The voltage at Point A becomes the divided voltage of TH111 and R111//R112 (combined resistance of parallel-connected resistors R111 and R112.) In Normal mode, the resistance at TH111 is much higher than R111//R112, and Q111 is off. (Note that the resistance at TH111 becomes lower as the temperature increases.) If the solder temperature at IC81 increases abnormally, the temperature at TH111 (thermistor) mounted closest to the land of IC81 increases accordingly, and the resistance at TH111 decreases. When the temperature at TH111 reaches 90-110_C (varying according to conditions,) the voltage at Point (A) becomes high enough to turn Q111 on, and the level of the XPROTECT line becomes low. The microcomputer detects the XPROTECT level and shuts the power to the unit off.
B
If no fan is connected between FAN+ and FAN-, or when the fan cannot rotate because of a foreign object caught in the blades, current will not flow to R3657, and Q3652 and Q3651-1/2 (E, C, B) are turned off. Then Q3651-2/2 (E2, B2, C2) is turned on, and the level of XPROTECT becomes low. � The microcomputer detects the XPROTECT level and shuts the power to the unit off. When FAN+ and FAN- are short-circuited, the electric potential at Point A becomes higher than GND level by the addition of the values at D3656 and D3657. As this value is lower than that at D3658, Q3651 (E, C, B) is turned off, Q3651 (E2, B2, C2) is turned on, and the level of XPROTECT becomes low.
C
4 DC detection circuit of SP terminal
D
POWER Assy
C
VD+5
6CH AMP
+5V R3357 (R3457) 18k Q3605 R3358 (R3458) 18k + R3603 10k C3602 100/10 Q3604 Q3607 Q3606
E B C
R108 27k
D
XPROTECT
Front L ch (SW, SL) Front R ch (C, SR)
� In Normal mode, both Q3605 and Q3604 are off. (1) When positive (+) DC voltage is generated at the SP terminal When positive (+) DC voltage is generated at the L or R channel, and VB of Q3605 becomes higher than that at the operation point, Q3606 (E, C, B) is turned on, and the level of XPROTECT becomes low. � The microcomputer detects the XPROTECT level and shuts the power to the unit off. (2) When negative (-) DC voltage was generated at the SP terminal Q3604 is turned on, and XPROTECT is activated.
