31
Fig 4-1 Magnetron appearance
Fault type:
filament cathode open circuit, antenna spark, magnet flaws.
Caused faults: no microwave, lower microwave efficience, blown fuse and HV diode.
4-2 Infrared sensor
Type: OPTCSMLT15
Temperature range: 0~350
℃
Output: 0~3.5V
Ratio: 15:1
Scale: 1
℃
\10mV
Wiring define:
4-3 Pressure sensor
Range: 0~5Mpa
Output: 0~5V
Scale: 1atm / 50mV
Filament cathode
32
TOPEX service manual
5. Fault cause analysis
5-1 No microwave generated
Maintenance engineer should confirm the fuses are not blown. If the fuse blown continually when start
microwave, the problem must be caused by short circuit hidden in HV components, such as thyristor, HV
capacitor,HV transformers and so on. Measuring method refer to chapter 4.
If HV components have good quality, the possible reasons are terminals spark.
Confirm related thyristor has input or output voltage. If no input voltage, the problem may caused by the
former components described on wiring diagram, and if no output voltage, the problem maybe caused by
thyristor error.
If the problem is still encounter, change the magnetron and have a try.
5-2 Garble microwave power match
Thyristor can not control its output voltage may cause this fault, there are three cause reasons.
(1) Power control signal afford by main control board is error.
(2) Thyristor is broken.
(3) Mutual inductor is broken.
5-3 Infrared display value error
Infrared temperature is compensated, so the real temperature is lower than reading value displayed on
screen, but they are both have a certain proportion relation.
Measuring the output signal, if the signal is too large or stable, this problem must be caused by fault main
control board.
If the signal does not up while the temperature go up, the IR sensor may be broken.
5-4 Pressure display value error
Observe the pressure value displayed on screen whether change or not to affirm fault through press the
sensitive terminal by thumb.
Measuring the output signal between blue and white, if the signal can match the displayed value, the
problem maybe caused by pressure sensor.
If there is no output signal or weak signal change, that’s probably the pressure sensor error.
Replace the pressure sensor after the fault confirmed to avoid difficult installation.
5-5 Other components faults
Other components work mechanism are relatively simple,right work voltage and good quality, these
problems can be easily deal with according to the wiring diagram.