Service manual

Power System 4-7
Figure 4-3 shows the distribution of power thoughout the system drawer.
Opens in the circuit or the PCM signal POWER_FAULT_L or the SCM signal
RSM_DC_EN_L interrupt DC power applied to the system. The opens can be
caused by the On/Off button or the cover interlocks. The POWER_FAULT_L signal
is asserted by the PCM module if it detects a fault and the RSM_DC_EN_L is
controlled remotely.
A failure anywhere in the circuit will result in the removal of DC power. A potential
failure is the relay used on the SCM modules to control the RSM_DC_EN_L signal.
The 4100 and early 4000 system drawers have three cover interlocks: one for the
system bus card cage, one for the PCI card cage, and one for the power and system
fan area. Later 4000 system drawers have four cover interlocks; the fourth switch is
for the second PCI card cage.
To override the cover interlocks, find a suitable object to close the interlock circuit
at the location identified in Figure 4-3. The switch assembly that contains single
switches for all three covers is located where all three covers meet.