Intermittent problems, Undetermined problems

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.

•Lenovo will not provide replacement if the LCD is within specification as we cannot guarantee that any replacement LCD will have zero pixel defects.

•One pixel consists of R, G, B sub-pixels.

Table 5. LCD-related symptoms

Symptom or error		FRU or action, in sequence

No beep, power-on indicator on, and a blank LCD during		System board.
POST.

• LCD backlight not working.		1.	Reseat the LCD connectors.
•	LCD too dark.	2.	LCD assembly.
• LCD brightness cannot be adjusted.		3.	System board.
• LCD contrast cannot be adjusted.

•	LCD screen unreadable.	1.	See important note for “LCD-related symptoms.”
•	Characters missing pixels.	2.	Reseat all LCD connectors.
•	Screen abnormal.	3.	LCD assembly.
•	Wrong color displayed.	4.	System board.

Horizontal or vertical lines displayed on LCD.		LCD assembly.

Intermittent problems

Intermittent system hang problems can be due to a variety of causes that have nothing to do with a hardware defect, such as cosmic radiation, electrostatic discharge, or software errors. FRU replacement should be considered only when a problem recurs.

When analyzing an intermittent problem, do the following:

1.Run the diagnostic test for the system board in loop mode at least 10 times.

2.If no error is detected, do not replace any FRUs.

3.If any error is detected, replace the FRU shown by the FRU code. Rerun the test to verify that no more errors exist.

Undetermined problems

If the diagnostic tests did not identify the adapter or device that has failed, if wrong devices are installed, or if the system simply is not operating, follow these procedures to isolate the failing FRU (do not isolate FRUs that have no defects).

Verify that all attached devices are supported by the computer.

Verify that the power supply being used at the time of the failure is operating correctly. (See “Power system checkout” on page 34.)

1.Turn off the computer.

2.Visually check each FRU for damage. Replace any damaged FRU.

3.Remove or disconnect all of the following devices:

a.Non-ThinkPad devices

b.Devices attached to the docking station or the port replicator

c.Printer, mouse, and other external devices

Chapter 4. Related service information 45

L420, L520, L421 specifications

The Lenovo L421, L520, and L420 are part of Lenovo's ThinkPad series, which is known for its reliability, durability, and performance. These models are designed primarily for business professionals and students, providing a blend of functionality and portability tailored for everyday computing.

The Lenovo L421 is equipped with the second-generation Intel Core processors, which enhance its performance and efficiency. It features a 14-inch LED backlit display, offering sharp visuals and sufficient screen real estate for multitasking. The L421 also sports a spill-resistant keyboard, ensuring that accidental spills do not affect the device's functionality. This model supports up to 8GB of RAM and incorporates various connectivity options, including USB 3.0 ports, HDMI, and an SD card reader, which makes it versatile for various peripherals.

The L520 is another solid offering from Lenovo, featuring a slightly larger 15.6-inch display for increased productivity. It shares many characteristics with the L421, such as the use of Intel’s second-generation processors. The L520 also emphasizes security with features like a fingerprint reader and a Trusted Platform Module (TPM) for data encryption, appealing to businesses that require stringent security measures. Its ExpressCard and docking station compatibility add flexibility, allowing users to tailor their setups according to their needs.

The L420, like its siblings, comes with an emphasis on performance and utility. With a 14-inch HD display, it offers vibrant visuals. The L420 also benefits from Lenovo's legendary keyboard design, which ensures a comfortable typing experience. This model is geared for users who require a balance between performance and portability without compromising on essential features. The same Intel Core processors and security features are incorporated, ensuring a reliable experience for professional applications.

All three models feature Lenovo's innovative Power Management technology, which optimizes battery life, allowing users to work longer hours without needing to recharge. Additionally, they are built with robust materials that ensure longevity, making them suitable for both office and on-the-go environments.

Overall, the Lenovo L421, L420, and L520 exemplify the ThinkPad series' commitment to performance, security, and durability, making them excellent choices for anyone looking for reliable laptops for professional use.

Lenovo L421 Intermittent problems, Undetermined problems, Reseat the LCD connectors, LCD assembly

Models: L420 L520 L421

Reseat the LCD connectors.

See important note for “LCD-related symptoms.”

LCD assembly.

Intermittent problems

Undetermined problems

L420, L520, L421 specifications