| 摘要 |
PROBLEM TO BE SOLVED: To detect a fault of light emitting diodes D1 of a LED display device using many light emitting diodes of a display panel of a communication controller. SOLUTION: A series circuit of a light emitting part of a photo coupler 21 and a second switching transistor Tr2 is provided between the cathode of the light emitting diode D1 of a lighting circuit 1 and a ground GND2. A Tr1 is turned off and the Tr2 is turned on to monitor the light reception output of the photo coupler 21 by a detection circuit 23. If the light emitting diode D1 is normal and is lit, the next LED is checked successively; but if it is not lit because of a fault, an alarm tone is emitted from a speaker 5, and the position of the defective LED is displayed on a display part 4. |
