Invivo Millennia 3155A, Руководство по обслуживанию

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1-8
LED. As long as the battery is good, the /EARLY_WARN line will be HIGH, and transistor Q2 will
be ON. Hence, the LED shows YELLOW (RED plus GREEN). When the /EARLY_WARN line
goes low (active), transistor Q2 will turn OFF; because transistor Q3 is still ON, the LED will show
RED.
When the fail-safe circuit is energized (power fails with the front-panel switch still ON), transistor
Q8's gate is still high (the front-panel switch is still closed). Because gate U2C is now enabled (pin
8 is high), the high voltage from pin 10 is coupled into the base of transistor Q7, turning it on, and
causing the GREEN LED drive to be diverted into the RED LED. Diode D22 increases the voltage
across transistor Q7 to guarantee that all the current will be diverted into the RED LED. Note that
transistor Q8 is wired as a source-follower to keep its substrate diode from conducting when the
voltage on U2C pin 10 exceeds the base voltage of transistor Q7.
1.2.10 Recorder Power. (Please refer to 185C187, sheet 1). Transistor Q4 supplies recorder power
regulated by its base voltage of 12 volts.