Slide 85Slide 85
D Board SOS Detect Circuit Explanation
One of the multiple functions of IC701 (Power MICOM) is to detects abnormalities on the Power
Supply. Abnormalities in the P board are reported to IC9003 via the SOS4 input:
The SOS2_15V, SOS3_3V and SOS5_5V detect input lines of IC9003, monitor for missing voltage
or short circuit of the 15V, 3.3V and 5V inputs to the D board. The remaining SOS6 and SOS 7
inputs, monitor for abnormal operation of the SC and SS boards.
A defective D board may also be responsible for the 2, 3, 4, 5, 6, 7, 8, or 9 blinks of the power LED.
A defective component on the D board may supply the MPU (IC9003) an erroneous input that
causes the unit to shut down, with the power LED blinking a number of times.
Since the D board does not control the blinking pattern of the power LED, any detected SOS
condition must be reported to the A board MPU (IC1100). The alarm pin of IC9003 reports all SOS
detections to the A board MPU. The “ready” pin of IC9003 is an acknowledgement line that reports
the operational status of the D board to the A board MPU.
