Replacing the CPU Switcher Card
Introduction
The CPU switcher card is used in redundant master controller configurations to automatically switch the communications bus and city circuit from
a primary CPU card to a backup (secondary) CPU card when a trouble is detected by the 24-point I/O card. The CPU switcher card is located in the
Primary CPU Bay, the top bay in the back box.
The card layout within the Primary CPU Bay is different than that of a normal CPU bay. The CPU motherboard and daughter card, for instance, are
installed at the far left of the bay, rather than the right. Also, the network card slot on the CPU motherboard must not be used in redundant master
controller configurations. Immediately to the right of the primary CPU motherboard is the CPU Switcher Card and then the 24-point I/O card. Figure 1
shows a sample layout of a Primary CPU bay within a 4100U configured with a redundant master controller.
Removing the switcher card involves removing system power, detaching the two connectors from the card (at P3 and P4), and removing the four Torx
screws that fasten the board to the standoffs at the rear of the bay. However, because the switcher card is mounted in between other cards in the bay,
the CPU motherboard must also be removed to make it possible for the switcher card to be disconnected from the adjacent cards.
Figure 1: Primary CPU Bay Layout
Remove Power and Access the Primary CPU Bay
1. Disconnect any connection to the batteries at the PDM and then remove the power to the system at the breaker.
2. Lower the front door to the Primary CPU Bay (the top bay in a redundant master controller configured panel). Refer to Figure 1 for the
location of the CPU switcher card and CPU motherboard within the bay.
Remove the CPU Motherboard
The CPU motherboard must be removed from the bay before the CPU switcher card can be removed. Follow the steps below to remove the CPU
motherboard from the Primary CPU Bay.
1. Label and detach the service port and front display ribbon cables from the CPU daughter card, which is mounted to the CPU motherboard.
The service port cable is the thinner of the two ribbon cables.
2. Release and lower the card stabilizer at the front of the bay by pressing in the tabs at either end of the stabilizer. The card stabilizer must be
lowered before cards can be removed.
3. Pull the CPU daughter card out of its slot on the CPU motherboard and set it aside.
The next few steps involve the labeling and removal of cables connected to the CPU motherboard. You will be reattaching these cables later.
The locations and suggested labels of the connections are shown in Figure 2.
4. Label and disconnect any plug connected to P1 on the CPU motherboard.
5. Label and disconnect any plugs connected to P4, P5, or P6.
6. Label and disconnect any plugs connected to P7 and P8.
7. Label and disconnect any wires connected to TB3. Include as part of the label the name of the terminal block and the specific terminal the
wire connects to.
8. Label and disconnect any wires connected to the eight-position terminal block. Include as part of the label the name of the terminal block
and the specific terminal the wire connects to.
Note:
TB2, the RUI terminal on the CPU motherboard, is not used in redundant master controller configurations. Instead, use 567-217 RUI.
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579-272 Rev. C
CPU Switcher Card and Class B Motherboard Replacement Instructions
