Monitor Board - Ricoh FT7770 Service Manual

6. Monitor Board

The main board applies timing pulses to the monitor LEDs from CN202-A3, -
A2, and -B2. Each signal line has three segmented timing pulses referred to
as A, B and C.
B18, -B17, and -Al?. So, the voltage on either side of the LEDs is always
balanced, and the LEDs stay off.
When a jam occurs, the CPU turns on the appropriate LED(s) by dropping
the timing pulse 1 volt; from 15 volts to 14 volts at CN203-A18, B18, B17,
and A17.
The CPU chooses the correct LED(s) through pulse timing.
With no jam, the same signal is applied to CN203-A18, -
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April, '89