Switch 13 R 420BK R 420BW Procedure Letter Component Test E Continued Open Monitor Fuse 1 Disconnect the power supply cord and then remove outer case cabinet 2 Open the door and block it open 3 Discharge the high voltage capacitor 4 Ifthe monitor fuse is open perform the tests for the primary interlock system secondary interlock switch and the monitor switch according to the procedure outlined in this section Adjust or replace the secondary interlock and door sensing switches When replacing a monitor fuse make sure that the monitor switch is also CAUTION replaced at that time Replace monitor fuse and monitor switch with Part FFS BA016 KIT 5 Reconnect all leads removed from components during testing 6 Re install the outer case cabinet 7 Reconnect the power supply cord after installing the outer case cabinet 8 Run the oven and check all functions F Temperature Fuses 1 Disconnect the power supply cord and then remove outer case cabinet 2 Open the door and block it open 3 Discharge the high voltage capacitor
50. ll choke cover to door panel by snapping on to the door panel Note After any service to the door A Make sure that door sensing switch secondary Interlock switch primary Interlock relay and monitor switch are operating properly Refer to section Test Procedures B An approved microwave survey meter should be used to assure compliance with proper microwave radiation emission limitation standards 31 After adjustment make sure of the following 1 Door latch heads smoothly catch latch hook through latch holes and also latch head goes through the cen ter of the hole 2 Deviation of door alignment from horizontal line of cavity face plate is less than 1 0 mm 3 Door is positioned with its face depressed toward cav ity face plate 4 Install the outer case cabinet and check for micro wave leakage around the door with an approved mi crowave Survey meter Refer to Microwave Measurement Note The door on a microwave oven is designed to act as an electronic seal preventing the leakage of mi crowave energy from the oven cavity during the cook ing cycle This function does not require that the door be air tight moisture tight or light tight Therefore the occasional appearance of moisture light or sensing of gentle warm air movement around the oven door is not abnormal and does not indicate leakage of mi crowave energy from the cavity UPPER DOOR HINGE Sealer Film Installation 1 Pu
51. ment should be made Loosen the two 2 screws holding the latch hook to the oven cavity front flange With the door closed adjust the latch hook by moving it back and forth and up and down In and out play of the door allowed by the upper and lower position of the latch heads should be less than 0 5mm The vertical position of the latch hook should be placed where the door sensing switch and the sec ondary interlock switch have activated with the door closed Secure the screws with washers firmly Make sure of the door sensing switch operation If the door sensing switch has not activated with the door closed loosen the screw and adjust the latch hook position Check operation of all switches If each switch has not activated with the door closed loosen screw and adjust the latch hook position Note After adjustments make sure of the following 1 In and out play of the door remains less than 0 5mm when in the latched position Check the upper position of the latch hook by push ing and pulling the upper portion of the door Door Sensing Switch Monitor Switch 30 Then check lower portion of the latch hook by pushing and pulling the lower portion of the door toward the oven face Both results play of the door should be less than 0 5mm The door sensing and secondary interlock switches interrupt the circuit before the door can be opened Monitor switch contacts close when door is ope
52. mined by ex periment with each food category and is inputted into the LSI The following is an example of how the AH Sensor Works 1 Potatoes at room temperature Vapor is emitted very slowly 2 Heated potatoes Moisture and humidity is emitted rapidly You can smell the aroma as it cooks Mino E I N 3 Sensor detects moisture and humidity and calcu lates cooking time and variable power level Cooking Sequence 1 Touch SENSOR REHEAT pad Note The oven should not be operated in either mode immediately after plugging in the unit Wait five minutes before cooking in sensor mode 2 The coil to the shut off relay RY 1 is energized the oven lamp turntable motor and cooling fan motor are turned on and the power transformer remains off 3 After about 16 seconds the cook relay RY 2 is en ergized The power transformer is turned on micro wave energy is produced and first stage cooking is started Note The 16 second delay is for cooling time required to remove any vapor from the oven cavity and sensor During this first stage do not open the oven door or touch the STOP CLEAR pad 4 When the sensor detects the vapor emitted from the food the display switches over the remaining cook ing time and the timer counts down to zero At this time the door may be opened to stir food turn it or season etc 5 When the timer reaches zero an audible signal sounds The shut off relay and cook relay a
53. ned Re install outer case and check for microwave leak age around the door with an approved microwave survey meter Refer to Microwave Measurement Procedure Door Sensing Switch Secondary Interlock Switch and Monitor Switch Removal 1 2 9 Disconnect the power supply con and remove outer case cabinet The door sensing and secondary interlock switches interrupt the circuit before the door can be opened Discharge high voltage capacitor Disconnect wire leads from switches fuse and c con nectors from control panel Remove one 1 screw holding control panel to oven cavity faceplate Slide control panel assembly upward and remove from cavity faceplate Open oven door 8 Remove two 2 screws holding the latch hook to oven flange Remove latch hook from oven flange by lifting up on flexible tab and pushing latch hook back 10 Locate the flexible retaining tabs on the latch hook 11 Push tab inward and rotate switch counterclockwise to release switch Note For monitor switch lift switch over boss while ro tating counterclockwise 12 Switch is now free reni Tab ee lt Bening Ig switch push inward flexible retaining tab and rotate switch counterclockwise Caution Apply only slight pres sure to retaining tabs to avoid breakage R 420BK R 420BW DOOR DISASSEMBLY Removal 1 Disconnect the power supply cord 2 Push the open
54. of full power SE approx 60 of full power 50 MED approx 50 of full power PAO PRECEPIT approx 4096 of full power P 30 MED LOW approx 30 of full power e ote oaa s asad approx 20 of full power d Lo W approx 1096 of full power MET NEP PET T No power throughout the cooking time FEATURES Instant Action Compu Defrost Sensor Cook Minute Plus Kitchen Timer Variable Power 10 4 Stage Cooking Oven Cavity Light Yes Safety Standard UL Listed FCC Authorized DHHS Rules CFR Title 21 Chapter 1 Subchapter J R 420BK R 420BW GENERAL INFORMATION Grounding Instructions Grounded This oven must be fully grounded at all times This GE Receptacle Box appliance must be connected to a 120 volt 60 Hz AC P Grounding only 15 Ampere or more fused electrical supply It is rec 3 Pronged Plug ommended that a separate circuit serving only this appliance be provided When installing this appliance observe all applicable codes and ordinances em 4 WARNING improper use of the grounding plug can 4 SE result in a risk of electric shock GE Gs aD tor 3 Pronged Receptacle Grounding Screw Where a two pronged wall receptacle is encountered it is the personal responsibility and obligation of the cus tomer to contact a qualified electrician and have it re placed with a properly polarized and grounded three pronged wall receptacle or use a grounding adaptor If an extension cord must be us
55. on the oven to avoid touch ing the high voltage transformer or unplug the primary terminal connector of the high voltage transformer to turn it off the end of such connector must be insulated with an insulating tape After servicing be sure to re connect the leads to their original locations 1 On some models the power supply cord between the touch control panel and the oven itself is so short that 25 the two can t be separated For those models check and repair all the controls sensor related ones in cluded of the touch control panel while keeping it connected to the oven 2 On some models the power supply cord between the touch control panel and the oven proper is long enough that they may be separated from each other For those models therefore it is possible to check and repairthe controls of the touch control panel while keeping it apart from the oven proper in this case you must short both ends of the door sensing switch on PWB of the touch control panel with a jumper which brings about an operational state that is equivalent to the oven door being closed As for the sensor related controls of the touch control panel checking them is possible if dummy resistor s with resistance equal to that of the controls are used Servicing The Touch Control Panel With An External Power Supply Disconnect the touch control panel completely from the oven proper and short both ends of the door sensing switch on PWB of
56. r the oven while using Sensor settings The sensor will detect the vapor given off by the spray and turn off before the food is properly cooked 8 If the sensor has not detected the vapor of the food ERROR will appear and the oven will shut off Water load cooking test Note The cabinet should be installed and screws tightened Make sure the oven has been in lease five minutes before checking sensor cook opera tion 1 Fill approximately 200 milliliters 7 2 oz of tap water in a 1000 milliliter measuring cup 2 Place the container on the center of tray in the oven cavity 3 Close the door 4 Touch SENSOR REHEAT pad once Now the oven is in the sensor cooking condition and SOR REHEAT will appear in the display 5 Now the oven will operate for the first 16 seconds without generating microwave energy Note ERROR will appear if the door is opened or STOP CLEAR button is touched during first stage of sensor cooking 6 After approximately 16 seconds microwave energy is produced the oven should turn off when water is boiling bubbling If the oven does not turn off replace the AH sensor or check the control unit Testing Method for AH Sensor and or Control Unit To determine if the sensor is defective the simplest method is to replace it with a new sensor Disconnect the power supply cord and then remove outer case cabinet Open the door and block it open Discharge the high voltage capacitor
57. re de en ergized and the power transformer oven lamp etc are turned off 6 By opening the door or touching the STOP CLEAR pad the time of day will re appear on the display and the oven will revert to an OFF condition R 420BK R 420BW DESCRIPTION AND FUNCTION OF COMPONENTS Cooling Fan Motor The cooling fan motor drives a blade which draws exter nal cool air This cool air is directed through the air vanes surrounding the magnetron to cool the magne tron This air is channeled through the oven cavity to re move steam and vapors given off from the heating foods Itis then exhausted through exhaust vents in the oven cavity Oven Temperature Fuse The oven temperature fuse located on the top of the oven cavity is designed to prevent damage to the unit if the foods in the oven catch fire due to over heating pro duced by improper setting of cook time or failure of con trol unit Under normal operation the oven temperature fuse re mains closed However when abnormally high temper atures are reached within the oven cavity the fuse will open at 144 C causing the oven to shut down Note This is a fuse and it does not reset Magnetron Temperature Fuse The magnetron temperature fuse located on top of the magnetron duct is designed to prevent damage to the magnetron if an over heated condition develops in the tube due to cooling fan failure obstructed air ducts dirty or blocked air intake etc Under normal operation
58. resistance of the filament coil should be less than 10 5 Reconnect all leads removed from components during testing 6 Re install the outercase cabinet 7 Reconnect the power supply cord after installing the outer case cabinet 8 N N ON O gt Run the oven and check all functions ote High voltages are present at the high voltage terminal so do not attempt to measure the fila ment and high voltage 11 R 420BK R 420BW TEST PROCEDURES Procedure Letter Component Test C High Voltage Rectifier Test Disconnect the power supply cord and then remove outer case cabinet Open the door and block it open Discharge the high voltage capacitor Isolate the rectifier from the circuit Using the highest ohm scale of the meter read the resistance across the terminals and observe reverse the leads to the rectifier terminals and observe meter reading If a short is indicated in both directions or if an infinite resistance is read in both directions the rectifier is probably defective and should be replaced 5 Reconnect all leads removed from components during testing 6 Re install the outer case cabinet 7 Reconnect the power supply cord after installing the outer case cabinet 8 Run the oven and check all functions Note Be sure to use an Ohm Meter that will supply a forward bias voltage of more than 6 30 Volts D High Voltage Capacitor Test Discharge the high voltag
59. robe signal Signal applied to touch key section A pulse signal is inputted to P43 P46 terminal while one of G6 line keys on key matrix is touched P24 OUT Key strobe signal Signal applied to touch key section A pulse signal is inputted to P43 P46 terminal while one of G5 line keys on key matrix is touched P23 OUT Key strobe signal Signal applied to touch key section A pulse signal is inputted to P43 P46 terminal while one of G4 line keys on key matrix is touched P22 OUT Key strobe signal Signal applied to touch key section A pulse signal is inputted to P43 P46 terminal while one of G3 line keys on key matrix is touched P21 OUT Key strobe signal Signal applied to touch key section A pulse signal is inputted to P43 P46 terminal while one of G2 line keys on key matrix is touched 0 _ P20 OUT Key strobe signal Signal applied to touch key section A pulse signal is inputted to P43 P46 terminal while one of G1 line keys on key matrix is touched OUT c G CO 41 44 P17 P14 cO 23 R 420BK R 420BW PinNo Signal VO Description S 45 51 5EG27 SEG21 OUT Segment data signal Connected to LCD The relation between signals are as follows LSI signal Pin No LCD Pin No LSI signal Pin No LCD Pin No SEG 27 45 516 25 SEG 13 59 S20 12 SEG 26 46 S15 24 SEG 11 61 EE S21
60. ry interlock switch fail to open when the door is opened Monitor Switch Functions 1 When the door is opened the monitor switch con tacts close to the ON condition due to their being normally closed At this time the primary interlock relay and secondary interlock switch are in the OFF condition contacts open due to their being normally open contacts 2 Whenthe dooris closed the monitor switch contacts are first opened and then the door sensing switch and the secondary interlock switch contacts close Note When opening the door each of these switches operate inversely 3 If the door is opened and the primary interlock relay and secondary interlock switch contacts fail to open the monitor fuse blows simultaneously with closing of the monitor switch contacts CAUTION Before replacing a blown monitor fuse test the prima ry interlock relay door sensing switch monitor switch and secondary interlock switch for proper operation Refer to section Test Procedures Door Sensing Switch Latch Heads Monitor witch Secondary Interlock Switch TA Or NOTE MONITOR FUSE AND MONITOR SWITCH ARE REPLACED AS AN ASSEMBLY R 420BK R 420BW SERVICING When troubleshooting the microwave oven it is helpful to follow the sequence of operation in performing the checks Many of the possible causes of trouble will require that a specific test be performed These tests are given a procedure letter
61. switches indicator and vents While testing for leakage around the door pull the door away from the front of the oven as far as is per mitted by the closed latch assembly 4 Measure carefully at the point of the highest leakage and make sure that the highest leakage is no greater than 4 mW cm to allow for measurement uncertainty and that the secondary interlock switch does turn the oven OFF before any door movement Note After servicing record data on service invoice and microwave leakage report R 420BK R 420BW EE ENEE eg E 2 eJIM eut p o uuoo eq 5 1exoos due jeuiuue 79 eut peura peaj eut pejoeuuoo eq 1snui JOY eu 76 s uln ye ye eq Melos p109 Addne r Oym ALI jenou eui pejoeuuoo eq snw Ajddns synoi jou syno oj epoo 72 o lqns syno L eDu amp JO OHO umo NYG eme mw SALON 0 AWD NHO HOLIMS 5 X20 1H31NI 9 ON AHVOINOO3S SZ O Es IHM 1HM 1HM LHM AYD O WOO NH E HOLIMS HOLINOIN 2 HOLIMS ON ONISN3S Hood
62. t adhesive tape on the backing film of the sealer film as shown below 2 Tear the backing film by pulling the adhesive tape 3 Put the pasted side of the sealer film on the door pan el Sealer film Backing film J Adhesive tape R 420BK R 420BW ABSOLUTE HUMIDITY SENSOR CIRCUIT Structure of Absolute Humidity Sensor The absolute humidity sensor includes two thermistors as shown in the illustration One thermistor is housed in the closed vessel filled with dry air while another is in an open vessel Each sensor is provided with a protective cover made of metal to protect it from the external air flow The open vessel cover has two small holes in it to allow moisture laden air from the oven cavity to surround it Thermistors Sensing part Sensi rt Open vessel db ds Closed vessel ventilation openings for sensing Operational Principle of AH Sensor The figure below shows the basic structure of an abso lute humidity sensor A bridge circuit is formed by two thermistors and two resistors R1 and R2 The output of the bridge circuitis amplified by an opera tional amplifier Each thermistor is supplied with a current to keep it heated to about 150 C 302 F and the resultant heat is dissipated in the air if the two thermistors are placed in different humidity conditions they show different hu midity conditions and different degrees of heat conduc tivity leading to a potential difference between
63. t the power supply cord after installing the outer case cabinet Run the oven and check all functions N ONO OQ E Reheat Popeom Baked Fresh KITCHEN 7 Potato Vegetables TIMER MINUTE chicken Chicken R FROZEN Fresh Ground Power Ice PLUS breast reng vi STAND Leve Frozen St eaks Frozen Ground meat START Auto Start Roll Ch entrees COMPU Clock Muffin ops DEFROST 18 R 420BK R 420BW TEST PROCEDURES Procedure Letter Component Test L AH Sensor Test Checking the initial sensor cooking condition 1 The oven should be plugged in at least five minutes before sensor cooking 2 Room temperature should not exceed 95 F 35 C 3 The unit should notbe installed in any areas where heat and steam are generated The unit should not be installed for example next to a conventional surface unit 4 Exhaust vents are provided on the bottom of the unit for proper cooling and air flow in the cavity To permit adequate ventilation be sure to install so as not to block these vents There should be some space for air circulation 5 Be sure the exterior of the cooking container and the interior of the oven are dry Wipe off any mois ture with a dry cloth or paper towel 6 The sensor works with food at normal storage temperature For example chicken pieces would be at refrigerator temperature and canned soup at room temperature 7 Avoid using aerosol sprays or cleaning solvents nea
64. tact with the following parts may result in severe possibly fatal electric shock Example High Voltage Capacitor Power Transformer Magnetron High Voltage Rectifier Assembly High Voltage Harness etc WARNING Avoid pos S bis exposure to microwave energy Please follow the instructions below before operating the oven 1 Disconnect the power supply cord 5 There are defective parts in the door interlock SS 2 Visually check the door and cavity face plate for tem damage dents cracks signs of arcing etc 6 There are defective parts in the microwave gener Carry out any remedial work that is necessary before ating and transmission assembly operating the oven 7 There is visible damage to the oven Do not operate the oven if any of the following condi tions exist Do not operate the oven 1 Door does not close firmly 1 Without the RF gasket Magnetron 2 Door hinge support or latch hook is damaged 2 If the wave guide or oven cavity are not intact 3 The door gasket or seal is damaged lf the door is not closed 4 The door is bent or warped 4 If the outer case cabinet is not fitted WARNING FOR WIRING To prevent electric shock take the following pre er and oven cavity SEHR 3 Sharp edge 1 Before wiring Bottom plate oven cavity waveguide flange 1 Disconnect the power supply cord chassis support and other metallic plate 2 Open the door and block it open 4 Movable parts to prevent a f
65. tently through the contacts of relay RY 2 which is oper ated by the control unit within a 32 second time base Mi crowave power operation is as follows Vari Mode P HI HIGH 100 power P 90 approx 90 power P 80 approx 80 power P 70 MED HIGH approx 70 power P 60 approx 60 power P 50 MED approx 50 power P 10 approx 10 power 6 sec 26 sec 0 0 power 0 sec 32 sec The ON OFF time ratio does not correspond with the percentage of microwave power because approximate ly 2 seconds are needed for heating the magnetron fila ment P 40 approx 40 power P 30 MED LOW approx 30 power P 20 approx 20 power R 420BK R 420BW OPERATION DESCRIPTION OF OPERATING SEQUENCE The following is a description of component functions during oven operation Sensor Cooking Condition When using the SENSOR REHEAT function the foods are cooked without figuring time power level or quantity When the oven senses enough steam from the food it relays the information to its microprocessor which will calculate the remaining cooking time and the power lev el needed for best results When the food is cooked water vapor is developed The sensor senses the vapor and its resistance increases gradually When the resistance reaches the value set according to the menu supplementary cooking is started The time of supplementary cooking is deter
66. that is the connecting lead of the high voltage rectifier against the chassis with the use of an insulated screwdriver Whenever troubleshooting is performed the power sup ply must be disconnected In some cases it may be nec essary to connect the power supply after the outer case has been removed in this event 1 Disconnect the power supply cord and then remove outer case cabinet 2 Open the door and block it open 3 Discharge the high voltage capacitor 4 Disconnect the leads to the primary of the power transformer 5 Ensure that the leads remain isolated from other components and oven chassis by using insulation tape 6 Afterthe above procedure reconnect the power sup ply cord Don t Touch Danger High Voltage When the testing is completed 1 Disconnect the power supply cord and then remove outer case cabinet Open the door and block it open Discharge the high voltage capacitor Reconnect the leads to the primary of the power transformer 5 Re install the outer case cabinet 6 Reconnect the power supply cord after the outer case cabinet is installed 7 Start the oven and check all functions After repairing 1 Reconnect all leads removed from components dur ing testing 2 Re install the outer case cabinet 3 Reconnect the power supply cord after the outer case is installed 4 Reconnect the power supply cord after the outer case is installed 5 Run the oven and check all funct
67. the touch control panel which acti vates an operational state that is equivalent to the oven door being closed Connect an external power source to the power input terminal of the touch control panel then it is possible to check and repair the controls of the touch control panel it is also possible to check the sen sor related controls of the touch control panel by using the dummy resistor s Servicing Tools Tools required to service the touch control panel assem bly 1 Soldering iron 30W It is recommended to use a soldering iron with a grounding terminal 2 Oscilloscope Single beam frequency range DC 10MHz type or more advanced model 3 Hand tools Other Precautions 1 Before turning on the power source of the control unit remove the aluminum foil applied for preventing static electricity 2 Connect the connector of the key unit to the control unit being sure that the lead wires are not twisted 3 After aluminum foil is removed be careful that abnor mal voltage due to static electricity etc is not applied to the input or output terminals 4 Attach connectors electrolytic capacitors etc to PWB making sure that all connections are tight 5 Be sure to use specified components where high pre cision is required R 420BK R 420BW COMPONENT REPLACEMENT ADJUSTMENT PROCEDURE WARNING AGAINST HIGH VOLTAGE Microwave ovens contain circuitry capable of producing very high voltage and current con
68. them causing an output voltage from the bridge circuit the in tensity of which is increased as the absolute humidity of the air increases Since the output is very minute it is amplified by the operational amplifier Operational Amplifier Output voltage Absolute humidity vs output voltage characteristic Output voltage S Thermistor open vessel C Thermistor closed vessel Absolute humidity g m3 Detector Circuit of AH Sensor Circuit This detector circuit is used to detect the output voltage ofthe absolute humidity circuit to allow the LSI to control 32 the sensor cooking of the unit When the unit is set in the sensor cooking mode 16 sec onds later the detector circuit starts to function and the LSI observes the initial voltage available at its AN1 ter minal With this voltage given the switches SW1 to SW5 in the LSI are turned on in such a way as to change the resistance values in parallel with R107 R111 of IC2 Changing the resistance values results in that there is the same potential at both the F 3 terminal of the abso lute humidity sensor and the ANO terminal of the LSI The voltage of AN1 terminal will indicate about 2 5V This initial balancing is set up about 16 seconds after the unit is put in the Sensor Cooking mode As the sensor cooking proceeds the food is heated to generate moisture by which the resistance balance of the bridge circuit is deviated to increase the voltage availabl
69. transformer oven lamp and cooling fan are turned off and the generation of microwave energy is termi nated 6 When the door is opened during a cook cycle the monitor switch door sensing switch secondary in terlock switch and primary interlock relay are acti vated with the following results The turntable motor cooling fan motor and the high voltage components are de energized The oven lamp remains on and the digital readout displays the time still remaining in the cook cycle when the door was opened 7 The monitor switch is electrically monitoring the op eration of the secondary interlock switch and primary interlock relay and is mechanically associated with the door so that it functions as follows a When the door opens from a closed position the secondary interlock switch and primary interlock relay open their contacts then the monitor switch contacts close b When the door is closed from the open position the monitor switch contacts first open and the contacts of the secondary interlock switch close If the secondary interlock switch and the primary inter lock relay contacts are closed when the door is opened the monitor switch contacts form a short circuit through the monitor fuse secondary interlock switch and prima ry interlock relay causing the monitor fuse to blow Power Level P 0 to P 90 Cooking When Variable Cooking Power is programmed 120 volts AC is supplied to the power transformer intermit
70. w the water to heat 3 Remove the cup from the oven and again measure the temperature making sure to stir the ther mometer or thermocouple through the water until the maximum temperature is recorded 4 Subtract the cold water temperature from the hot water temperature The normal result should be 38 to 78 F 21 to 42 6 C rise in temperature If the water temperatures are accurately mea sured and are tested for the required time period the test results will indicate if the magnetron tube has low power output low rise in water temperature which would extend cooking time or high power output high rise in water temperature which would reduce cook time Because cooking time can be adjusted to compensate for power output the magnetron tube assembly should be replaced only if the water temperature rise test indicates a power output well beyond the normal limits The test is only accurate if the power supply line voltage is 120 volts and the oven cavity is clean B Power Transformer Disconnect the power supply cord and then remove outer case cabinet Open the door and block it open Discharge the high voltage capacitor Disconnectthe primary input terminals and measure the resistance of the transformer with ohm meter Check for continuity of the coils with an ohmmeter On the R X 1 scale the resistance of the primary coil should be less than 1 2 andthe resistance of the high voltage coil should be approx imately 1000 the
71. y checks on all ovens to be serviced before activating the magnetron or other microwave source and make repairs as necessary 1 Interlock operation 2 proper door closing 3 seal and sealing surfaces arcing wear and other damage 4 damage to or loosening of hinges and latches 5 evidence of dropping or abuse c Before turning on microwave power for any service test or inspection within the microwave gen erating compartments check the magnetron waveguide or transmission line and cavity for proper alignment integrity and connections d Any defective or misadjusted components in the interlock monitor door seal and microwave generation and transmission systems shall be repaired replaced or adjusted by procedures described in this manual before the oven is released to the owner e A microwave leakage check to verify compliance with the Federal Performance Standard should be performed on each oven prior to releasing oven to the owner RD21101U BEFORE SERVICING Before servicing an operative unit perform a microwave emission check as per the Microwave Measurement Procedure outlined in this service manual If microwave emissions level is in excess of the specified limit contact SHARP ELECTRONICS CORPORATION immediately 1 800 237 4277 If the unit operates with the door open service person should 1 tell the user not to operate the oven and 2 contact SHARP ELECTRONICS CORPORATION and DHHS immediately Servic

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