Kyocera FS-1050 Service Manual - Page 80

Eraser lamp control circuit The CPU (U01) turns pin #23 (ERASERN) of U01 to H level, transistors (Q16 and Q14) turns on consequently, and the 24 V DC given at pin #1 of connector YC05 applies to the eraser lamps. The eraser lamps thus illuminate as the current flows through the eraser lamp, the pin #2 of connector YC05, resistors (R75/R76, and R77/R78), and the ground. Pin #27 (ERRDYN) of the CPU (U01) is wired to the crossing of resistors (R75/R26 and R77/R78) via resistor (R74). The U01 turns pin #23 (ERASERN) to H level and monitors the input level after one second. If the eraser lamp is normal, the current flowing through R74 also flows the zener diode (DZ01), making the voltage at pin #27 to be approximately 3.7 V. On the contrary, if the level at pin #27 (ERRDYN) is less than 1 V for more than 2 seconds, despite the U01 turns pin #23 (ERASERN) to H level and applying the 24 V DC to pin #1 of connector YC05, the U01 recognizes that the current is not flowing through the eraser lamp. The message "Call service 5300" is then displayed. Engine board CPU U01 P25/ASCK0 23 ERASERN Eraser lamp cotrol circuit 2 Q16 R69 3 1 GND 27 ERRDYN P16/ANI6 1 2 R74 DZ01 GND R75 R76 R77 R78 GND +24V R68 2 1 C33 3 Q14 YC05 1 2 3 Eraser lamp ERASPW ERASER PGND Figure 4-3-4 Eraser lamp control circuit 4-21 FS-1050