SM_EMS1053_1563_35532.17 MB
Contents
1. 4 The food can be heated but the turntable tray is not rotating The turntable motor broken The plug fall off Connecting shaft weave broken Change the turntable motor Inset the plug securely Change the weave 5 The oven can heat within 2 3 minutes but can not heat from the fourth minutes The winding of the fan motor in open circuited The fan falls off The plug of the fan motor falls off The turnatable shaft is griped with the mo tor bearin The cooling vent blocked 1 Change the fan motor 2 Change the fan 3 Insert the plug 4 Overhauling them 5 Repairing it 6 When starting the oven it can t heat and with wenwen noise The high voltage diode was punctured Change a new diode 7 The oven can heat but with sound shishi noise The iron core of the transformer loosed Change a new transformer 8 Large amount of microwave leakage The door deformed The door metal net cracked The gap of the door crack is too large The welding point of the oven falls off The screws which fix the magnetron loosed The wave guide connection oxidized The magnetron copper filament washer is too thin cause the wave guide opening not in good earth Mend the door Change the door Adjust the gap Change the oven Tighten the screws Scrape the oxidized and tighten the screws Thick the copper filament washer 9 The door can t open After long time using the wear and the rust2. If there still exist microwave leakage measure near the magnetron with the probe of the microwave leakage mea sure If A the leakage is larger the oven should be turned off and check 00000 whether the four screws which fix the magnetron have been loosed if loosed twist them tightly with socket wrench If the four screws are fixed then the magnetron should be taken down to va e check the copper filament weaved washer of the magnetron has A been placed well or whether the wave guide housing coupling 6060 ES has been oxidized or have lacquer on it If do have scrape the oxidized layer or the lacquer off When fix the magnetron the copper filament weaved washer must be placed well the screws must be twist tightly Then turn on the oven and measure again until it comply with the requirement If the microwave leakage is larger at those hole position of the window board The oven should be turned off to inspect whether there are crack among them fig 5 16 If several holes formed a crack it would enlarge the microwave leakage If that is the case it indicates the door has broken and should be replaced with a new door 2 Means of repair when the oven can heat but the turntable glass can t move Firstly check whether the turntable holder is placed correctly If it is correct then pull out the power plug and take down the turntable combination measure the resistance value of the turntable motor Rx1K grade o
3. fan SCTew Fig 4 14 Fig 4 13 4 7 THE CAPACITOR Firstly do as the 1 2 3 steps of of this part To disassemble 1 Pull the wires of the capacitor out 4 15 as J 2 Loosen and take out the screw which fix the capacitor clip ie A gt ne with a screwdriver and take out the clip and the capacitor 4 15 diode 4 lt L k screw Vy To assemble 1 Place the capacitor in the capacitor clip with the end which have three foot near the diode 4 16 2 Insert one end of the clip in the fan holder trough FIG 4 15 3 Tighten the screw which fix the capacitor clip Fig 4 15 4 Plug in all the plugs of the capacitor 4 8 THE DIODE magnetron Firstly do as the 1 2 3 steps of of this part capacitor H V fuse gs To disassemble D transformer 4 Pull out the diode plug which plugged in the capacitor 2 Loosen the screw which fixed the diode and take the diode off Fig 4 16 To assemble 1 Insert one end of the diode to one feet of the capacitor s connect piece 2 Fix the diode with one screw pay attention to the polarity of the diode refer to FIG 4 16 4 9 THE TURNTABLE COMBINATIOM eae Firstly do as the 1 2 3 stops of of this part i To disassemble 1 Turn the microwave oven over FIG 4 17 2 Take off the two screws which fix the middle base board with a screwdriver and take off the middle cover FIG 4 18 3 Loosen out the
4. eaten enlarged the gap of the door shaft and the shaft hole thus cause the door crooked The door hook broken Adjust the hinge to rectify the position of the door Change the hook 10 The door button fall off release Worn out time operating and aged after long Overhaul it or renew it 22 The earthing insulation resistance of all the 11 Electricity leaking motors or the transformer are less than 2 megaohms Test where is the leaking place then repair it or change those damaged components Attachment Y y y yyy Ye ve Vv vw EM S1053 explore view and parts list EM G2053 explore view and parts list EM S1553 explore view and parts list EM G2553 explore view and parts list EM S1063 explore view and parts list EM G2063 explore view and parts list EM S1563 explore view and parts list EM G2563 explore view and parts list EM S3553 explore view and parts list EM G4753 explore view and parts list 23
5. then push the door close to the oven and tighten the two screws of the hinge UP and paint them THE CONTROL PANEL AND THE DOOR RELEASE D MECHANISM eee alle 10 Fig 4 6 Take off the cabinet Discharge between one end of the capacitor and the baseboard with a screwdriver To disassemble 1 Pull out the terminal plug of the time and power distributor 2 Take off the screw which fix the control panel with a screwdriver FIG 4 6 3 Take off the control panel To assemble 1 Place the two buckles under the control panel into the two rectangle holes under the oven as FIG4 6 then make close of the control panel and the oven with being fixed with a screw Plug in the terminal plug 4 4 THE MAGNETRON Firstly do as 1 2 3 steps at of this part To disassemble 1 Take off the screw beside the oven lamp FIG 4 8 2 Take out the four screws which fixed the magnetron and take the magnetron off FIG 4 7 SCrewe _magnetron Gy ee LR a screwe j x 7 magnetron thermal cutout NG tet A magnetron holder magnetron holder S5 Z lt 7 N SK N J D lamp shade y Fig 4 8 Fig 4 7 To assemble the magnetron 1 Check whether the copper filament weaved washer of the magnetron antenna has been placed well It should not be fixed if there is no copper filament weaved washer for it may cause the magnetron and the oven can t earth well and cause large amount of microwave
6. avometer can t point out from zero to nine megaohms it secondary winding indicates the high voltage capacitor has broken and should DN be replaced by a new one If it is normal between the two pole of the capacitor then the insulation between the capacitor pole and the cabinet should be measured with Rx10K grade of an avometer The S resistance value should be FIG5 12 If it is short CEE se circuited or have a number reading it indicates that the a capacitor has been punctured or electricity leaked and should be replaced by a same model same capacity one Fig 5 9 transformer primary winding A capicitor capacitor Fig 5 10 Fig 5 11 Fig 5 12 If the resistance value of the capacitor s two pole are the capacitor is normal Then check the earth of the magnetron s two filaments to see whether they are short circuited FIG 5 13 If they are short circuited and the filament strikes the shell of the magnetron it indicates the magnetron magnetron has broken and should be replaced by a new lt same model one If the magnetron is also normal then test the pilot switch Pull out the two plugs of the switch Measure it with the Rx1 grade of avometer the two rod connect the plug of the switch the resistance value should be FIG 5 8 Then press down the pilot switch with a screwdriver if the reading of the avometer pointed to zero it indicates the pilot switch ha
7. check whether the door is flexible If it does back and front position of the holder should be adjusted Provided the up hook is loose the door should be pushed more closely to the oven and pull the holder inside closely after loosen the screw which fix the holder then tighten the screw and check whether it is still loose If it is not or the loose is minor it would be OK Open the door then close it lightly check whether the hook is in position if not readjustment is needed If the loose is at lower part of the door the adjust methods is the same with the above said 14 Screw y latch switch holc front door pl Fig 4 21 steps but the screw is the one below FIG4 21 4 11 THE CONTROL PANEL OF A TYPICAL MICROWAVE OVEN Pull out the power plug Take off the cabinet CL 7 light tough switch Discharge between one end of the capacitor and the i 1 EC board baseboard with a screwdriver control panel Means of dismantling the PC board and door release N mechanism MIT I US C 1 Pull out all the terminal plug of the PC board ine IC es i 2 Loosen out the two screws which fix the control panel with a screwdriver FIG 4 6 3 Take off the control panel 4 Take off the three screws which fix the PC board as the FIG 4 22 Fig 4 22 5 Take off the range terminal plugs as FIG 4 24 shown that is press the two places according to the arrow direction at the figure while
8. felt on it If the felt are soaked with kerosene then the engine oil can not be sucked up After the bearing being cleaned the felt should be refueled fully with engine oil for when the oven is operating the engine oil empty into the oil bearing slowly Fix the bearing cover with two screws turn the fan around till it can move flexibly Then install them to the oven and plug in the two terminal plugs If the fan can move flexibly then the winding of the fan motor should be examined Measure the winding with Rx100 grade of a avometer if it is open circuited it indicates the winding of the fan motor has broken and should be re placed by a new same model one 5 4 THE CHARACTERS REQUIREMENTS OF MICROWAVE AFTER IT HAS BEEN REPAIRED After being repaired the microwave oven should have a 30 minutes trial operation It can be used only when it has been demonstrated that it is in good conditions of safety heating and defrosting The oven must have the following identifications when it at trial operating 5 4 1 INSULATION Before conducted measure the insulation resistance among those electric metal parts and the nonelectric metal cabinet with a 500V D C Megaohmmeter The resistance value should not be less then 2 megaohm Testing condition Door closed power at high time set at 3 minutes This is the operating condition of the oven but the power plug is not connected 5 4 2 MICROWAVE LEAKAGE Microwave leakage can not be
9. leakage Attention When a new oven matches a magnetron the meatl lustre at mark should be polished with a sand paper FIG 4 7 2 Aim the head of the magnetron antenna to the hole of the wave guide housing tighten the four screws of the magnetron vertically and also tighten the screws of the lampshade FIG 4 8 3 Plugin the two terminals of the magnetron filament and the thermal cutout 4 5 THE TRANSFORMER Firstly do as the 1 2 3 steps at of this part Dismantling steps for the transformer as FIG 4 9 1 Pull out all the terminal of the transformer 2 Turn the microwave over 3 Take off the right baseboard with the transformer after loosened the four screws which fix the board on the oven 4 10 4 Take off the four screws a b c d with a screwdriver LL 5 Take off the right baseboard the seat and the rubber space between the transformer and the oven A IN screw base board transformer seat x Fig 4 10 Fig 4 9 to mount the transformer 1 Place the transformer as the FIG 4 9 tear off the protective paper of the rubber lining tape stick it on the transformer as shown on the figure Then put on the seat and the right base board make sure the screw hole are tallied then tighten the four screws for the high voltage winding is earthing here 2 Fix the transformer on the oven as FIG 4 10 tear off the protect paper of the rubber spacer set it between the transformer and the oven
10. make sure the adhesive side is sticked on the oven 3 Plugin all the terminals of the transformer precisely 4 6 THE FAN MOTOR Firstly do as the 1 2 3 steps of of this part To disassemble 1 Pull out the two terminal of the fan motor FIG 4 11 2 According to the FIG 4 12 pull out the lead plug which marked A and C from the thermal cutout and the fuse housing separately and take off the earthing screw which marked B FIG4 12 fan motor z _ power supply cord 3 Take out the power supply cord from the trough as the figure shows Fig 4 11 4 Loosen the screws shown on the FIG4 13 with a screwdriver and take off the fan holder 5 Take off the fan from the fan motor shaft as F1G 4 14 then the fan motor to mount the fan motor 1 Assemble the fan motor as FIG 4 14 Drip the glue on the place of the fan motor shaft and fix the fan on the A earthing screw motor make sure it must be fixed to the bottom of the a a shaft Attention The fan motor shaft should not be curved lt i Pa the fan should have no abnormal stick up After assembled check whether the running fan would knock the fan holder 2 Assemble the fan holder as FIG 4 13 Then connect the power supply cord with the two wires of the fan motor and Gita ae P tighten the screws as FIG 4 11 and FIG 4 12 ee supply cord Fig 4 12 12 7 J AK fan motor Pack board
11. pull it up about 2mm then off the row plastic board light tough switch A 6 Take off the PC frame 7 Tear off the undried glue of the light touch switch FIG 4 23 to assemble the PC board and door release mechanism control panel 1 Tear off the undried glue patch of the light tough switch 1 and 2 as the Fig shown and place them into the rectangle hole of the surface of the plastic board 2 After uprighted the light tough switch tear off the protective paper on the back and stick it on the plastic board smoothly Fig 4 23 3 Tear off the protective paper of the light touch switch 2 and stick the switch on the back of the plastic board smoothly 4 Assemble in the PC frame and PC board as FIG 4 22 and fix them with three screwes T 5 Fix the range wires as FIG 4 24 the means are Insert the range wires first make sure that its notch is tallied with 0 U L the flange of the row seat then press it down to its normal position 6 Fix the control panel on the oven FIG 4 6 7 Plug in the terminal plugs of the PC board Fig 4 24 5 BREAKDOWN ANALYSIS AND THE MEANS OF OVERHAULING Before overhauling a microwave oven you should judge the breakdown and the cause correctly then you can repair it with corresponding ways The overhauling must be proceed in order any hasty conclusion is not recommendable otherwise over working would be done when repair The
12. tell by watching or touching To be responsible for the user the amount of microwave leakage should be measured strictly and should not exceed 5 milliwatt cm2 according to the IEC STANDARD Some countries stipulate that the maximum microwave leakage should not exceed 1 milliwatt cm2 For safety concern we must control the leakage under 1 milliwatt cm2 after the oven being repaired otherwise it should be repaired again Test must be proceeded completely and comply with the following procedures Put a graduate of about 275ml water at the middle of the turntable glass tray of the oven insert the power plug close the door power set high time set 3 minutes to make the oven in operation Rectify the microwave leakage measure first measure around the door crack the metal net of the door and the air vent with the probe of the measure when measuring the moving speed of the probe should not exceed 25mm sec The measuring direction of the probe must be the same with the outgoing direction of the microwave leakage 5 4 3 MICROWAVE HEATING Place a graduate of about 250ml water on the turntable tray Close the door power set high time set 4 minutes To those 700W microwave oven to make the oven operating in normal When the bell of the timer rings open the oven door the water should have boiled If it have not been boiled yet but is very hot check whether the voltage is less than 230V If the voltage below 230V but the water can be boiled after a li
13. the magnetron working internally at the same working point to change the output of the magnetron This method was called CONDUCTION RATIO CONTROL But there is another method which is called ELECTRIC LEVEL CONTROL which is through changing the working point such as anode voltage or magnetic field to change the output of the magnetron Because of conduction ratio control method is low cost high function and high reliability it is widely used for those microwave oven which have the power control function 230V S4 Ss Fig 2 6 FIG 3 1 is the power control circuit diagram of brand microwave oven WP700 This is a typical instance of conduction ratio control This oven adopt time and power controller as a whole When a 230V 50Hz alternating current is inputted the time and power motor is always at working condition At the FIG 2 7 S5 is always conducted Made the S5 working 30 seconds as a circle the conduct time can be successively adjusted from 5 seconds to 30 seconds When power select switch is set at HIGH S5 is always conducted the output of the microwave oven is 700W full power when the power select switch is set at defrost position S5 would conduct for 14 4 seconds and cut off for 15 5 seconds and the average output of the oven is 336W 2 4 3 THERMAL CUTOUT Thermal cutout actually is a thermal sensor switch usually it is fixed on the shell of the magnetron and series connected with the primary circuit of t
14. two screws of turntable motor with a screwdriver take out the turntable motor and pull out the two 13 Fig 4 17 wires 4 17 Assembling steps 1 Put the motor shaft into its connecting hole and fix the motor with two screws FIG 4 17 2 Plug in the two wires 3 Assemble and fix the middle base board with two screws FIG 4 18 Turn the oven back As the FIG 4 19 shown fix in the turntable shaft supporter the place in the roller ring and the glass tray as FIG 4 20 s turntable shaft supporter r 25 roller ring Fig 4 19 4 10 THE DOOR SAFTY INTERLOCKS Firstly do as the same with 1 2 3 steps of of this part Steps for dismantling 1 Pull out the terminal plugs of the interlock switch and the pilot switch Fig 4 18 2 Loosen out the two screws which fixed the switch holder with a screwdriver and take the switch holder off 3 Take off the interlock switch and the pilot switch from the holder 4 Take off the switch connecting lever arm and the working lever from the holder Assembling steps 1 Slip on the connecting lever arm and the working lever into the switch holder 2 Assemble the interlock switch and pilot switch to the switch holder make sure they are assembled correctly 3 Tightly fix the holder with two screws 4 Check the position of the hook and the switch holder Close the door push and pull the low and up part of the door to
15. BREAKDOWN OF MICROWAVE OVEN AND MEANS OF REPAIRING PHENOMENON CAUSE REPAIRING MEANS 1 When starting the 8A fuse broken Change a new fuse oven the lamp is not on wnat th turntable tray can t The primary and secondary winding of the Change a new TORAORIER rotate and the food can t transformer are short circuited Change a new capacitor be heated The earthing or the polarity of the polarity of Change a new pilot switch 21 the capacitor is punctured The pilot switch can t cut off The interlock switch hasn t closed The power plug and the socket are not in good connection The door hook broken Change a interlock switch new Adjust the connection or replace it by a new one Change a new hook 2 When starting the oven the lamp is on the turntable rotating the fan cycling but the food can t be heated The primary and secondary winding the filament of the transformer are open circuit ed The magnetron filament is open circuited the magnetic steel of the magnetron broken or the magnetron is air leaking Time and power distributor broken The plugs of the magnetron or the capacitor loosed Change a new transformer Change the magnetron Change the time power distributor or the micro switch Fix them 3 The food can be heated but the lamp is not on The lamp broken The plug falls off Change a new lamp Insert the plug again
16. M year e aa ete hee ite A de AAA 5 2 4 ELECTRIC CONIROLSTSTEM riso Tianara A E E E AA 5 3 TYPICAL CIRCUIT ANALYASIS OF MICROWAVE OVEN LL iiiirreereeeeeeeeeennnes 8 4 HOW TO ASSEMBLE AND DISASSEMBLE MICROWAVE OVEN COMPONENTS seeen 9 4 1 THE CABINET RSS Sn E EE ace cee E ea ara A 9 TRE DOOR COMBINATIONS mre a E E an eth tenn 9 4 3 THE CONTROL PANEL AND THE DOOR RELEASE MECHANISM 10 4 4 THE MAGNE TRON rinna a EEN E A E 11 4 5 aa EEE E E Ae ee E E EE E een 11 4 6 THE FAN MOTOR 3 cee AEEA dt EEA ie eee E 12 4 7 THE CAPACITOR afore reaa r AO ten Mr a itn eee Mogae a 13 4 8 THE DIODE 255 ren A SET a EAA Ade den et a KADE DEA TAEA an 13 4 9 THE TURNTABLE COMBINATIOM iii 13 4 10 THE DOOR SAFTY INTERLOCKS ienei ninii eee eben eei tii eain eee Let etre to tn 14 THE CONTROL PANEL OF A TYPICAL MICROWAVE OVEN ccecccceeeeceeeeeeneeeeeeneeeeeeaeeeeeenaeeeeeeeneeeenenaes 15 5 BREAKDOWN ANALYSIS AND THE MEANS OF OVERHAULING in 15 5 1 EXAMINING THE BREAKDOWN CAUSES 0 000 cececceeeeeeeeeeeeeeeeeeeeeeeeeeneaeeeeeneaeeeeeneaeeeteeeaeeeeeeaeees 15 SPOT EXAMINING STEPS OF THE MICROWAVE OVEN ire 16 5 3 REPAIRING METHOD OF SEVERAL BREAKDOWN in 18 5 4 THE CHARACTERS REQUIREMENTS OF MICROWAVE AFTER IT HAS BEEN REPAIRED 20 6 CRITICAL PARTS SERVIGING earen ne rte Mt dm ln te naar durera de nd dt antenne Mere Teens 21 6 1 IMPORTANT THINGS TO DO PRIOR TO CRITICAL PARTS SERVICING 21 6 2 Interlock Assembly Replacement and Adju
17. RMATION CONTAINED IN IT IS TO BE USED ONLY BY AN AUTHORIZED SERVICE TECHNICIAN FAMILIAR WITH AND KNOWLEDGEABLE OF PROPER SAFETY AND SERVICING PROCEDURES AND POSSESSING HIGH QUALITY TEST EQUIPMENT ASSOCIATED WITH MICROWAVE AND ELECTRICAL APPLIANCE REPAIR ALL INDIVIDUALS WHO ATTEMPT REPAIRS BY IMPROPER MEANS OR ADJUSTMENT SUBJECT THEMSELVES AND OTHERS TO THE RISK OF SERIOUS OR FATAL INJURY 1 THE HEATING PRINCIPLE OF MICROWAVE Microwave is one kind of radio wave whose wavelength is very short frequency is very high Therefore it is called ultrahigh frequency electromagnetic wave Microwave can heat food mainly result in the mutual affect of the food in the microwave field and the microwave field itself Under the affect of microwave field the thermal effect mechanism produced from the mutual affect of the microwave and the food includes two aspects One is Dielectric loss of polar molecule the other is conductive 2 loss of ion Usually food is constituted of organism plant and animal The organism is formed by all kinds of polar water molecule polar protein molecule and all sorts of saltion The center of gravity of the positive and negative charge in the molecule is not coinciding In normal condition the molecule is in irregular order due to its thermal action thus the food do not appear polarity FIG 1 la Under the action of outer electric field the positive end of the polar molecule trend to the negative electric field the negat
18. SANYO ue Oven Range EM S1053 EM G2053 EM S1063 EM G2063 EM S1553 EM G2553 EM S1563 EM G2563 EM S3553 EM G4753 Service Manual nn ao cook veu gt eee E CCCA ceeoii Tooke INTRODUCTION This Microwave Oven Service Manual is printed in a loose leaf format Each part is divided into sections relating to a general group of components and each section is subdivided into various parts describing a particular component or service procedure The subdividing of the subject matter plus the loose leaf form will facilitate the updating of the manual as new or revised components and service procedures are introduced Each page of this service manual will be identified in the lower right hand corner and as new or revised pages are published it will be easy to keep the manual up to date by following the filing instructions on the cover letter This Service Manual is a valuable service tool and care should be taken to keep it up to date by prompt and proper filling of subsequent pages as they are issued CONTENTS SAFETY PRECAUTIONSE rte tn DR nn te Dire nt s rs nee ent l msn n nn res tne draibes 2 1 THE HEATING PRINCIPLE OF MICROWAVE inner REEE 2 THE STRUCTURE AND WORKING PRINCIPLE OF MICROWWAVE OVEN iii 4 2 1 HIGH VOLTAGE REGCTIFYING CIRCUIT roce aE AE A 4 2 2 MICROWAVE GENERATER 2 einen teen TEAREN AE ERRA S EARE EEEE AERE ARAD EARE 4 2 3 COOLING SYSTE
19. ade of an avometer the value should be about 3 4V FIG 5 5 If there is no voltage at all it indicates the transformer has broken and should be replaced by a new one If it is enough to 3 4V check the filament resistance of the magnetron measure the filament plug with the Rx1 grade of a avometer FIG 5 6 If it is open circuited it indicates the magnetron has broken and should be replaced by a new one It is normal if the resistance very small Then check whether the magnetron steel has broken if broken replace with a new magnetron If there is no problem with the magnetron check the high voltage diode then Measure the diode with Rx10K grade of an avometer the rod end of the avometer connect the cathode of the diode the rod end of the avometer connect the anode of the diode FIG5 7 The avometer reading should be about 150 thousand ohms The change the rod to different electrode the reading should be If the reading is very small and near to short circuit it indicates the high voltage diode has been punctured and should be replaced by a new one If the high voltage diode is OK then check the forwarding plug of the transformer to see whether it is enough to 230V If it is not enough check the micro switch of the time and power distributor Connect the two rods of the avometer to the 1 2 place of the timer with Rx1K grade It is normal if the reading is 0 when at cut off condi
20. an attention must be paid to prevent the cool wind from blowing directly to the glass part of the magnetron to avoid blasting 2 4 ELECTRIC CONTROL SYSTEM To those mechanical control microwave oven electric control system mainly composes of interlock switch timer power distributor and thermal cutout etc The electric control system of those tough control microwave oven is mainly composed of interlock switch computer en controller and thermal cutout etc 5 fuse main latch switch 2 4 1 DOOR INTERLOCK SWITCH Drawing 2 5 a is the circuit and construction diagram E pilot switch g of the door interlock switch of brand EMN 109 N microwave oven It mainly consists of latch switch S1 2 pilot switch S3 door hook and starting mechanism of the door interlock switch s door closed assistant latch switch a Fig 2 5 There fixed hooks on the oven door and opened two rectangle hole at the corresponding place at the right of the oven and the hook Inside each rectangle hole there fixed a micro switch When the oven door closed the two hook on it would insert into the rectangle hole and just push down several micro switches At that time S1 S2 are closed S3 is cut off and the microwave oven is under preparation of working To that mechanical control microwave oven no sooner you turn the time switch to set the heating time than the power would be supplied to the back to start the oven To those touch control microwav
21. ating food it is also one side of the cavity FIG 2 8 It is the most liable place where microwave leakage occurs Especially after a long time using the microwave leakage would enlarge at the hinge and the hook Anyway mechanic damage would also cause large amount of microwave leakage Therefore the main methods designed for preventing microwave leakage of the door are as follows 1 Assemble a layer of steel filament or a thin metal plate with many holes at the middle of the window to made it is possible to observe the heating as well as shielding the microwave 2 The widely used seal measurement at present is to assemble a current resistant construct between the door and the doorframe FIG2 9 is current resistant the typical construction fig of the door It was PIS eae designed according to the theory of ds 9 THETRANSFERING LINE ONE FOURTHWAVE N LENGTH IMPEDANCE CHANGER Although No xd there is no connecting point from a mechanical SSS N a point It is sealed at the seam from the point of front door plate LAC nn a electricity so it is called CURRENT RESISTANT sy oven door Fig 2 9 Recently with the installation of noise filter in the current resistant trough the effect to restrain the microwave leakage include high subharmonic have been much improved 3 TYPICAL CIRCUIT ANALYASIS OF MICROWAVE OVEN We have introduced the structure and the working principle of the microwave oven previousl
22. e heated matter Er Stands for relative dielectric constant of the heated matter 3 2 THE STRUCTURE AND WORKING PRINCIPLE OF MICROWWAVE OVEN Microwave oven can be classified to many kinds according to various construction volume and control function But anyhow the main electric parts are all 230V composed of high voltage rectification cooling system ci Microwave generator electric control system and heating chamber FIG 2 1 Its working process are as follows 230V power frequency voltage transferred to the rectifier through electric control system and then be changed to 4000V direct volt age by the rectifier and be then transferred to the microwave generator the generator stars working to transfer the microwave energy to the heating chamber for heating food through wave guide tube At the same time the electric control system set off the cooling system to cool the working rectifier and the microwave generator to keep the oven working steadily from a too high temperature If something wrong with the cooling system cause the temperature too high the control system would cut off the power automatically to prevent microwave generator being damaged form the high temperature Now we d like to introduce the working principle of each part of the widely used model mechanical control and touch control microwave oven 2 1 HIGH VOLTAGE RECTIFYING CIRCUIT At present home use microwave oven adopt this high voltage rec
23. e oven hardly do you set the heating time and power and touch the start button when the power would supplied to the back to start the oven When press down the door release button S1 S2 are cut off S3 is closed and the microwave oven would stop operating immediately Provided due to some man made or the appliance itself reasons when the door is open S1 S2 are closed due to the pilot switch S3 still at conducted condition would make the 230V voltage short circuited and fused the fuse and will never let the microwave oven working when the door is open From this we can understand the function of the interlock switch is when the door is unclosed the oven wouldn t work when the door is opened when the oven is working it would stop the working immediately FIG 2 5b Tea Screw 2 4 2 TIME AND POWER DISTRIBUTOR Time and power distributor is mainly composed of timer motor and two sets of gear switch S4 and S5 When latch switch door hook the timer is at zero position the gear switches are cut off when the heating time is settled the gear switch is closed When started the oven the time motor starts working When it reaches the settled time it would cut och transformer timer amp power motor off the gear switch s4 to step the oven working The gear switch S5 is designed for controlling the output of the microwave oven actually for controlling the output of the magnetron It mainly by the method which make
24. f a avometer If it is open circuited it indicates the turntable motor has broken and should be replaced by a new same model one If the resistance value is between 15 22 K it indicates the turntable motor is normal Then check the connecting shaft weave If the plastics which the shaft insert in has broken a new shaft weave should replace it 3 Repair when the oven can heat but the lamp is not on Pull out the power plug take down the cabinet an discharge the capacitor 19 Pull out the two terminal plugs of the lamp Measure the two plugs of the lamp with the Rx100 grade of a avometer If it is open circuited it indicates the lamp has broken and should be replaced by a same model one 4 Means of repair when the oven stop working after several minutes operating The phenomenon indicates the thermal cutout is playing its protective role and you should check whether the fan is working in normal Turn off the oven pull out the power plug take down the cabinet discharge the capacitor then turn the fan with hand to see whether it is moving flexibly If not it indicates that the oil bearing of the fan motor has run off the oil and should take down the fan combination to repair the motor Loosen the two screws which fix the bearing out the shaft and the bearing and rinse them with kerosene ATTENTION The bearing can only be wiped with a silk which moistened with kerosene rather than be washed in the kerosene because there are
25. he magnetron to control the power input At normal condition the thermal cutout is always conducted FIG 2 8 When something wrong with the cooling system that cause some abnormal conditions such as molding or thermal breakdown which made the temperature of the magnetron reach the limit value Then the thermal cutout would work to turn off the power to prevent the magnetron from being damaged 2 4 4 HEATING CHAMBER Heating chamber is the place where the microwave and the food affect mutually There are lots kinds of chamber Accord ing to the working characters it can be classified to carton type cavity type radiation type slow type surface wave type etc The present adopt chamber for food cooking microwave oven is the typical carton type heating FIG 2 8 The heating chamber is mainly composed of oven door and oven cavity From the microwave theory it is a microwave resonant cavity that can contain many kinds of oscillating models simultaneously Microwave enters into the oven cavity through the wave guide and the coupling appliance and most of its energy is absorbed by the food after it is reflected in the cavity repeatedly those which haven t been absorbed will be reflect to the magnetron A good designed oven cavity should have a good impedance matching with the magnetron the energy should be less reflect and distribute evenly in the oven cavity improve the heating efficiency Generally at the same input power the larger the cavit
26. ive end of polar molecule trend to the positive electric field and somewhat arrange in order through the direction of the electric field FIG 1 1c This phenomenon usually is called TORQUE POLARITY When the outer electric field apply for the opposite polarity the polar molecule then arrange an opposite direction order accordingly FIG 1 1b If the direction of the outer electric field changed repeatedly the polar molecule would repeatedly sway accordingly During the swaying it is understanding that the polar molecule would produce heat due to somewhat similar friction among them When the electric field is applied for ultrahigh frequent microwave field from the outside its direction would change tens billion times per second so do the molecule This kind of molecule swaying producing similar frictional heat from the interference and block of the action strength among the molecule and changed to microscopic microwave heating Microwave heating not only concerned the nature of the matter itself but also closely connected with the electric strength and frequency When the frequency is low the molecule swaying rate and the acute degree of the mutual friction among the molecule is low and would produce much heat When the frequency is too high as the swing of the polar molecule is with rotating inertia it made the swing do not in line with the changing rhythm of the electric field because of the friction drag thus actually lowed the polar molec
27. ltage 4 between the cathode and anode of the magnetron a filament voltage to the cathode filament of the magnetron The working process of the magnetron When the anode volt age gradually rises from zero the anode current is approx zero the power is very small as well When the anode voltage rises to THRESHOLD voltage value the magnetron starts oscillating and the anode current would increase obviously provided the anode voltage rises a little more the anode current would increase a lot FIG 2 4 and would reach the rate value quickly If the anode voltage is undulating it would cause the anode current swing fiercely even made the magnetron stop oscillating For keeping a steady output the power supply circuit of the oven must supply a stead direct current voltage The filament voltage of the magnetron must be supplied by an alternating current voltage For simplifying the circuit it would be supplied by the same leakage magnetic transformer with the anode power high voltage power The filament of the magnetron which the present used microwave ovens are all treated through some special technology and all have the cold start character But when in cold start there still is a very strong surge electric field attached to the surface of the anode and would be harmful to the anode In order to reduce the surge voltage the filament of the magnetron must be connected as the FIG 2 3 shown In this figure when the anode current of
28. microwave oven may occur compound breakdown due to all kinds of different reasons thus when overhaul they all should be taken into consideration Special attention must be given to the microwave leakage and the electric insulation when examine because they may do harmful to the repairing staff 5 1 EXAMINING THE BREAKDOWN CAUSES How to examine a microwave oven with breakdown A better means which demonstrated in practical operating 15 are through inspecting and listening On the basis of large amounts of perceptual knowledge you can judge and analysie the break down quickly and correctly 5 1 1 INSPECTION Inspect whether the oven shape is disordered and where is the disordered position If any It is normal if the cabinet disordered a little but abnormal if the oven the door disordered the door hook broken the door crooked or there are too much looseness between the door and the oven after the door is closed 5 1 2 LISTENING Listening to the sound of the oven operating and the noise of the fan Minor wen wen noise cycling kala noise and shishi noise should be considered as normal But it is abnormal if the following noises occur 1 Sound wen wen noise 2 Long time shishi noise 3 Strike sound like Pipa pipa 5 2 SPOT EXAMINING STEPS OF THE MICROWAVE OVEN 5 2 1 EXAMINE THE MICROWAVE INSULATING RESISTANCE Measure the insulating resistance with a avometer or a megaohmmeter the val
29. oven Then measure again part at the leakage amount should be less than 1 milliwatt cm2 right above V af Generally it should be controlled below 0 75 milliwatt cm2 with some allowance micro switch If the leakage occurred at the right door crack adjust the screws which fix the interlock holder and the hook If the leakage is the larger side at the right above of the oven then adjust the upper screw as FIG 5 15 Loosen out the screw door pushing push the door close to the oven to hook the door hook with the part at plastic parts then tighten the Screw again If the leakage is right below larger at the right below then adjust the lower screw as FIG 5 Fig 5 15 15 Loosen the screw push the door close to the oven to hook the door hook with the switch holder tightly then tighten the screw again and open and close the door repeatedly to check whether the door can operate flexibly whether the hook and the switch are in their normal position If it is not in position then adjust the door hook and the switch holder repeatedly to make them to normal position to put through the interlocks to cut off the pilot switch to less the loose between the door and the oven then measure the leakage with microwave measure again If the leakage still exceeds standard requirement then inspect whether the right oven is even or not if not smooth it Then adjust the door and the oven to eliminate their loose to the ultimate
30. ow and the air vent at four sides of the oven with the probe of the measure When measure the moving speed of the probe should not exceed 25mm per second and the measuring direction should be the same with the outing direction of the probe should not exceed 25mm per second and the measuring direction should be the same with the outing direction of the microwave leakage FIG 5 2 Fig 5 3 When measuring the ultimate value of microwave leakage of all the measure position should not exceed 1 milliwatt cm2 of should be considered as abnormal 5 2 4 EXAMINE WHEN THE OVEN AT OPERATING BUT THE FOOD CAN T BE HEATED 16 1 Examine when the lamp is on the glass tray is cycling the fan operating in normal Take off the cabinet starting the oven measure the plug of the transformer with an avometer to see whether it is enough to 230V If it is enough to 230V then the secondary high voltage of the transformer should be examined as FIG 5 3 Measure it with the 2500V alternating grade of model 500 avometer One rod of the avometer connects the iron core of the transformer the other rod connects the secondary high voltage plug FIG 5 4 The avometer reading should be about 2100V when measure be careful with the high voltage If no voltage at all it indicates that the transformer has broken and should be replaced by a new one If it is enough to 2100V then check the filament voltage of the transformer with alternating 10V gr
31. perature would rise high very quickly When the temperature reached the working point of the thermal cutout S6 S6 will be cut off immediately to cut off the power supply to the magnetron and the magnetron will stops working right away The PC board is cut off to prevent the magnetron from being damaged by overheating When the thermal cutout is cut off the magnetron motors and the lamp would stop working simultaneously Moreover the thermal cutout has the self resuming character when the temperature lowered it will resume to close condition Circuit diagram of computer controlled microwave ovens Circuit diagram for mechanical controlled microwave ovens 4 1 4 HOWTO ASSEMBLE AND DISASSEMBLE MICROWAVE OVEN COMPONENTS In the following pages we will introduce the ways in which the various parts of a typical microwave oven can be disassembled and assembled THE CABINET To disassemble the cabinet Pull out the power plug Loosen the four screws at the back of the oven with a screwdriver FIG 4 1a Push the cabinet back 25mm according to the arrow direction shown at FIG 4 1 b and the cabinet can be taken off a a Fig 4 1 To assemble the cabinet 1 2 4 2 Put the cabinet on the oven and push it full ahead b Check whether the up right and left troughs have been inserted with the curved with the curved rim of the oven FIG 4 1 b If the cabinet and the oven are not tallied exactly then it
32. s broken and should replace it with a new same model one Fig 5 13 5 3 REPAIRING METHOD OF SEVERAL BREAKDOWN 1 Repair when there occurred large amounts microwave leakage There are many factors which may cause microwave leaking Following mentioned may be the main causes of microwave leakage 1 The door deformed the hinge loosed or damaged that KK caused the door can not close tightly A door hinge up 2 The door pressing cover or the embed piece damaged or come off door 3 Obvious damage or uneven of the oven 4 There are filth between the door and the oven door hinge low 18 5 The door and the oven are serious loosed after the door closed 6 The crack of the door shielding net cover Before repairing check whether the above listed point are existed if not can you start the microwave oven Place a graduate of about 275ml water at the middle of the glass tray close the door time set at 3 minutes power at high make the oven operating in normal Rectify the microwave leakage measure measure the amount of the microwave leakage around the oven with its probe If there are places which the leakage exceeds the standard requirement then repair them accordingly If the leakage amount exceeds 1 milliwatt cm2 at the left door crack then pull out the power plug take down the cabinet adjust the screws of the hinge up and low as figure5 14 to less door pushing Peery the gap between the door and the
33. should be reassembled or those untallied parts should be smoothed Tighten those four screws please make sure that one of the screws should have a plum blossom shape washer to keep a good earth THE DOOR COMBINATION To disassemble 1 2 3 Pull out the power plug Take off the cabinet Loosen the two six angle screws of left hinge up with a socket wrench FIG 4 2 Push the door release button to have the hook out FIG 4 3 Pull the hinge with the door out of the oven together and take off the washer of the hinge low shaft FIG 4 2 Pick up the ten inverse hooks which around the cover with a small screwdriver carefully ATTENTION the cover is made of plastics and is very liable to be broken and take six angle screw i g T oven NN p RO Hide 42 out the cover 7 Take off the two screws at the door side with a screwdriver 8 Take off the hinge up FIG 4 2 Lis 9 Apart the doorframe from the doorplate A a er atch switch hol der FIG 4 2 Ashen Maten ston 10 Take off the hook spring with a pointed S door hook lt plier then the hook combination Aot auton pilot switch 11 Clamp the window plate with hand push it down according to the arrow direction and take it off af DEO To assemble the door combination see sketch 4 2 to 4 5 Fig 4 3 1 Apply proper silicon grease or lubricating 4 3 Pull out the power plug grease on the mark of the hook fir
34. st then fix the hook on the oven door and the spring on its place FIG 4 5 check whether the hook is operating in normal Apply proper silicon grease or lubricating grease on the mark of the hinge UP install the hinge UP in the hole at right above of the door as FIG4 2 then install the window on the door as FIG 4 1 make sure the hook won t out Then tighten each hook on the window to the trough of the door After assembled check whether the door hook is working in normal Fig 4 4 Fig 4 5 Tear off the back protective paper of the window then the sides of adhesive tape as FIG 4 1 and stick it on the window Tear three right sides protective paper about 10mm and fix the window in the doorframe as FIG 4 1 Tear off the adhesive protective paper of the lining and stick it on the door as FIG4 1 slip the hook on the doorframe and fix the doorframe on the door tighten it with screws After assembled check whether the hook working in normal and whether the hinge UP is its position According to the FIG 4 4 shown paste the inner lining inside the doorframe make sure it is pasted smoothly and should have no air bubble Slip the washer in the hinge shaft then put the hinge shaft in the hinge hole on the bottom of the oven the hinge in the rectangle hole on the left above and hooked it with the door hook Place a 0 15mm thin paper between the door and the oven level the door and the oven
35. stment 0 ececeeeeeeeee teenie eter teneeeeeteeeeeeteeeeetnieeeentaa 21 7 COMMON BREAKDOWN OF MICROWAVE OVEN AND MEANS OF REPAIRING 21 SAFETY PRECAUTIONS PRECAUTIONS TO BE OBSERVED BEFORE AND DURING SERVICING TO AVOID POSSIBLE EXPOSURE TO EXCESSIVE MICROWAVE ENERGY A Do not operate or allow the oven to be operated with the door open B Make the following safety 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 generating compartments check the magnetron wave guide or transmission line and cavity for proper alignment integrity and connections D Any defective or misaligned 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 release to the owner F Operate the oven from a properly grounded AC outlet capable of supplying 230 volts THIS MANUAL AS WELL AS THE INFO
36. the magnetron circulates the filament current should flow to the FA end from the lower end n kV anode voltage anode current L mA Fig 2 4 2 3 COOLING SYSTEM In the working process of the microwave oven the magnetron often makes the anode temperature rise due to anode loss caused by the electronics strike the oven surface and the heat radiate of the cathode To prevent the anode temperature rise too high thus affect the working steady and its life span it is necessary to cool the magnetron According to the different models and rate output of the magnetron compelling wind cooling and flowing water cooling can be adopted Usually the home used microwave oven adopts the compelling wind cooling method and all are fixed with cooling fin Cooling system includes fan motor air duct air entrance air vent etc The flowing direction of the cooling wind should Be parallel to the cooling fin of the magnetron Generally we adopt the method of air blast rather than air absorb And all the cabinet of the oven is with air entrance and air vent the hot wind blowing through the magnetron is guided with air tube to improve the cooling effect In the technical parameter chart of the magnetron it usually will give out the requirement of cooling wind A shortage of cooling wind would damage the character of the magnetron even burn out the magnetron The amount that the fan blasted should not be less than the requirement When fix the f
37. tifying circuit as shown at diagram 2 2 The circuit is a single phase semi wave double voltage rectifying circuit The circuit has only a high voltage capacitor a high voltage diode a magnetic leakage transformer besides the magnetron is very simple The working principle of the circuit 230V power boosted through the transformer output about 2000V alternating high voltage current when the high voltage winding is at the positive half circle the high voltage winding is at the negative half circle the diode is cut off and the magnetron is conducted The electricity charged at the positive half circle of the capacitor is series connected with the positive phase of the winding voltage and got a doubled about 4000V direct high voltage then transferred to between the cathode and the anode of the magnetron Fig 2 2 Fig 2 3 a 2 2 MICROWAVE GENERATER Microwave generator is the heart of microwave oven The quality of a microwave oven mostly depends on the quality of the microwave generator A microwave generator is mainly composed of magnetron and its power supply circuit FIG 2 3 is the typical circuit diagram of the present used microwave oven s generator The power supply circuit is composed of rectifying circuit and filament circuit Usually we adopt continuous wave magnetron It can turn the direct energy which is applied to the magnetron after being high voltage rectified to microwave energy the power supply circuit supply a direct high vo
38. tion If the reading is it indicates the micro switch has broken and the timer should be replaced by a new one If all the above examination shows normal then check whether the terminal plug of the magnetron and the capacitor have loosened if it is loosened pinch it tightly with a pliers 5 2 5 EXAMINE THE STARTING AND THE 8A FUSE OF THE MICROWAVE OVEN Pull out the power plug take off the cabinet discharge the capacitor measure the resistance value of the primary winding and the secondary winding of the transformer with an avometer FIG 5 10 and FIG 5 9 The resistance value of the primary winding should be about 2 2 ohms the secondary winding should be about 130 ohms Otherwise it indicates the transformer has broken and should be replaced by a new one 17 transformer secondary winding TN Fig 5 4 filament wingding Fig 5 5 magnetron Fig 5 6 capacitor Se Adinda Fig 5 8 If the transformer is normal then the high voltage capacitor should be checked Pull out the connecting plug of the capacitor and measure it with Rx1 grade of an avometer the two rods of the avometer connect the two polarity of the capacitor When they just connected the reading of the avometer should be Zero then increases to nine megaohm slowly Change the rod to different polarity the reading repeat from zero to nine megaohm FIG 5 11 it means the capacitor is normal If the indicator of the
39. ttle more time beating it is normal 5 4 4 MICROWAVE DEFROST Place a graduate of about 200ml water on the turntable glass tray of the oven power set middle time set 4 minutes to make the oven operating in normal When the bell of the time ring open the door It would be normal if the water is lukewarm 20 6 1 6 CRITICAL PARTS SERVICING IMPORTANT THINGS TO DO PRIOR TO CRITICAL PARTS SERVICING The following instructions are CRITICAL to the owner s safety Be sure to follow all the instructions Contact the manufacturer or distributor if you have any question 1 1 2 3 6 2 1 If the oven is operative prior to servicing a Microwave Leakage Test a k a Microwave Emission Check should be performed prior to servicing the oven Refer to Section 7 3 Microwave Leakage Test For the detailed check procedures In the event that any microwave oven found to have microwave emission level in excess of 4 mW cm2 The following procedures should be followed Inform the distributor importer or manufacturer the finding Record it in the logbook as well Repair the unit at no cost to the owner Investigate the oven and ascertain the cause of the excessive leakage Hold the oven in your facility and instruct the owner not to use the unil until the oven has In the event that the oven operates with the door open The following procedures should be followed Tell the user not to operate the oven Hold the o
40. ue should not be less than 2 megaohms Otherwise part examination should be taken at once Such as checking whether the motor the thermal cutout the transformer or oe glass tray the capacitor are electricity leaking 5 2 2 EXAMINATION OF THE RESISTANCE VALUE OF THE MICROWAVE OVEN Close the door set the time the oven is at operating condition but the power plug haven t been plugged in measure the two feet L N of the power plug with Rx1 grade of an avometer the resistance value should be about 2 5 ohm If open circuit occurs then you must check whether the 8A fuse is broken the primary winding of the transformer is open circuit the thermal cutout is open circuit or not you must check whether the interlock device is put through or all the plugs are connected well If short circuit occurred or the resistance less than 1 5 ohms you should check whether the primary winding of the power transformer is short circuited or part short circuited Fig 5 1 4 ED aan 5 2 3 EXAMINATION OF MICROWAVE LEAKAGE m Measure the microwave leakage with a microwave leakage transformer measure Place a graduate of 275ml water at the middle of the primary winding glass tray of the oven FIG 5 1 Close the door power set AU high time set to 3 minutes press the starting button to operate i N C the oven After rectified the microwave leakage measure ND measure around the door crack those hole position of the wind
41. ule swaying speed The friction dragging degree is concerning about the magnelectric wave frequency polar molecule shape and the matter s sticky degree To different matter s molecule there is different special frequency zone Those absorbing microwave energy from this zone are most capable to turn microwave energy to heat energy a b c Fig 1 1 Apart from the above said action there is another action which is electric ion under the action of microwave field act fiercely accompanied with the acceleration of electric field The positive ion transfer to the negative polarity of the field while the negative ion does opposite Accompanying with the changing electric field the electric ion hanging accordingly During the transferring heat produced with the crash among the ion This kind of action takes the main effect to those microwaves heating of high salt molecule No matter it is the polar molecule swaying or the ion transferring they both are turning the microwave energy which the heating matter got from the microwave field to heat energy From the analysis of theory we can draw such a conclusion that the power which a unit of volume matter absorbed from the microwave field as the following formula Pa KE fErtgd Pa Stands for the power the heated matter adsorbed from the microwave field K Stands for a constant E Stands for the microwave frequency f Stands for the microwave frequency tgd Stands for loss angle tangent of th
42. ven in your facility until it is investigated and repaired Contact the manufacturer and CDRH FDA immediately INTERLOCK ASSEMBLY REPLACEMENT AND ADJUSTMENT If you suspect defective primary secondary or monitor interlock switches use your ommeter digital or analog type to check the electrical continuity Make sure the power cord is pulled out and the high voltage capacitor is discharged before the electrical continuity check Set the ohmmeter to Low Resistance range and connect both leads alligator clips to the switch terminals Open the door and notice the meter reading the primary or secondary interlock switch should show an infinite resistancc when the door is open Replace it when it is defective The monitor interlock should show a zero or near zero resistance when the door is open When the door is closed the readings will be opposite If the oven has been rendered inoperative due to the failure of the monitored safety primary and or secondary interlock s You should replace all of the monitored safety interlock switched and the monitor switch Refer to Chapter 4 Sections and X for how to remove and assemble the interlock and monitor switches Always refer to Section 0 4 for adequate wiring diagram Monitor interlock must always be installed Repeat Step 6 2 4 to check electrical continuity Perform required checks and tests as described in Chapter 7 before releasing the oven to the owner 7 COMMON
43. y We shall analyze the complete set circuit of the microwave oven link with the practical circuit at this chapter 230V Fig 4 1 Fig 3 1 is the practical circuit diagram of a brand microwave oven Its corresponding working conditions are as follows The door closed SW1 and SW2 turned on SW3 closed power control relay has no power R1 R2 is cut off When cooking touch the starting switch to power the timer and the power relay RY1 RY2 closed the power supply to the anode of the magnetron and the filament changing the power frequency electric energy to microwave energy the microwave energy then transferred to the heating chamber for food heating At the same time the lamp turned on the fan motor begins to cool the magnetron The turntable motor set off to drive the food around and making the food heated evenly The microcomputer begins reckon the time when it reached the sets time power relay are cut off the power of the lamp all the motor and the magnetron are cut off the food heating process ended During the heating if the door was opened the interlock S1 S2 will cut off S3 will close all the motors and the magnetron will also be cut off the lamp will turn on the oven stop heating immediately If heating need go on just push down the starting button and closed the door the oven will continue its working When something wrong with the fan motor or the air vent was blocked that breakdown the cooling system the magnetron tem
44. y the less the energy density a unit volume would have in the oven and the more energy on the inside wall of the cavity would lose thence it would certainly slow down the heating speed low the heating efficiency Moreover too big of the cavity would either waste the material or appears very heavy The material for cavity usually use non magnetic stainless steel or zinc plating steel and have no high requirements for the conducting rate The inside coating of the cavity requires beautiful in look durable when use should be resistant against damp heat acid and alkali it should also comply with the food health requirements Safety interlock switch Door window Air vent Roller Shaft Turntable supporter Glass tray NO afk WN Light touch control panel Fig 2 8 To improve the heating evenness there often fixed a turntable glass tray at the bottom of the cavity FIG 2 8 It is through changing the relative place of the microwave and the heating matter to improve the heating evenness The turntable tray is usually made of heat resistant glass the glass contains some dielectric loss it can somewhat protect the magnetron when the cavity loading less There often fixed a dust proof low loss and heat resistant dielectric cover such as mica sheet Sometimes an impedance matching metal stick was fixed near the coupling or in the wave guide The door is designed for inspecting taking and placing the he
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