T41p Laptop CPU Upgrade
Copyright 2007 Sean Long
My laptop computer is primarily intended to be used on the road, during both work trips and on vacation. Because laptops are fairly expensive, I have had a lot of luck buying the best, top of the line laptop I can find and then using it as long as possible. My first laptop was a Zeos 386, and that lasted me about 5 years. My second laptop was a top-end Micron XKE Pentium 266MMX, and that lasted me about 6 years and was only replaced because the newer video codecs simply could not work on the original MMX Pentiums. My current laptop is an ibm T41p, which I have had for just over 3 years. As far as capabilities go, the laptop still works and feels as if it is brand new. I have upgraded the memory to 2gb, upgraded the removable optical drive to a DVD burner, and am on my second battery. About a year ago I learned that with a simple BIOS flash, the original 1.7 ghz pentium M "Banias" cpu (130nm process, 1mb L2 cache) that came standard with the T41p can be upgraded to a 2.0 ghz Pentium M 755 "Dothan" cpu (90nm process, 2mb L2 cache) which was available in the later T42 models. A short article describing the difference between Banias and Dothan Pentium M cpus can be found here, and a more detailed article covering the Pentium M architecture can be found here.
At the time I heard that a CPU upgrade would be possible, a loose Pentium M 755 cost around $350, which is a bit high for a mere 300mhz boost. When I recently found a new still in-the-box cpu on eBay for $160, I couldn't resist the chance to boost my laptop to the faster speed. It should be noted that the T41p could probably use a 2.1 ghz Pentium M 765, but those cpus are still over $300 at this time and because relatively few of these faster processors were manufactured, they will likely remain expensive until they are obsolete.
Before I go any further, you should know that this upgrade is not for the novice or fumble-fingered. There are any number of ways you can completely destroy your computer during an upgrade of this type. From losing tiny screws to shorting out the motherboard with static electricity or dropping a screwdriver into the open computer, this is not a project for someone who is not already fairly competent wielding a screwdriver and performing computer upgrades. If you break it, chances are your warranty has also expired and you'll be left with a new matte-black doorstop.
Still, the instructions in the service manual are fairly clear and the system is quite well designed to be user and field serviceable, so if you have any experience in computer building, repairs, or upgrades you should not have any major problems.
First things first. Here is the computer, before I did anything to it.
|The T41p closed [View larger]||The T41p open [View larger]|
(The dirty screen is embarrassing!)
|The new CPU [View larger]||Only two "tools" [View larger]|
Above left is the CPU I will be installing:
Preparing for the work, I went to IBM's (Now Lenovo's) website and downloaded the T41p service manual. IBM/Lenovo do their customers a great service making these manuals available and this is something all laptop manufacturers should do. Here are the only tools I needed - A screwdriver and some artic silver 5 thermal paste. Again, kudos to IBM for an extremely well thought-out design requiring minimal tools.
Beginning the computer teardown, I first removed the battery and hard drive.
|Inverted, battery out [View larger]||Sliding out the hard drive [View larger]|
Removing the hard drive probably isn't required, but it's a good protective measure to remove it while poking around inside. This presented me with the teardown's first gotcha - the hard drive will not come out while the lid is closed and latched because the hard drive chassis cover catches on the LCD lid bezel.After the hard drive is removed, it is time to remove the keyboard. This is accomplished by removing 4 screws from the back of the laptop, flipping the laptop over and opening it up, sliding the keyboard towards the display about 1/8th of an inch, and lifting at the bottom of the keyboard to remove. Underneath the keyboard is a flexible ribbon cable that must be removed. Set aside the keyboard and stare in amazement at IBM's work of art!
|Inside the T41p [View larger]|
It should be noted that this is as far as you have to go in order to replace the second memory chip (clearly visible in the picture with the crucial.com sticker). We're digging deeper, so the next step is to remove the palm rest. Again, this is accomplished by removing screws from the bottom, but this time it requires 8 screws and 5 small screw-hiding stickers to be removed. The palmrest lifts straight out and again there is a short ribbon cable to disconnect, this time for the touchpad. Once you have this removed, we can see the wireless card and it's two antenna cables, and some more neat stuff. Avoid the temptation to poke around too much, since we haven't removed the CMOS battery so some circuits may still be live and any static electricity could burn out anything you touch.
|Palm rest gone, too [View larger]|
I usually recommend a grounding strap when working on computers but it's not obvious where you'd attach one to a laptop while disassembling it. I made do by making sure I touched a finger to the metal chassis before touching anything else and hoping for the best. I guess it worked because I didn't kill the computer.
|Bezel detached [View larger]|
The next step is to remove the keyboard bezel by removing 3 screws and lifting it out. It should be noted that this is the first place where those irritating little plastic clips are used. You know the ones I'm talking about, the ones that feel like you're going to break off when you remove them, and then you can't get them all lined back up and clicked into place when putting everything back together. Well, this bezel has a half-dozen clips of various sizes and types, so be patient and take your time. In the next picture, you can see the bezel is removed which will give us enough clearance to lift out the copper heat-pipe cooler and fan unit.
The next step in the manual is to remove the LCD display because there is a structural bar over the exhaust fins of the heatsink, but I decided to skip this rather lengthy step and go straight to removing the heatsink. Look closely at the heatsink, and you can see it is copper, has multiple heat-pipes, and it also covers both the cpu and video chip. This presented the next challenge. After removing three spring-loaded screws that hold the heatsink over the cpu with a measured amount of pressure, and disconnecting the fan power connector, it appeared as if the heatsink should come right out. To ensure a reasonably good contact between the video chip and heatsink, IBM chose to use a thermal pad over the video chip. These thermal pads are not particularly effective and in this case, they sealed the thermal pad and heatsink to the video chip with some black tar-like sealant. It was not clear how strong the bond was, so it took me quite a while to separate the heatsink from the video chip without breaking anything or ripping the graphics chip right off of the motherboard. Fortunately the video chip package has an integrated heat spreader on top so some careful prying between the video chip and heatsink freed it. At that point, the heatsink could be fairly easily removed even with the bracing I mentioned before still over the heatsink exhaust fins.
|Heat sink off [View larger]|
Lifting the heatsink off, here is what I found.
You can clearly see the cpu with white thermal grease (still soft and moist unlike poor-quality silicone based pastes which can dry out), and the ATI fireGL T2 video chip. This video chip is actually a multi-chip package, with GPU and on-board memory all on one package covered by a heatspreader which is stamped with the ATI logo and some other interesting details. Underneath the heatsink, you can see the spot where the cpu contacted the heatsink (the white rectangle of thermal grease) and the pinkish colored thermal pad that contacts the video chip. The image is fuzzy because the auto-focus went wonky and I didn't notice until it was too late.
|Heat sink, fuzzy [View larger]|
The cpu is released from the socket after turning a small screwhead 180 degrees. I didn't take a picture of the empty socket, but rest assured it looks like any other empty socket. I installed the new Pentium M 755, and closed the socket again by turning the screwhead back 180 degrees. From the pictures, you may be able to see the packaging difference between the different cpu generations - The Dothan cpu has a slightly more rectangular chip package housing a cpu built on a smaller manufacturing process and containing 2mb of level 2 cache as opposed to the earlier Banias 1mb cache. This doubling of cache was made possible by shrinking the manufacturing process from 130nm to 90nm.
|Dothan CPU in place [View larger]|
I did not take any pictures from this point since it was essentially the disassembly process in reverse, however there was one critical step remaining before putting everything back together. To ensure a proper thermal transfer from the cpu core to the heatsink, a layer of heatsink paste MUST be properly applied between the cpu and heatsink. A very thin layer is normally preferred, however since I cannot verify the interface quality in this installation I installed a somewhat thicker layer than I would for a desktop cpu. I used Artic Silver 5 (AS5), one of the best non-silicone pastes on the market. There are newer pastes that work about the same and are slightly easier to spread, but very few are as good as AS5. Since I was putting a faster and potentially hotter cpu inside this laptop, I wanted to ensure the best possible interface for thermal transfer. The service manual says to put the thermal paste on the heatsink, but I think a better method in this case is to put the thermal paste on the cpu itself. I prepared the heatsink surface by cleaning it with rubbing alcohol to remove the old paste, and then rubbed a small amount of artic silver into the heatsink to help fill in any pores and grooves in the metal before replacing it. This technique is reputed to aid the interface quality for heatsinks that directly contact the cpu die, as in this application.
After re-assembling the computer in reverse order from the disassembly, I fired it up and watched my upgraded computer come to life. It booted a little bit quicker than usual, but otherwise acted normally. I used the nifty CPU-Z utility to verify the cpu clock speed and type, and ran a short burn-in test to heat up the cpu and ensure it would not overheat. Happily, the stock cooling seems to do a fine job keeping the cpu cool and the exhaust air is nice and warm which tells me that the thermal interface is doing a good job transferring heat from the cpu to the heatsink. Benchmarks quickly showed the new cpu to be giving me around 15-20% more performance, exactly what I expected from the 300mhz jump and doubled L2 cache. There are other minor tweaks between the Dothan cpu cores and the older Banias cores, so overall this should give me just a little more speed for the remaining years of this laptop's useful life. The only drawback so far is that the new cpu apparently uses approximately 15% more power at idle than the old cpu in spite of the newer 90nm core and slightly lower operating voltage, so I expect to see a corresponding drop in battery life. As I get over 4 hours of real use out of the high-capacity battery, I do not expect this to be a significant drawback.
That's my experience and mini-tutorial on upgrading the CPU in an IBM T41p laptop. I hope you found it interesting, and if you also own an IBM T-4x series laptop, maybe even a little helpful. The last BIOS for the T-4x series laptops gives most of them full Dothan cpu compatibility so this is a fairly cheap way to get a little more life from these powerful and remarkably durable laptops. Because I was upgrading a computer that shipped with the fastest available CPU at the time, anyone with a T-4x series laptop that came with an even slower CPU will see a lot bigger performance gain from the upgrade. As usual, your mileage may vary and I can't be liable if you break your computer trying to duplicate my upgrade. But as my total time spent performing this upgrade was right around 1.5 hours, it is certainly not the most difficult upgrade I've ever accomplished.