SOS Circuit Overview
6 Blinks SOS: 6 blinks of the power LED may also be obtained from pin 3 of IC9003, the
DRV_RESET input. The D board provides the 5V source needed to power the C boards. On the C2
board, the 5V is routed back to the D board via connector C20/C10, C11/D31 causing pin 3 of
IC9003 to be high. If 5V is not routed back to the D board, pin 3 of IC9003 goes low. The set goes
into shutdown mode and the power LED emits 6 blinks.
7 Blinks SOS: Pin 93 of the MPU IC9003 monitors the status of the SC, SU, SD board. During
normal operation, the photo-coupler PC6480 outputs a low to pin 93. If the SC, SU, or SD board
becomes defective, a high is provided to pin 93. As a result, the unit shuts down and the power LED
blinks 7 times.
8 Blinks SOS: Pin 91 of the MPU IC9003 monitors the status of the SS board. During normal
operation, pin 8 of connector SS23 outputs a low to pin 91. If the SS board becomes defective, a
high is provided to pin 91. As a result, the unit shuts down and the power LED blinks 8 times.
10 Blinks SOS: The SUB5V and DT9V sources created on the A board are monitored by IC1100. If
they are not present at pin 30 and 34, the MPU shuts down the unit. The power LED blinks 10 times.
10 Blinks SOS: The F_STB_15V of the P board, as well as the derived SUB5V and DT9V sources
are monitored on the A board for excessive current. If a short circuit is developed in one of the
supplied lines, pin 114 of IC1100 receives a high. The SUB5V and DT9V lines are also monitored for
excessive voltage. When an over-voltage condition is detected, a high is also output to pin 114 of
IC1100. The DT9V is provided to a DC/DC converter to create the BT30V for the tuner. If the BT30V
becomes excessive, a high is output to pin 114 of IC1100. A high at pin 114 of IC1100 causes the
unit to shutdown and the power LED to blink 10 times.
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