8-1
CHAPTER
8
Major Subassemblies
This chapter describes how to remove and replace the system unit’s major
subassemblies.
■ Section 8.1 “Power Supply”
■ Section 8.2 “Speaker/Power LED Assembly”
■ Section 8.3 “System I/O Board”
8.1 Power Supply
The power supply is a self-contained metal assembly in the system unit top just
behind the disk drive mounting bracket (see
FIGURE 9-12).
The power supply is held in place by four hooks in the unit top that mate with four
slots in the power supply. In addition, the screw at the rear of the system unit that
holds the top and bottom halves of the unit together also retains the power supply.
The power supply wiring harness branches into four separate “power cables.” A 12-
pin power cable connects to the main logic board in its right front corner (see
FIGURE 9-13). Nearby, a 3-pin cable provides the keyboard soft power-on signal from
the main logic board to the power supply. Two 4-pin power cables supply power to
the hard disk drive and diskette drive (if present).
The power supply is auto-sensing and will operate with input voltage of 100-120 Vac
or 200-240 Vac without adjustment. If the power supply fails to operate, replace it.
FIGURE 8-1 shows how to remove and replace the power supply.
8.1.1 Removing the Power Supply
To remove the power supply:
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