Sharp R-21HT - Commercial Microwave Oven Service Manual Download Page 7

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Microwave Technologies Quiz

7. When working on a microwave oven with the cabinet removed, the

technician is exposed to a lethal danger. What is the danger?
a. The high voltage and current potentials even when power is

removed.
b. Radiation energy.

c. The high electrical resistance within the electrical circuits even

when power is removed.
d. The high wattage output from the magnetron.

8. When working on a microwave after disconnecting the power cord from

the outlet and removing the cabinet, the technician must:
a.  discharge the high voltage capacitor
b.  check the magnetron.
c.  check the fuse.
d.  check the door for RF leakage.

Summary of Contents for R-21HT - Commercial Microwave Oven

Page 1: ...Sharp Electronics Corporation Servicing Commercial Microwave Ovens R21JC 21HT R22GTF R22JT ...

Page 2: ...Len Hahn Senior Manager Field Services Support These ovens should not be adjusted or repaired by anyone except properly qualified service personnel ...

Page 3: ...T Commercial Microwave Oven All disassembly and testing procedures refer to the R22JT only While most heavy duty ovens are quite similar please refer to the specific model you are working on Your have information on all four models R21 series and R22 series ...

Page 4: ...rgy a Energy created by nuclear radiation b Energy created by chemical reaction c Energy created by electromagnetic generation d Energy created by atomic fusion 2 What is the frequency at which the magnetron operates a 60 Hz b 60KHz c 2450KHz d 2450MHz ...

Page 5: ...ometimes appear to cool faster when cooked in a microwave than when cooked in a conventional oven a Microwave energy does not last as long in certain foods and allows heat to escape b Because microwave ovens cook faster the food load cools faster c Microwave cooking utensils do not get hot so they draw heat from the food d Microwave energy is not as powerful as gas or electric heat energy ...

Page 6: ...llows the food to cool before eating c Allows the cooking container to cool before handling d Allows the food to finish cooking 6 When can metal be used inside a microwave oven a When you want the food not to over cook b When you want to generate more heat c When you want to protect your oven from cooking splatters d Never use metal in a microwave oven ...

Page 7: ...ower is removed b Radiation energy c The high electrical resistance within the electrical circuits even when power is removed d The high wattage output from the magnetron 8 When working on a microwave after disconnecting the power cord from the outlet and removing the cabinet the technician must a discharge the high voltage capacitor b check the magnetron c check the fuse d check the door for RF l...

Page 8: ...headaches c Only if the door or door switches are repaired d Only if the magnetron is replaced 10 To comply with the law what is the maximum amount of leakage allowed to be emitted from a microwave oven a 1 milliwatt per square centimeter b 3 milliwatt per square centimeter c 5 milliwatt per square centimeter d 7 milliwatt per square centimeter ...

Page 9: ...R 21JCA Control Panel 1000 Watts ...

Page 10: ...R 21JCA Oven diagram Rotary antenna Ceramic shelf Air intake openings Air ventilation cover and openings ...

Page 11: ...R 21JCA Ceramic Shelf Removal Using a putty knife lift up from underneath the ceramic shelf to remove shelf from cavity Be careful not to damage the rubber fins Rubber fins No rubber fin ...

Page 12: ...er fins No rubber fin Position the front of the shelf with the front of the oven The front edge of the shelf does not have a rubber fin Push down on the rear of the shelf to complete the installation taking care not to damage the rubber fins ...

Page 13: ...R 21JCA Schematic ...

Page 14: ...s that are used in microwave ovens are the step up type The 22JT employs two 1 20 step up transformer which outputs 20 volts for every volt applied to the primary When we apply 120 volts to the HV transformer primary 2400 volts will be available at the secondary Primary Secondary Input 120 volts Output 2400 volts ...

Page 15: ...nsformer will be 20x less than the current on the primary The high voltage doubler circuit will double the transformer secondary voltage to 4800 volts with an output current between 300ma and 450ma This 2400volt potential at 300ma is enough to kill you if came into contact with it Primary Secondary Input 8 amps Output 400 ma ...

Page 16: ...Danger ...

Page 17: ...Electrocution ...

Page 18: ...R 21JCA Single Magnetron ...

Page 19: ...High Voltage Doubler Operation ...

Page 20: ...High Voltage Doubler Operation Doubler charging Doubler Discharging Voltage Adding ...

Page 21: ...Magnetron Operation wave antenna Resonant Cavity Anode Cathode Heater Magnet around resonant cavity not shown ...

Page 22: ...Interior of Magnetron ...

Page 23: ...en Check magnetron venting and timer operation This unit is susceptible to get set to run without food load 2 Oven temp fuse open Check for proper venting for oven 3 Monitor fuse open Check primary and cook relay replace monitor fuse and secondary switch ...

Page 24: ...R 21JCA Schematic ...

Page 25: ...R 22JT Schematic 1200 Watts ...

Page 26: ...R22 25JT Disassembly Procedures Units can be stacked for some restaurant applications In this case the units need to be separated by removing the fixing angle before servicing ...

Page 27: ...CRITICAL SAFTEY WARNING WARNING You can be seriously INJURED or KILLED from the High Voltage circuit inside the Microwave Oven Disconnect AC Power and discharge the HV circuit before servicing ...

Page 28: ...Outer Case Cabinet Removal Disconnect AC power before Cabinet removal this will give the HV Doubler Circuit time to Discharge ...

Page 29: ...Outer Case Cabinet Removal Remove 2 screws on each side Remove 7 screws which are placed around the perimeter of the cabinet ...

Page 30: ...Outer Case Cabinet Removal Tilt the cabinet upwards to release and lift away You now have access to the HV circuit and control unit ...

Page 31: ...WARNING HIGH VOLTAGE Using a screwdriver with an insulated handle short together the two terminals of each High Voltage Capacitor H V Capacitors Short terminals with screwdriver ...

Page 32: ...Rear Cabinet Removal Remove 8 screws Note These 2 screws are brass Machine thread Lift up the rear cabinet be careful not to break the AC Line connectors ...

Page 33: ...Rear Cabinet Removal You can gently lay down the rear cabinet on top of the unit or You can disconnect the 2 AC Line connectors and remove the 1 grounding screw to completely remove the rear cabinet ...

Page 34: ...Rear View Upper Magnetron 1 White connector Lower Magnetron 2 Blue connector Rear View ...

Page 35: ...Right Side View Power Transformer for Upper Magnetron Note White Connectors on Harness H V Capacitor for Upper Magnetron Blower Motor High Voltage Rectifier Ass y for Upper Magnetron Noise Filter ...

Page 36: ...No Case positive lock connectors ...

Page 37: ...Right Side View Latch Hook Ass y Power Transformer for Lower Magnetron Note Blue Connectors on Harness H V Capacitor for Lower Magnetron High Voltage Rectifier Ass y for Lower Magnetron Control Unit ...

Page 38: ...Control Panel Removal Remove the air intake filter Ass y Gently pull the locks straight out to remove filter ...

Page 39: ...Control Panel Removal Remove 2 screws Slide control panel down to release ...

Page 40: ...Control Panel Removal Mark down the position of all connectors on a piece of paper and remove all 9 connectors Be sure to connect the cables in their exact original positions on the new control board ...

Page 41: ...Control Panel Disassembly Key Unit Control Unit Front View Rear View Remove 5 screws ...

Page 42: ...Control Panel Disassembly Lift up on the lock of cable connector CN G to release the lock Gently pull up on the Key unit cable ...

Page 43: ...Control Panel Disassembly Control Unit Control Panel Frame with Key Unit ...

Page 44: ...Door Removal Remove 4 screws 2 screws per hinge These screws can be very tight you may need a pliers or wrench to loosen before using a screwdriver ...

Page 45: ...Door Removal Open door and carefully pull door straight out Door removed from unit ...

Page 46: ...Door Installation Install door and tighten screws on the upper and lower hinges Apply Gorilla glue and test for normal latch hook operation and leakage before glue dries adjust door if necessary ...

Page 47: ...Door Disassembly ...

Page 48: ...Lower Stirrer Motor Access Snip off Bend sharp edges with pliers Replace cover with screw ...

Page 49: ...R25JT Schematic 2100 Watts Voltage Switches ...

Page 50: ...select the input voltage between 208 and 230 volts since power sources vary Note The oven will display an EE4 or EE5 if the voltage switch is set incorrectly Always measure the line voltage before adjusting the voltage switch EE4 Voltage is too high EE5 Voltage is too low ...

Page 51: ...How to set Voltage Switches ...

Page 52: ...door latching failure The monitor switches will shunt across the AC line and open the main fuse if activated disabling the unit The monitor switches will open when the door is closed The monitor switch and the fuse are stocked together as replacement parts You must replace two kits 1 for each HV circuit when an open fuse is detected QSW MA085WRE0 ...

Page 53: ...condary interlock switch 1 Secondary interlock Switches each high voltage circuit has its own secondary interlock switch which is used to supply AC line voltage to each high voltage circuit The secondary interlock switches close when the door is shut ...

Page 54: ...nses if the door is open or closed In addition it is also used in the standby mode Standby mode operates the blower motor to cool the magnetrons when the door is opened The oven light operates too The blower runs for 60 seconds regardless even if the door is closed ...

Page 55: ...Control Panel Schematic Primary interlock relay 1 Primary interlock relay 2 Door switch Oven thermistor Magnetron thermistor Key unit Foil pattern ...

Page 56: ...Control Panel Primary interlock relays 1 2 apply AC line voltage to each power transformer which supplies the doubler circuits with 2400 volts for magnetron operation ...

Page 57: ...Control Panel Oven thermistor is located on the exhaust duct and is used to measure the exhaust air temperature Oven thermistor Exhaust duct ...

Page 58: ... Panel Magnetron thermistor is used to measure the air temperature around the upper magnetron which can cause the unit to shut down This also protects the lower magnetron from overheating Magnetron thermistor ...

Page 59: ...Control Panel The key unit is a matrix of switches that is used for selecting the cooking process ...

Page 60: ...Control Panel The very fine foil patterns acts as a fuse and will open under excessive current draw Foil patterns ...

Page 61: ...ng THE UNIT MUST REMAIN DISCONNECTED FROM AC POWER AT ALL TIMES UNLESS SPECIFIED Disconnect the primary coils of each power transformer and leave disconnected until all troubleshooting activities have been completed ...

Page 62: ...oise filter is employed to meet FCC regulations by not allowing the 2450Mhz RF energy to travel out of the unit via the AC power lines A faulty noise filter will cause a no power condition The 20 Amp fuse is also located on the noise filter ...

Page 63: ...Troubleshooting the Noise Filter N L Disconnect wires from noise filter before proceeding ...

Page 64: ...Troubleshooting the Noise Filter N W ...

Page 65: ...Troubleshooting the Noise Filter L R ...

Page 66: ...anel Dead Disconnect all wire harnesses except the AC input connector CN 4 and the door sensing switch connector CN B the door sensing switch will not effect a dead unit Disconnect the Key unit connector CN G Key unit CN B CN 4 ...

Page 67: ...l Panel Dead Measure 120 volts at pins 1 7 of CN4 If 120 volts is present proceed with foil pattern check If 120 volts is not available check the noise filter fuse and check the oven temperature fuse if required Pin 1 Pin 7 ...

Page 68: ...Troubleshooting Control Panel Open Foil Pattern Visually inspect varistor and check for burns ...

Page 69: ...Troubleshooting Control Panel Open Foil Pattern Using a VOM measure the coil resistance of the primary winding of the transformer Check for 270Ω 10 ...

Page 70: ...Troubleshooting Control Panel Open Foil Pattern a b J1 d c Check for open foil patterns points a and b on the PWB Foil Repair Procedure ...

Page 71: ...Troubleshooting Key Unit Disconnect all wire harnesses except the AC input connector CN 4 and the door sensing switch connector CN B Disconnect the Key unit connector CN G Key unit CNB CN4 ...

Page 72: ...Troubleshooting Key Unit Connect AC power cord to wall outlet and open the oven door The blower and oven light will turn on indicating that the control panel is OK however the key unit must be shorted ...

Page 73: ... Momentarily shunt across pins 7 10 of the key unit connector CN G If a beep is heard the key unit is defective If the control panel does not beep the control panel is defective DISCONNECT AC POWER CORD FROM WALL OUTLET 1 7 10 ...

Page 74: ...ook is activating the plunger of the door switch when the door is open Using a VOM measure across the door switch contacts and check for continuity when the door is closed Open the door and now check for an open circuit Door switch Note orange wire ...

Page 75: ...Disconnect all wire harnesses except the AC input connector CN 4 door sensing switch connector CN B and Key unit CN G CN G CN B CN 4 Troubleshooting the Primary Interlock Relays ...

Page 76: ...k Relays Connect AC power cord to wall outlet Start cook process and measure for continuity across primary interlock relays 1 and 2 Note EE3 will appear on display after 9 seconds DISCONNECT AC POWER CORD FROM WALL OUTLET Relay 1 Relay 2 ...

Page 77: ...R 21JCA Control Panel J 1 RY 2 Power transformer RY 1 Oven lamp stir motor fan motor ...

Page 78: ...R 21JCA Open Foil Pattern a b J1 d c Check for open patterns points a and b on the PWB Foil Repair Procedure ...

Page 79: ...bleshooting Using Fault Codes Please refer to the following fault code tables in the respective Service Manuals to further troubleshoot each model R22JT Page 11 R25JT Page 12 R21JCA Does not use fault codes ...

Page 80: ...R22JTF Error code reference ...

Page 81: ...R22JTF Error code ...

Page 82: ...R25JTF Error codes ...

Page 83: ... EE16 EE17 There is only 1 magnetron thermistor which is located on the upper magnetron If EE16 is displayed on the control panel the magnetron thermistor is open If EE17 is displayed the magnetron temperature is too high ...

Page 84: ...Magnetron Thermistor EE16 EE17 To check the magnetron thermistor disconnect the thermistor and measure with a VOM See chart below for normal resistance meter readings Magnetron thermistor connector ...

Page 85: ... EE6 EE7 If EE6 is displayed on the control panel the oven thermistor has failed If EE7 is displayed the exhaust air temperature is too high In this case you would need to check the filter and be sure that the units air rear vents are not blocked ...

Page 86: ...Oven thermistor Exhaust duct To check the oven thermistor disconnect the thermistor and measure with a VOM See chart below for normal resistance meter readings Oven Thermistor EE6 EE7 ...

Page 87: ...Dual Magnetron Operation Common output of noise filter 120V Hot output of noise filter via primary interlock relays 1 2 Power transformers are wired 180º out of phase ...

Page 88: ...High Voltage Doubler Operation While the upper high voltage circuit is supplying power the magnetron the lower high voltage circuit is charging ...

Page 89: ...anel latch hook ass y and secondary interlock switches can cause the following error codes These error codes usually display within 9 to 13 seconds from when the cook cycle has started EE1 magnetron 1 failure EE2 magnetron 2 failure EE3 magnetron 1 and 2 failure Refer to page 11 in R22JT service manual for complete troubleshooting chart ...

Page 90: ...Troubleshooting EE1 and EE2 Troubleshooting techniques for fault codes EE1 and EE2 are common for each ...

Page 91: ...t you are checking the correct section relating to magnetron circuits and control section Note EE1 EE2 or EE3 usually does not necessarily indicate a defective magnetron so save yourself time and money by checking the associated parts as indicated in the following slides ...

Page 92: ...om H V transformer and measure for 120v AC If 120 volts or AC line input voltage is measured at the primary would indicate that the problem would be strictly a H V or magnetron issue The control circuits would be operating normally with AC voltage present ...

Page 93: ...ting EE1 and EE2 3 If 120 volts or AC line input voltage is not measured at the primary the problem would be the control circuits which includes the control panel secondary interlock switches and latch hook ass y ...

Page 94: ...s a defective latch hook ass y since only one secondary interlock switch is activated Note Verify that the wires and connectors are tight and not burned This can be a cause for intermittent fault codes Defective latch hook ass y Only 1 secondary switch is activated which is causing the EE1 fault code to display ...

Page 95: ...ok appears to be functioning normally check for continuity across the switches 6 Measure for continuity across each switch with the oven door closed This can be accomplished in circuit with unit unplugged from AC power zero ohms across each switch ...

Page 96: ... measure for continuity across primary interlock relays 1 and 2 Note EE3 will appear on display after 9 seconds Replace control PWB if there is no continuity at any of the 2 relays Relay 1 Relay 2 Troubleshooting EE1 and EE2 7 Check the primary interlock relays ...

Page 97: ...former then the problem is most likely to be a defective H V circuit or defective magnetron Please follow the next few slides on how to troubleshoot the H V section and magnetron Fault code EE3 would indicate the 2 H V circuits and magnetrons may be at fault This is highly unlikely so the problem will most likely be a defective latch hook ass y or control panel ...

Page 98: ...Troubleshooting the Power Transformers Disconnect primary winding and measure less then 1 Ω with an ohm meter ...

Page 99: ...Troubleshooting the Power Transformers Disconnect secondary winding and measure approximately 106Ω ...

Page 100: ...Troubleshooting the Power Transformers Disconnect filament winding between H V capacitor and magnetron measure less than 1Ω ...

Page 101: ...Remove grounding screw and check rectifier With meter set at X1000 you should get a high resistance in one direction forward bias Troubleshooting the H V Doubler Diode ...

Page 102: ...Reverse the leads of the ohm meter and you should read infinity reverse bias Note Loose H V lugs wires can cause intermittent or no high voltage Troubleshooting the H V Doubler Diode ...

Page 103: ......

Page 104: ......

Page 105: ...bler Capacitor Remove one lead from the Capacitor and put the meter leads onto the capacitor terminals You will see a momentary resistance reading and the meter will go back to infinity Reverse the leads and you will see the same ...

Page 106: ...Troubleshooting the Magnetron Remove the leads from the magnetron and read the filament resistance It should be less than one Ohm ...

Page 107: ...Troubleshooting the Magnetron Check to ensure you do not have a cathode to anode short You should read infinity between the terminals and the case of the magnetron ...

Page 108: ...Microwave Output Power Test ...

Page 109: ...Sharp Electronics Corporation This concludes our commercial microwave training ...

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