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These are some common tools used to work on this device. You might not need every tool for every procedure.

How the T420i varies from the T420 ¶ 

The T420i is similar in the sense it shares the same chassis, but the machine is just not as common. The differences between the standard T420 and T420i aren't substantial enough to affect the average person buying a secondhand one, but you should be aware of the limitations the T420i has the standard system does not.

  • Processor: The T420i ships with the Core i3 2310M processor, which makes it somewhat unique. This processor was never offered on the standard T420.
  • Advanced management (vPro/Computrace): Since these systems ship with the Core i3 2310M, the BIOS does not have any vPro licensed code. However, the Computrace Persistence module is available.
  • Graphics cards: The T420i only shipped with the Intel IGP graphics. It was never offered with dedicated graphics.
  • RAM: This machine only accepts 8GB, officially. The Core i3 2310M supports 16GB per Intel's ARK documentation.
  • Ethernet: The T420i uses a Intel 82577LC Ethernet chipset, rather then the 82577LM chipset found in the standard T420.

The FRU numbers between the machines are more or less the same, with the exception of the motherboard (no Intel AMT or vPro). The AMT/vPro board can be installed, but it does not come with it from the factory.

Overall, the T420i isn't much different from the T420. The primary differences are the motherboard, official RAM capacity and a lack of Intel AMT and vPro. The machines are also serviced the same way as a standard T420.

Machine identification ¶ 

You can identify your machine as a ThinkPad T420 or T420i by looking at the bottom right corner of the LCD bezel. The model of the machine is printed in this location.

Block Image

To identify the factory specifications, look for a 7 digit System Type. It will look something like this:

Block Image
  • Ready to ship: XXXX-XXX

To find the specs on a machine with a CTO SKU, you will need to look up the system serial number and see what Lenovo lists under Machine Info in Lenovo Support. For ready to ship models, it can generally be found with a Google search or through Lenovo Support.

To locate the serial number, look on the same sticker that has your system SKU number. It should read like this: S/N XX-XXXXX. To locate the factory specs on a CTO model, you will need this to determine the exact specifications of the system, but it can also be used to determine if a ready to ship model has been customized with extra hardware or ordered with extra accessories when purchased, like extra batteries. It is also required to check the warranty on the system, and will tell you when the system was purchased.

Processor ¶ 

Non vPro

  • Intel® Core™ i3 2310M (2.1GHz, 3MB L3, 1333MHz FSB) Note: T420i only.
  • Intel® Core™ i5-2410M (2.3GHz, 3MB L3, 1333MHz FSB)
  • Intel® Core™ i5-2450M (2.5GHz, 3MB L3, 1333MHz FSB)


  • Intel® Core™ i5-2520M (2.5GHz, 3MB L3, 1333MHz FSB)
  • Intel® Core™ i5-2540M (2.6GHz, 3MB L3, 1333MHz FSB)
  • Intel® Core™ i7-2620M (2.7GHz, 4MB L3, 1333MHz FSB)
  • Intel® Core™ i7-2640M (2.8GHz, 3MB L3, 1333MHz FSB)

Most machines use the Core i5 2520M. There are systems with i7 processors, but these are rare and are likely to be upgraded processors, unless you can verify the system shipped with it by looking for a sticker with a Lenovo FRU or checking online.

Note: Lenovo did not ship these systems with quad core processors. Systems with a QM part installed are user upgraded. Do this upgrade at your own risk.

Memory ¶ 

Most T420 systems ship with ~4GB of RAM, unless it was upgraded by the previous owner or shipped with more memory then this from the factory. On a non CTO SKU, you can quickly figure this out by googling the system type. On a CTO SKU, run the serial number through Lenovo's support page. Look at the Machine Identification section to see how to identify if you have a CTO or Ready to Ship model, and find your system serial number.

Memory capacity and type (Official)

  • Memory type: DDR3 1.5V
  • Memory speed: 1333MHz (Recommended)

Maximum supported memory:

  • T420: 16GB
  • T420i: 8GB

Memory capacity and type (Unofficial)

Disclaimer: I have not tested this. This information is from Intel's ARK documentation. As such, you try this at your own risk with no support from Lenovo.

  • Supported Memory types: System and Processor dependent. You will have to check if the processor installed supports DDR3, or supports both DDR3 and DDR3L. DDR3L has not been tested in the T420. As such, your mileage will vary.
  • Memory speeds: 1600MHz (downclocks to 1333MHz) or 1333MHz

Maximum supported memory:

  • T420 (With Core i7 upgrade): 32GB
  • T420i (Core i3 or i5): 16GB

Notes regarding DDR3L

General information

  • DDR3L is likely to be accepted, but may not run at 1.35V. Sandy Bridge is DDR3L aware, but is not officially supported. This applies to both the T420 and T420i. I would recommend dual voltage modules (1.5V/1.35V compatible) to ensure compatibility, or purchasing traditional 1.5V memory. Dual voltage modules are likely to work, but may not run at 1.35V.
  • If dual voltage memory is installed and is accepted at the 1.35V voltage level, you will see marginal improvements in battery runtime.
  • You may see a slight CAS rating improvement if the modules run at 1.35V. However, this WILL NOT be the case if the system runs these modules at 1.5V.
  • WARNING: If you install single voltage DDR3L modules and it does not work, your system will fail POST.


  • If the modules are accepted at 1.35V, run something like Memtest 86+ for ~6-8 hours to test for stability. If the system can hold a memory test this long, you're not likely to run into a problem. Note: This is NOT required with single voltage modules, as the system will fail POST if it doesn't accept them.

Hard Drive ¶ 

This machine can run with 2 drives installed. It can take an mSATA SSD and a 2.5" SATA hard drive.

Note: While the WWAN slot can accept a mSATA SSD, the slot will only run the SSD at SATA II speeds This does not happen with normal SATA drives.

While the WWAN slot only runs at SATA II speeds, this is sufficient for a small boot SSD. It is recommended that this is supplemented by a spinning hard drive for mass storage.

Important: The SATA spec on this machine is unclear. I have been told it is SATA III, but Lenovo has only validated SATA II drives on this machine. Make sure you use a drive with a reliable SATA II fallback mode.

Video cards ¶ 

This machine shipped with 2 configuration options

  • Intel HD Graphics 3000
  • Intel HD Graphics 3000/nVidia NVS 4200M (nVidia Optimus enabled)

Important: When you are buying the system, decide if you want a iGPU or Dual GPU system BEFORE you buy, if you care about this. If you get a Intel only one, you are stuck with Intel video and CAN NOT add a dGPU.

WiFi ¶ 

Warning: This machine has a WiFi whitelist. You will need a no WL BIOS to install non Lenovo WiFi cards. If you do not do this, you will get an 1802 error at POST and halt the system.

Supported cards:

Supported, but not recommended:

  • ThinkPad BGN (RealTek - Stockton) 1x1 BGN
  • Intel Centrino Wireless-N 1000 (Condor Peak) 1x2 BGN

Supported Recommended cards

  • Intel Centrino Advanced-N 6205 (Taylor Peak) 2x2 AGN
  • Intel Centrino Ultimate-N 6300 (Puma Peak) 3x3 AGN

You must buy a card that has a Lenovo FRU on the label to ensure compatibility. Unless you are willing to flash a no WL BIOS or alter the card's PCI ID to get around the whitelist, you will need to make sure you have a Lenovo card. It helps to know the FRU of the card you want, to make it easier to find.

Computrace (And how to identify it) ¶ 

These machines support the Computrace Persistence Module. This can be a problem if the subscription was left on the machine itself before sale. It is important to check this before buying the machine. To do this, do the following:

  • Boot up the machine, and get to the BIOS. You can do this in a few ways, but the easiest way to do it is to press F12 and load the BIOS from this menu.
  • If the machine warns you that Computrace is active and the option is locked in as Enabled, with the option to change it grayed out, you have a residual Computrace subscription. DO NOT use the machine in this state.

This is what you will see if you have a Computrace system:

Block Image

To remove it, simply contact Absolute Software and they will help you. If the machine is legitimate, it should be gone in a day or two. If it is not, try again with another rep. You will likely need a receipt or some notarized document to get them to do it, unless you get lucky.

BIOS passwords ¶ 

There are 3 BIOS password levels one can install on the system. Some are worse then others, but here's the list:

  • Admin password/SVP. If your machine has one of these, you need to replace the motherboard to fix it.
  • POP: This can be cleared by removing the CMOS battery. BE WARNED that doing this with a SVP on the machine will default the system to the SVP and you will be in a world of hurt when this happens.
  • HDP: This is applied to the hard drive. In order to remove this, you will have to toss the hard drive and replace it. It may come back when the drive is replaced, so use a test drive you do not care about to make sure it will not come back if you replace the drive. If it does, you will kill the test drive and have to mess with the machine further to fix it.

WWAN cards ¶ 

Note: All supported WWAN cards are nearly or fully obsolete. Use an external device, like a mobile hotspot or install a no WL BIOS.

The vast majority of machines are billed as WWAN upgradeable. This means the machine has the antennas and SIM slot installed, but does not include the card. The WWAN card goes next to the bottom RAM slot.

Supported cards:

  • Ericsson F5521gw (3G/HSPA+/GSM capable)
  • Sierra Wireless Gobi™ 3000 (HSPA/CDMA EV-DO)


Dual network cards (GSM and CDMA):

These cards must be released from the previous account, if the system was previously used on a CDMA provider. If the card was used on a CDMA network and was not released, the card is useless. This is because CDMA relies on an embedded SIM card, and the account data will be stored on this embedded SIM card. Even if you tore into the card and cleared the chip out without killing the card, it is still registered with the previous carrier and they will reject it.

There is a potential exception here: If the card was on a GSM network, you MAY be able to use it anyway. Do not count on this, but it's something that may end up working. This may work, since the embedded SIM is not being used; rather, an external SIM card under the RAM door is used. BE WARNED the card may be blocked, if the seller retained the IMEI number. If the seller or previous owner did not do this, you should be in the clear if the card has been released from the previous account and the seller did not retain the information from the card.

GSM only: These cards are relatively safe, compared to dual network cards. These do not require account removal like CDMA cards do, but failing to do this may end up "bricking" the card, should the IMEI ever get blocked. I recommend getting the seller to tell you it is clear, or have them do it before you buy the card, if this is at all possible. If you can't do this, you are buying the card with the risk it will be blocked at any time, without warning. The service is tied to the SIM card on these cards, but the IMEI can be blacklisted, which will kill the card.

To recap:

  • Dual network cards with a residual CDMA account are useless. Check for a residual account on machines that mention mobile broadband from Verizon or Sprint, or if the card came out of one of these systems, verify it is clear to use before buying it.
  • CDMA cards must be clear to use them, especially if the previous account is with Verizon or Sprint.
  • GSM only is safer, and can likely be on multiple accounts.
  • GSM can still be blocked via the IMEI.
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