NN-GT370M 4 DESCRIPTION OF OPERATING SEQUENCE 4.1. Variable power cooking 4.3. Turbo defrost, Auto cook control When the Auto Control feature is selected and the [Start] pad is tapped: High Voltage Inverter Power Supply (U) controls output power 1. The digital programer circuit determines the power level and by the signal from Digital Programmer Circuit (DPC).
NN-GT370M 5 CAUTIONS TO BE OBSERVED WHEN TROUBLESHOOTING Unlike many other appliances, the microwave oven is a high voltage, high current device. It is free from danger in ordinary use, though extreme care should be taken during repair. CAUTION Servicemen should remove their watches and rings whenever working close to or replacing the magnetron.
NN-GT370M • High voltage transformer (Located on inverter (U)) WARNING There is high voltage present with high current capabilities • High voltage diodes (Located on inverter (U)) in the circuits of the primary and secondary windings, choke • High voltage capacitors (Located on inverter (U)) coil and heat sink of the inverter.
NN-GT370M 6 DISASSEMBLY AND PARTS REPLACEMENT PROCEDURE 6.1. Magnetron NOTE: After replacement of the magnetron,tighten mounting 1. Discharge the high voltage capacitor. screws properly, making sure there is no gap between 2. Remove 1 screw holding supporter on the magnetron.
NN-GT370M 6.3. Low voltage transformer 5. Separate D.P.C board from tabs on the escutcheon base and remove D.P.C board. and/or power relays (RY1) To replace membrane key board NOTE: 6. Remove 1 screw holding back plate and bracket on escutcheon base, then remove back plate and bracket.
NN-GT370M 6.4. Fan motor 6.5. Door assembly 1. Disconnect 2 lead wires from fan motor terminals. 1. Support the door, remove 2 screws holding hinge A. 2. Remove 3 screws holding orifice assy and detach the orifice assy from oven assy.
Page 14
NN-GT370M 5. Remove door key and door key spring from door E. 9. Tighten 2 mounting screws. 6. Replace other components. To re-install components: NOTE: After replacement of the defective component parts of the door, reassemble it properly and adjustment so as to prevent an excessive microwave leakage.
NN-GT370M 6.6. Turntable motor 6.7. Quartz heater 1. Remove the motor cover by breaking off at the 4 spots 1. Disconnect lead wires from both side of heater terminals. indicated by arrows with a cutter or the like. 2. Bend back 2 locking tabs on heater mounting plate A & B respectively.
NN-GT370M 6.8. H.V. Inverter Power Supply 6. Remove 2 screws holding H.V. inverter on the inverter bracket. 1. Disconnect 2 high voltage lead wires from magnetron filament terminals. 2. Unplug connector CN701 & CN702 from H.V. Inverter board. 3. Remove 1 screw holding grounding plate on the base.
NN-GT370M 7 COMPONENT TEST PROCEDURE 7.3. Magnetron WARNING 1. High voltage is present at the output terminals of the High Voltage Inverter (U) including aluminum heat sink during any cook cycle. Continuity checks can only indicate an open filament or a 2.
NN-GT370M 7.4. Inverter power supply (U) 5. Program oven at High power for 1 minute and press [Start] pad. DO NOT try to REPAIR H.V. Inverter power supply a. After approximately 3 seconds, oven stops operating. (U).Replace complete H.V. Inverter(U) Unit.
NN-GT370M 8 MEASUREMENTS AND ADJUSTMENTS 8.1. Adjustment of Primary latch 8.2. Measurement of microwave switch, Secondary latch output switch and Short switch. The output power of the magnetron can be determined by performing IEC standard test procedures. However, due to the 1.
NN-GT370M 9 TROUBLESHOOTING GUIDE DANGER: HIGH VOLTAGES 1. DO NOT RE-ADJUST PRESET CONTROL on the H.V.Inverter (U). It is very dangerous to repair or adjust without proper test equipment because this circuit generates very large current and high voltage. Operating a misaligned inverter circuit is dangerous.
Page 21
NN-GT370M SYMPTOM CAUSE CORRECTIONS 1. Oven is dead. 1. Open or loose lead wire harness Fuse is OK. 2. Open thermal cutout / thermistor Check thermal cutout is defective. No display and no operation at all. 3. Open low voltage transformer 4.
NN-GT370M 9.2. Troubleshooting of inverter circuit (U) and magnetron This oven is programmed with a self diagnostics failure code system which will help for troubleshooting. H95, H97, H98 and H99 are the provided failure codes to indicate magnetron and inverter circuit problem areas. This section explains failure codes of H95, H97, H98 and H99.
NN-GT370M 9.3. Trouble related to Digital Programmer Circuit SYMPTOM STEP CHECK RESULT CAUSE/CORRECTIONS No display when oven is first plugged Fuse pattern of D.P.C. Normal →Step2 Open Replace D.P.C. or Fuse Pattern Low voltage transforment (L.V.T.) Abnormal 0V L.V.T. secondary voltage →Step3...
NN-GT370M 9.4. Simple way of H.V. Inverter/magnetron troubleshooting Purpose: Simple way (3/23 seconds rule) of identifying whether it’s Magnetron, Inverter or others. Set-up: The unit under question is connected through the Ammeter as shown below. Procedure: Follow the matrix table below to identify the problem source.
NN-GT370M 9.6. H.V. Inverter main parts list (F606YM300BP) Ref. No. Part No. Part Name & Description Pcs/Set Remarks Q701 A691EM300BP IGBT Q702 IGBT C701 ECWF5184N300 FILM CAPACITOR C702 ECQE2505T869 FILM CAPACITOR C703 ECWF2395N632 FILM CAPACITOR DB701 B0FBBQ000007 RECTIFIER BRIDGE L701...
NN-GT370M 10.2. PARTS LIST NOTE: 1. When ordering replacement part(s), please use part number(s) shown in this part list. Do not use description of the part. 2. Important safety notice: Components identified by mark have special characteristics important for safety.
Page 28
NN-GT370M Ref. No. Part No. Part Name & Description Pcs/Set Remarks F692Y9W40ZP NOISE FILTER (U) F02395E20KN CORD CAUTION LABEL KTE,PTE...
NN-GT370M 10.3. DOOR ASSEMBLY Ref. No. Part No. Part Name & Description Pcs/Set Remarks F30189V00XP DOOR KEY A F302A9V00KXP DOOR A (U) F302K9V00XP DOOR E (U) F30215G10XN DOOR KEY SPRING F30859V00XP DOOR C F31459W00XP DOOR SCREEN A...