Dell OptiPlex N User manual

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____________________
Information in this manual is subject to change without notice.
1997-1998 Dell Computer Corporation. All rights reserved.
Reproduction in any manner whatsoever without the written permission of Dell Computer Corporation is strictly forbidden.
Trademarks used in this text: Dell, the DELL logo, and OptiPlexare registered trademarks of Dell Computer Corporation; Intel and Pentium are registered trademarks
and MMX and EtherExpress are trademarks of Intel Corporation; MS-DOS is a registered trademark of Microsoft Corporation; IBM is a registered trademark of
International Business Machines Corporation; 3Com is a registered trademark of 3Com Corporation.
Other trademarks and trade names may be used in this document to refer to either the entities claiming the marks and names or their products. Dell Computer
Corporation disclaims any proprietary interest in trademarks and trade names other than its own.
February 1998 P/N 57646 Rev. A01

v
Contents
Chapter 1
System Overview. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1
System Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2
Expansion-Card Slot. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4
Hard-Disk Drive . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4
Enhanced Dual-Interface EIDE Subsystem . . . . . . . . . . . . . . . . . . . . . . . 1-4
Built-In Video Controller . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4
Optional Built-In NIC. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-5
Stand for Vertical Orientation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-5
Computer Service . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-6
Computer Power Supply. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-6
Pin Assignments for the DC Power Connectors. . . . . . . . . . . . . . . . . 1-7
DC Power Distribution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-8
System Board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-10
Main Memory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-11
System Board Jumpers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-11
Interrupt Assignments. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-13
DMA Channel Assignments. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-14
Technical Specifications. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-15
Chapter 2
Basic Troubleshooting . . . . . . . . . . . . . . . . . . . . . . . . . . 2-1
Initial User Contact. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-1
External Visual Inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-2
Observing the Boot Routine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-3
Server-Based Diagnostics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-4
Hard-Disk–Based Diagnostics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-5
Internal Visual Inspection. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-7

vi
Diskette-Based Diagnostics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-8
Connecting the External Diskette Drive. . . . . . . . . . . . . . . . . . . . . . . . . . 2-8
Running the Diskette-Based Diagnostics. . . . . . . . . . . . . . . . . . . . . . . . . 2-9
Getting Help. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-10
Chapter 3
Beep Codes and Error Messages . . . . . . . . . . . . . . . . . . 3-1
POST Beep Codes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-1
System Error Messages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-4
Chapter 4
Removing and Replacing Parts . . . . . . . . . . . . . . . . . . . 4-1
Recommended Tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-1
Precautionary Measures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-2
Stand for Vertical Orientation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-3
Computer Cover. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-4
Control Panel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-6
Hard-Disk Drive. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-7
System Power Supply. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-8
System Board Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-9
Expansion-Card Cage. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-10
Expansion Card . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-11
Riser Board. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-12
DIMMs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-13
Microprocessor/Heat Sink Assembly. . . . . . . . . . . . . . . . . . . . . . . . . . . 4-14
System Battery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-16
System Board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-17
Appendix A
System Setup Program . . . . . . . . . . . . . . . . . . . . . . . . . .A-1
System Setup Screens. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .A-2
Index
Figures
Figure 1-1. Computer Orientation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2
Figure 1-2. Front-Panel Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3
Figure 1-3. Internal View. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3

vii
Figure 1-4. Riser Board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4
Figure 1-5. NIC Connector on I/O Panel . . . . . . . . . . . . . . . . . . . . . . . . . . 1-5
Figure 1-6. DC Power Connector P1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-7
Figure 1-7. DC Power Connector P2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-7
Figure 1-8. DC Power Connector P3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-8
Figure 1-9. DC Power Cables. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-8
Figure 1-10. DC Power Distribution. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-9
Figure 1-11. System Board Components . . . . . . . . . . . . . . . . . . . . . . . . . . 1-10
Figure 1-12. System Board Jumpers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-11
Figure 2-1. External Diskette Drive . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-8
Figure 4-1. Optional Stand Removal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-3
Figure 4-2. Computer Cover Removal . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-4
Figure 4-3. Service Access Lock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-4
Figure 4-4. Control Panel Removal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-6
Figure 4-5. Hard-Disk Drive Removal . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-7
Figure 4-6. System Power-Supply Removal. . . . . . . . . . . . . . . . . . . . . . . . 4-8
Figure 4-7. System Board Components . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-9
Figure 4-8. Expansion-Card Cage Removal. . . . . . . . . . . . . . . . . . . . . . . 4-10
Figure 4-9. Expansion-Card Removal . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-11
Figure 4-10. Riser Board Removal. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-12
Figure 4-11. DIMM Removal. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-13
Figure 4-12. DIMM Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-13
Figure 4-13. Microprocessor Removal. . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-14
Figure 4-14. Microprocessor Securing-Clip Removal . . . . . . . . . . . . . . . . 4-15
Figure 4-15. System Battery Removal . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-16
Figure 4-16. System Board Removal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-17
Figure A-1. System Setup Screens . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .A-2
Figure A-2. Sample Device List Screen . . . . . . . . . . . . . . . . . . . . . . . . . . .A-6
Tables
Table 1-1. DC Voltage Ranges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-6
Table 1-2. System-Board Jumper Descriptions. . . . . . . . . . . . . . . . . . . . 1-12
Table 1-3. Interrupt Assignments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-13
Table 1-4. DREQ Line Assignments. . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-14
Table 1-5. Technical Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-15
Table 3-1. POST Beep Codes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-2
Table 3-2. System Error Messages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-5
Table A-1. System Setup Categories . . . . . . . . . . . . . . . . . . . . . . . . . . . . .A-3

R
ead This First
W
arnings, Cautions, and Notes
Throughout this manual, there may be blocks of text printed in bold type or in
italic type. These blocks are warnings, cautions, and notes, and they are used as
follows:
NOTE: A NOTE provides helpful information about using the computer system.
A prerequisite for using this manual to service Dell computer systems is a
basic knowledge of IBM®-compatible PCs and prior training in IBM-
compatible PC troubleshooting techniques. In addition to information
provided in this manual and the User’s Guide that came with the system, Dell
providesthe DiagnosticsandTroubleshootingGuidefortroubleshootingpro-
cedures and instructions on using the Dell diagnostics to test the computer
system.
WARNING: A WARNING indicates the potential for bodily harm and pro-
vides instructions for how to avoid the problem.
CAUTION: A CAUTION indicates either potential damage to hardware or
loss of data and provides instructions for how to avoid the problem.
viii

System Overview 1-1
Chapter 1
System Overview
T
he Dell®OptiPlex®N computers are high-speed, upgradable computers
designed for centrally managed network operation. These computers have a
small-footprint, locked chassis with no externally accessible drives.
The OptiPlex N computers use the Intel®Pentium®microprocessor with
MMX™technology. The microprocessor is installed in a type 7 ZIF socket,
allowing the computer to be upgraded when faster microprocessors become
available.
The Pentium microprocessor contains a built-in clock multiplier circuit, which
increases the internal operating frequency to a multiple of the system clock fre-
quency. The microprocessors for Dell OptiPlex N computers operate at a
frequency of 166 MHz, 200 MHz, or 233 MHz, derived from a system clock
frequency of 66 MHz.
These Dell computers incorporate the high-performance PCI expansion bus.
This bus is built into the system board, which also integrates the micro-
processor, memory controller, hard-disk drive controller, video controller, and
other elements of the basic computer.

1-2 Dell OptiPlex N Systems Service Manual
S
ystem Features
In addition to the standard features found in a traditional personal computer, the
Dell OptiPlex N computers include the following new and/or advanced
features:
•One PCI expansion-card slot on a riser board
•One EIDE hard-disk drive
•Ultra DMA/33 EIDE interface for hard-disk drive transfer rates of up to
33 MB/sec
•Support for connecting an external diskette drive for troubleshooting
purposes
•Integrated cache memory controller that supports 512 KB of external
pipelined-burst cache memory
•Main system memory consisting of 16 to 256 MB of high-speed EDO
DIMMs
•Built-in SVGA controller attached to the PCI bus with 2 MB of video
memory
•Optional integrated 10/100-Mbps Ethernet NIC
•Optional NIC expansion card providing Wakeup On LAN capability
•Integrated Universal Serial Bus (USB) controller with two USB-compliant
connectors
•SMART-compliant hard-disk drive and SMART support in the system
BIOS, which provides notification at system start-up if the hard-disk drive
has become unreliable
•Server-based, hard-disk–based, and diskette-based diagnostics capabilities
For a complete list of system features, see “Technical Specifications” found
later in this chapter.
When following the text in this manual, assume that the location or direction
relative to the computer is as shown in Figure 1-1.
Figure 1-1. Computer Orientation
left
side
front
right
side
back

System Overview 1-3
Figures 1-2 and 1-3 show the system’s front-panel features and internal features,
respectively.
Figure 1-2. Front-Panel Features
Figure 1-3. Internal View
hard-disk drive
access indicator
power button
power indicator
serial port 1
connector
power supply
AC power
receptacle
expansion-card
cage
USB connectors (2)
keyboard connector
video connector
expansion-card slot
hard-disk drive
NIC connector (optional)
EIDE cable
parallel port
connector
mouse connector
serial port 2 connector
padlock ring
security cable slot
security access lock
DC power cable

1-4 Dell OptiPlex N Systems Service Manual
Expansion-Card Slot
The computer has one PCI expansion-card connector on the riser board (see
Figure 1-4). The computer automatically assigns any required memory space,
IRQ lines, and DMA channels to an installed PCI expansion card during system
start-up. The Wakeup On LAN power connector on the riser board supports an
optional NIC expansion card with Wakeup On LAN capability. The power LED
illuminates when DC power is applied to the riser board.
Figure 1-4. Riser Board
Hard-Disk Drive
One 1-inch-high EIDE hard-disk drive can be mounted to the top of the
expansion-card cage.
Enhanced Dual-Interface EIDE Subsystem
The EIDE subsystem provides two mode-4, DMA bus-mastered EIDE inter-
faces, each of which can support up to two EIDE devices. The EIDE controller
attaches to the high-speed PCI local bus. Any attached EIDE device should be
configured for the Cable Select jumper position. The computer’s boot drive
should be connected to the primary EIDE interface (IDE1).
NOTE: Although the OptiPlex N system board supports up to four EIDE
devices, no devices other than the internal hard-disk drive should be connected.
Built-In Video Controller
The video subsystem consists of a high-speed, high-resolution S3 Trio 64V2
86C785 video controller built into the system board. The video controller con-
nects to the PCI bus, which operates at a frequency of 33 MHz.
The built-in video controller includes 2 MB of video memory built into the sys-
tem board.
PCI1
connector
power LED
Wakeup On LAN
power connector

System Overview 1-5
Optional Built-In NIC
The Dell OptiPlex N computers offer an optional integrated 10/100-Mbps
3Com®PCI 3C905 Ethernet NIC subsystem. The NIC provides all the func-
tions of a separate 3Com 3C905 network expansion card and supports the
100BASE-TX Ethernet standards. Category 5 wiring and connections must be
used.
The integrated NIC does not support the Wakeup On LAN feature. Wakeup
On LAN capability is provided by an optional NIC expansion card such as the
Intel EtherExpress™PRO/100M.
The NIC subsystem connects to the Ethernet network through an RJ45 connec-
tor on the back panel of the computer.
Figure 1-5. NIC Connector on I/O Panel
On computers with the optional built-in NIC, the NIC (RJ45) connector and
NIC interface circuitry are mounted on the system board. The connector
includes the following indicators (see Figure 1-5):
•A yellow activity indicator flashes when the computer is transmitting or
receiving network data. (A high volume of network traffic may make this
indicator appear to be in a steady “on” state.)
•A green link integrity indicator lights up when there is a good connection
between the network and the NIC. When the green indicator is off, the com-
puter is not detecting a physical connection to the network.
“Network Considerations” in the online Network Administrator’s Guide pro-
vides instructions for connecting the computer to, and configuring it for use on,
an Ethernet network.
Stand for Vertical Orientation
The computer can be used in a vertical orientation by attaching an available
stand to the left side of the computer.
NIC connector
link integrity
indicator activity
indicator

1-6 Dell OptiPlex N Systems Service Manual
C
omputer Service
The following subsections provide service-related information about the
computer.
Computer Power Supply
The Dell OptiPlex N computers have an 80-W computer power supply. The
power supply can operate from an AC power source of 115 VAC at 60 Hz or
230 VAC at 50 Hz. The computer power supply provides the DC operating volt-
ages and currents listed in Table 1-1.
NOTE: The power supply produces DC voltages only under its loaded condi-
tion. Therefore, when you measure these voltages, the DC power connectors
must be connected to their corresponding power input connectors on the system
board and hard-disk drive.
.
Table 1-1. DC Voltage Ranges
Voltage Range Maximum Output Current1
+3.3 VDC +3.135 to +3.465 VDC 6.0 A1
+5 VDC +4.75 to +5.25 VDC 12.0 A1
+12 VDC +11.40 to +12.60 VDC 1.0 A2
–12 VDC –10.80 to –13.20 VDC 0.5 A
+5 VFP3+4.75 to +5.25 VDC 1.2 A
1The combined load on the +5-VDC and +3.3-VDC outputs should not exceed 65 W.
2Withstands surges of up to 3.0 A to support disk start-up operations.
3VFP (volts flea power) — sometimes called “standby power.”

System Overview 1-7
Pin Assignments for the DC Power Connectors
The power-supply output voltages can be measured at the back (wire side) of
the connectors without disconnecting them. Figures 1-6 through 1-8 show the
wire side of the connectors.
1Pin 11 — PSON# should measure between +4 and +5 VDC except when the power button
on the front panel is pressed, taking PSON# to its active-low state.
2Pin 19 — Thermal fan-speed control (TFSC) is a power-supply input signal used to control
the power-supply fan speed.
3Pin 5 — PWRGOOD should measure between +4 and +5 VDC when the power supply is
on to indicate that all power-supply output voltages are within the ranges specified in
Table 1-1.
Figure 1-6. DC Power Connector P1
Figure 1-7. DC Power Connector P2
11
1
PWRGOOD
3
(orange)
–12 VDC (blue)
+12 VDC (yellow)
+5 VFP (purple)
common (black)
234 5678 910
12 13 14 15 16 17 18 19 20
P1
+5 VDC (red)
+5 VDC (red)
+5 VDC (red)
+5 VDC (red)
+5 VDC (red)
+5 VDC (red)
common (black)
common (black)
common (black)
PSON#
1
(grey)
common (black)
common (black)
common (black)
open
TFSC
2
(brown)
1234 +3.3 VDC (blue/white)
common (black)
common (black)
5
P2
6
+3.3 VDC (blue/white)
+3.3 VDC (blue/white)
common (black)

1-8 Dell OptiPlex N Systems Service Manual
Figure 1-8. DC Power Connector P3
DC Power Distribution
Figures 1-9 and 1-10 provide the following information about DC power
distribution:
•Power-supply connector identification
•Power cable connection for the hard-disk drive
•Power distribution to sockets and connectors on the system board
Figure 1-9. DC Power Cables
1 2 3 4
+5 VDC (red)
common (black)
common (black)
+12 VDC (yellow)
P3
P3
P2
P1

System Overview 1-9
Figure 1-10. DC Power Distribution
+5 VDC
+3.3 VDC
fuses (2)
core VCC +2.1 to +3.5 VDC
+3.3 VDC
power
management
logic RTC/
NVRAM
+5 VDC
+5 VDC
+5 VDC
+5 VFP
+12 VDC
–12 VDC
+3 VDC
P2
+3.3 VDC
PWRGOOD P1 POWER_1
PSON#
+5 VFP
+5 VDC
+12 VDC
–12 VDC
PSON#
+5 VFP
+5 VDC
+12 VDC
–12 VDC
P3
+12 VDC
+12 VDC
–12 VDC
computer
power supply
keyboard
controller
battery
+3.3 VDC
+5 VDC PCI1
MICROPROCESSOR
PANEL
KYBD
MOUSE
DIMM_A
DIMM_B
main memory
sockets
FAN
RISER
riser board
system board
POWER_2
processorcore
regulator
+5 VDC USB
internal
hard-disk drive

1-10 Dell OptiPlex N Systems Service Manual
System Board
The subsections that follow provide service-related information about the sys-
tem board and its components (see Figure 1-11).
Figure 1-11. System Board Components
primary EIDE
interface connector
(IDE1) (pin-1 corner)
videoconnector
(MONITOR)
diskette/tape drive
interface connector
(DSKT) (pin-1 corner)
riser board
connector
(RISER)
serial port 2
connector
(SERIAL2)
system board
jumpers
NIC connector
(ENET)
control panel
connector (PANEL)
3.3-V power input
connector (POWER_2)
keyboard/mouse
connectors (stacked)
(KYBD/MOUSE)
main power input
connector (POWER_1)
microprocessor socket
(MICROPROCESSOR)
(pin-1 corner)
DIMM sockets (2)
(DIMM_A)
USB connectors (2)
(USB)
front of computer
parallel/serial port 1
connectors (stacked)
(PARALLEL/SERIAL)
battery socket
(BATTERY)
secondary EIDE
interface connector
(IDE2) (pin-1 corner)

System Overview 1-11
Main Memory
The two DIMM sockets on the system board can accommodate combinations of
16-, 32-, 64-, and 128-MB DIMMs up to a total memory capacity of 256 MB.
Although 64-bit nonparity EDO DIMMs are recommended, 72-bit parity
DIMMs can also be installed. The standard main memory is 16 MB of high-
speed (60-ns) nonparity memory. For optimum performance, install DIMMs in
consecutive sockets starting with socket DIMM_A.
System Board Jumpers
Figure 1-12 shows the location of the jumper blocks on the system board. See
Table 1-2 for the jumper descriptions and settings.
Figure 1-12. System Board Jumpers
jumpered unjumpered

1-12 Dell OptiPlex N Systems Service Manual
Table 1-2. System-Board Jumper Descriptions
Jumper Description Settings
133 Reserved Do not install jumper.
166*Microprocessor
speed Install jumper if the microprocessor’s internal speed is 166 MHz; otherwise the
jumper should not be installed.
200*Microprocessor
speed Install jumper if the microprocessor’s internal speed is 200 MHz; otherwise the
jumper should not be installed.
233*Microprocessor
speed Install jumper if the microprocessor’s internal speed is 233 MHz; otherwise the
jumper should not be installed.
PSWD Password
enable or
disable
Install to enable the password features.
Remove the PSWD jumper and boot the
computer to remove an existing password.
BIOS Reserved Do not install jumper.
* One set of the speed jumper pins must have a jumper plug installed; otherwise, the computer will
operate at an undetermined speed.

System Overview 1-13
I
nterrupt Assi
g
nments
Table 1-3 shows the assignment or availability of IRQ lines.
Table 1-3. Interrupt Assignments
IRQ Line Used By/Available
IRQ0 Generated by system timer.
IRQ1 Generated by keyboard controller to indicate that keyboard’s out-
put buffer is full.
IRQ2 Generated internally by interrupt controller to enable IRQ8
through IRQ15.
IRQ3 Generated by super I/O controller to indicate that the device con-
nected to serial port 2 (COM2 or COM4) requires service.
IRQ4 Generated by super I/O controller to indicate that the device con-
nected to serial port 1 (COM1 or COM3) requires service.
IRQ5 Available for use by an expansion card.
IRQ6 Generated by super I/O controller to indicate that diskette
requires service.
IRQ7 Generated by super I/O controller to indicate that device con-
nected to parallel port requires service.
IRQ8 Generated by keyboard controller for each tick of RTC.
IRQ9 Available for use by video controller to indicate that the video or
monitor requires service.
IRQ10 Available for use by an expansion card.
IRQ11 Available for use by an expansion card.
IRQ12 Generated by keyboard controller to indicate that mouse’s output
buffer is full.
IRQ13 Generated by math coprocessor to indicate coprocessor error.
IRQ14 Generated by hard-disk drive connected to primary EIDE port to
indicate that drive requires service. If the EIDE controller is dis-
abled, this line is available for other use.
IRQ15*Generated by device connected to secondary EIDE port to
indicate that device requires service. If the EIDE controller is not
in use, this line is available for other use.
* Although the OptiPlex N system board supports up to four EIDE devices, no devices other than
the internal hard-disk drive should be connected.

1-14 Dell OptiPlex N Systems Service Manual
D
MA Channel Assi
g
nments
Table 1-4 shows the assignment or availability of DREQ lines.
Table 1-4. DREQ Line Assignments
DREQ Line Used By/Available
DREQ0 Available
DREQ1 Available
DREQ2 Generated by super I/O controller to initiate DMA cycle for
attached diskette drive
DREQ3 Available
DREQ4 Generated by bus controller chip to activate second DMA
controller
DREQ5 Available
DREQ6 Available
DREQ7 Available
NOTES: The video controller and optional built-in NIC controller are assigned available
DMA channels automatically during computer start-up.
If the parallel port is in ECP mode, it uses one of the available DREQ lines.