Service manual

System Overview 1-75
Figure 1–33 shows a simple block diagram of the B4186-Ax distribution board
and the layout for both distribution boards. These boards are used in systems
that have two QBBs. In systems with more than two QBBs, the hierarchical
switch actively performs this switching function.
The B4186-Ax module, used with the system box, is an active module because of
the CSB connection. The B4185-Ax, used in GS80 systems, does not have a
CSB connection and is completely passive.
There are five connectors on the B4186-Ax module, one is for the CSB bus cable,
two are for cables connected to the global port in QBB0, and two are for cables
connected to the global port in QBB1. There are four connectors on the B4185-
AA module, two are for cables connected to the global port in QBB0, and two are
for cables connected to the global port in QBB1.
The B4186-Ax is located in a distribution box housing at the rear of the system.
The B4185-Ax, located at the rear of a two-drawer system, is enclosed in its own
EMI enclosure that is to the right of the fans in both drawers. When the B4185-
Ax is used, the two drawers are physically connected to each other.