Lenovo T420 - Manual (Page 52)

Beep symptoms
Table 4. Beep symptoms
Symptom or error FRU or action, in sequence
One beep and a blank, unreadable, or flashing LCD. 1. Reseat the LCD connector.
2. LCD assembly.
3. External CRT.
4. System board.
One long and two short beeps, and a blank or unreadable
LCD. 1. System board.
2. LCD assembly.
3. DIMM.
Two short beeps with error codes. POST error. See “Numeric error codes” on page 43.
Two short beeps and a blank screen. 1. System board.
2. DIMM.
Two or more beeps, or a continuous beep. Operating
system starts successfully. If a mini-PCI Ethernet card is installed, confirm that Alert
On LAN 2 in the ThinkPad Setup program is disabled.
Three short beeps, pause, three more short beeps, and
one short beep.
One short beep, pause, three short beeps, pause, three
more short beeps, and one short beep.
1. DIMM.
2. System board.
Only the cursor appears. Reinstall the operating system.
Four cycles of four short beeps and a blank screen. System board (security chip)
Five short beeps and a blank screen. System board
No-beep symptoms
Table 5. No-beep symptoms
Symptom or error FRU or action, in sequence
No beep, power-on indicator on, LCD blank, and no
POST. 1. Make sure that every connector is connected
tightly and correctly.
2. DIMM.
3. System board.
No beep, power-on indicator on, and LCD blank during
POST. 1. Reseat DIMM.
2. System board.
The power-on password prompt appears. A power-on password or a supervisor password is set.
Type the password and press Enter.
The hard-disk password prompt appears. A hard-disk password is set. Type the password and
press Enter.
LCD-related symptoms
Important: The TFT LCD for the notebook computer contains many thin-film transistors (TFTs). The presence of a
small number of dots that are missing, discolored, or always lighted is characteristic of TFT LCD technology, but
excessive pixel problems can cause viewing concerns.
If the LCD you are servicing has two or less visible defective pixels, it should not be considered faulty. However, if the
LCD has three or more visible defective pixels, it will be deemed as defective by Lenovo and it should be replaced.
Notes:
• This policy applies to all ThinkPad Notebooks purchased on 1 January, 2008 or later.
46 ThinkPad T420 and T420i Hardware Maintenance Manual