3
The original CPU board in the 4120 NPU was part number 636-588 (386SX microprocessor).
Since then, there has been a replacement board, the 636-802 (486DX2 microprocessor). This
publication describes the procedure for a new upgrade. The new board is part number 636-995.
This manual focuses mostly on an upgrade from a 636-802 to a 636-995. There are also
instructions contained for upgrading from a 636-588 to a 636-995.
• If you are upgrading from a 636-802 to a 636-995, proceed with the instructions below and
disregard the section entitled “Upgrading from a 636-588 CPU Board” at the end of this
publication.
• If you will be upgrading from a 636-588 to a 636-995, see the section entitled “Upgrading
from a 636-588 CPU Board.”
1. Backup the network.
2. Insert a blank floppy diskette into the floppy drive.
3. From the DOS prompt, type “format a: /s” to make a system diskette.
4. Copy FDISK.EXE, FORMAT.COM, and SYS.COM from the DOS directory to your floppy
drive.
5. From the CMOS setup write down the hard drive’s settings, including the size, type, sectors,
etc.
6. Disconnect the panel’s batteries at the fuse.
7. Disconnect AC power at the breaker.
1. Remove the front cover on the chassis inside the main cabinet by removing the four T15 Torx
screws located at its corners.
2. Locate the CPU board within the chassis. It’s the vertically oriented board, second from the
left. Most of the ribbon cables in the case will be connected to it.
Figure 1. Contents of Chassis
Continued on next page
Preparing System for Upgrade
Introduction
Protect System
Settings
Label all Ribbon
Cables on the CPU
Card
Location of the CPU
Board within the
System Case
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