Entering Service Mode; Exiting Service Mode; Safety Precautions - Dell Latitude 3420 Service Manual

3. Disconnect your computer and all attached devices from their electrical outlets.
4. Disconnect all attached network devices and peripherals, such as keyboard, mouse, and monitor from your computer.
5. Remove any media card and optical disc from your computer, if applicable.
6. After the computer is unplugged, press and hold the power button for 5 seconds to ground the system board.
CAUTION: Place the computer on a flat, soft, and clean surface to avoid scratches on the display.
7. Place the computer face down.

Entering Service Mode

Service Mode allows users to immediately cut off electricity from the computer and conduct repairs without disconnecting the
battery cable from the system board.
To enter Service Mode:
1. Shut down your computer and disconnect the AC adapter.
2. Hold <B> key on the keyboard and press the power button for 3 seconds or until the Dell logo appears on the screen.
3. Press any key to continue.
NOTE: If the power adapter has not been disconnected, a message prompting you to remove the AC adapter appears
on the screen. Remove the AC adapter and then press any key to continue the Service Mode procedure.
NOTE: The Service Mode procedure automatically skips the following step if the Owner Tag of the computer is not
set up in advance by the manufacturer.
4. When the ready-to-proceed message appears on the screen, press any key to proceed. The computer emits three short
beeps and shuts down immediately.
Once the computer shuts down, you may perform the replacement procedures without disconnecting the battery cable from
the system board.

Exiting Service Mode

Service Mode allows users to immediately cut off electricity from the computer and conduct repairs without disconnecting the
battery cable from the system board.
To exit Service Mode:
1. Connect the AC adapter to the power-adapter port on your computer.
2. Press the power button to turn on the computer. Your computer will automatically return to normal functioning mode.

Safety precautions

The safety precautions chapter details the primary steps to be taken before performing any disassembly instructions.
Observe the following safety precautions before you perform any installation or break/fix procedures involving disassembly or
reassembly:
● Turn off the system and all attached peripherals.
● Disconnect the system and all attached peripherals from AC power.
● Disconnect all network cables, telephone, and telecommunications lines from the system.
● Use an ESD field service kit when working inside any to avoid electrostatic discharge (ESD) damage.
● After removing any system component, carefully place the removed component on an anti-static mat.
● Wear shoes with non-conductive rubber soles to reduce the chance of getting electrocuted.
Standby power
Dell products with standby power must be unplugged before you open the case. Systems that incorporate standby power are
essentially powered while turned off. The internal power enables the system to be remotely turned on (wake on LAN) and
suspended into a sleep mode and has other advanced power management features.
8 Working inside your computer