Lenovo Thinkpad T61 GPU fix. Or not.

My mobile workhorse is a trusty Lenovo T61, a close cousin of the ones they use on the International Space Station. How cool is that? It’s built like a tank, and weighs about as much, but the feature I appreciate most is its screen: a lovely 1680 x 1050 resolution, which is actually enough pixels to get some work done. Most laptops have rubbish screens which were clearly only designed for watching DVDs and reading Facebook. It’s a pet hate of mine.

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Sadly the Thinkpad has blotted its copybook. The Nvidia graphics chip has a reputation for expiring earlier than it should do, and this one has. It started with the screen going blank a couple of months ago. I replaced the screen, and then it worked but only with every other column of pixels. Then it spontaneously started working almost-properly, but with a peculiar green shimmering effect on bright colours which was just about possible to avoid by fiddling with the display settings. Then it died altogether, and just gave the ominous beep-bip-bip code at startup which means ‘my graphics hardware isn’t working’.

In a last ditch attempt to revive it, I thought I’d try reflowing the solder on the graphics chip. It helps on some laptops. In theory you need very specialised equipment for this, but I’ve had success in my professional life doing it with a more, shall we say, agricultural approach. With nothing to lose, I had a go. Here’s what I did.

Reflowing the solder on the graphics chip involves removing the motherboard, which requires completely disassembling the laptop.

Remove all the bits the come out: the battery, DVD drive, hard drive, and any PC card and SD card.

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Remove the marked screws  on the bottom to remove the keyboard, touch pad and palm rest.

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Unplug the three wires to the Wifi module. Plug 1 is grey, 3 is white, 2 is black.

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Remove the keyboard surround/speaker grills. Two short screws on the top, one long one from the bottom rear right corner, one long one from the outer rear bottom left corner, four little flat ones from the metalwork near the CPU.

Unplug the screen connector, the grey cloth one near the fan.

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Remove the two tiny screws holding the left speaker and move it to one side.

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Remove 2 medium-length screws from the bottom rear edge and two short screws from the screen brackets on the top side. Take the screen off.

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Remove one tiny silver screw from the front right hand side, 9 short screws from the bottom, three more long ones from the bottom, and four short ones with big flat heads near the docking connector.

From the top, remove the four medium-length screws holding the heatsink down.

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Remove the two short silver screws holding the two silver brackets on the right side of the heat sink.

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Unplug the fan connector and ease the heatsink/fan assembly free.

 

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Unplug the multiway connector in the rear centre which feeds the USB sub-board. Tease the wire free from under its sellotape.IMG_1253

Remove the two medium screws holding the wifi module in and remove the wifi module.

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The motherboard and frame should now be free of the bottom case.

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Turn the motherboard over. Remove the 8 remaining screws with big flat heads. Remove the medium screw by the DVD connector. Remove the small silver screw by the SD socket. Remove the short screw holding the heatsink brace. Remove the heatsink brace.

Returning to the top of the motherboard, unplug the charger connector, the small connector by the phone socket, the speaker connector by the RAM and the little black connector at the back where the wifi module was. Leave the backup battery connected.

The magnesium frame should now be free of the motherboard. Take it off. Clean the heatsink compound from the tops of the large chips. U47, with the Nvidia logo on it, is the GPU.

To try and reflow it, I made a makeshift heatshield out of a doubled-up piece of kitchen foil. I’ve done some emergency BGA repairs in the past so I had some idea of what I was aiming at. My strategy is to heat the whole chip area while carefully poking some nearby easy-to-repair part to see when the solder has melted. I expected it to take a couple of minutes.

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I did exactly that, but ran into a nasty problem: there is self-adhesive tape on the top of the GPU and nearby on the PCB, which shrinks in the heat. Unfortunately it takes components with it, so they end up on the tape instead of the PCB. It turns out that there are a couple of dozen parts – decoupling capacitors, I think – on the top of the GPU. Most of them had come off and stuck to the shrunken tape.

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In addition, the backup battery got itself in the way and overheated and burst during the reflow. There were also solder balls visible round the end of the GPU. I thought I’d pretty much wrecked it. But, having come this far, I decided to try and repair the damage and put it back together.

Reassembly is the reverse of disassembly, as they say in the Haynes manuals. Don’t forget to apply new heatsink compound to the tops of the chips in contact with the heatsink. I didn’t hold out much hope.

I got it all back together with no screws left over. I put the battery in, pressed the power switch, and apart from a brief flicker of the power light, nothing. Not a sausage, or even a beep. Game over. Time to go shopping for a new motherboard.

As luck would have it, the Thinkpad T61 was built in various versions. Only the really upmarket ones have the Nvidia graphics chip with the bad reputation. The cheaper versions use the graphics provided by the Intel motherboard chipset. I care more about reliability than I do about ultimate 3D graphics performance, so I decided to do a motherboard swap once I’d discovered that replacement motherboards were available from the US at about $30. It’s useful to know the part numbers. My original motherboard, an early one with Nvidia graphics, was a 42W7652. The ones with the Intel graphics are 42W7651 (early version, supports Intel Merom processors) and 42W7875 (later version, supports both Merom and Penryn processors). On the left the old motherboard, on the right the replacement one.

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Swap the CPU and RAM to the new motherboard, and make sure you put the little foam block on top of the transistors by the VGA socket – it conducts heat to the heatsink. Also swap the PC Card cage, which is held by two screws underneath the motherboard. It pulls out vertically from the motherboard.

Getting the machine to boot after I’d swapped the motherboard took a bit of fiddling. It turns out that, because the backup battery had been removed, all the BIOS settings were lost and the SATA interface mode had changed from ‘Emulation’ to ‘AHCI’. The symptom was that the machine would start booting but Windows 7 would just bluescreen immediately. Changing that BIOS setting fixed the problem.

I didn’t have to re-validate Windows, but a couple of pieces of software got unhappy. The Visagesoft Expert PDF tools required me to re-enter the registration information I’d already paid for, which was no trouble, and the Xilinx and Lattice FPGA tools needed new host-locked licence keys generating, which was free.

The Thinkpad lives to fight another day, and to let me write this blog post.

 

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One thought on “Lenovo Thinkpad T61 GPU fix. Or not.

  1. S. Petkov

    Thanks, it gave me a clue about the starting beeps + grey screen and missing ThinkPad boot screen.

    Reply

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