OK (deep breath!) - we need to remind ourselves about what the problem is with the Nvidia GPU.
The problem is due to fundamental design faults with the chip. Over time, as the chip goes through the normal hot and cold cycles in normal use, the tiny solder joints (called High Lead Bumps) connecting the chip layers together break.
Also the filler material between the chip layers is too soft and doesn't support the layers properly.
For more detailed information please read an article I wrote on Thinkpad Forums:
Nvidia GPU - Problems and "Solutions". (BTW I have no problems with this being translated and republished on this forum.)
It is NOT due to unsoldered solder balls as in T4x ATI and Intel Southbridge chips.
So, as Punto asks, is a simple reflow going to fix the problem? The simple answer has to be "no", since how can any reflow or heating process fix manufacturer design faults?
The next question is whether it's possible to simply remove the broken chip and fit a good redesigned chip? I am not aware that Nvidia every made redesigned chips and there's a part of me that thinks that they probably haven't because they want people to just buy new laptops with newer GPU's and trash their broken ones.
But I've read somewhere in these forums that they are using new chips in Asia to repair laptops. But are they original designed chips which will have the same problem in future?
We have tried to buy supposedly new replacement chips in the past and have been sent old chips which have been removed from broken laptops and then reballed. One was even "blown out" ie the top surface of the chip had detatched from the rest of the chip with bubbles over the surface - 100% useless!
The next problem is how to remove these chips from the T61 motherboard. Lenovo has glued the chips to the motherboard with clear epoxy and this has to be removed before unsoldering and lifting the chip.
We have found no way of removing this epoxy. Heat doesn't work and nor does trying to dissolve it with chemical solvents. If we try to lift the chip with the epoxy still in place, tracks and solder pads on the motherboard are also pulled off the motherboard.
The only solution is to grind the chip off the motherboard using a Dremel tool. This is a very long and dangerous job since it's extremely easy to make a tiny slip and cause unrepairable damage to the motherboard.
We have never tried this on a T61 board, but have done it many times on Southbridges on T42p and T43 boards.
So the final option is to try and repair the existing GPU chip, and to find a way of soldering the layers of the chip together.
We have repaired many HP, Sony, Dell etc etc, with these Nvidia GPU's but not many T61's. We have developed a special heating profile on our Infrared Reflowing Station, and we repair around 90 - 95% of chips by this method.
The length of time the laptop continues to work then depends on how damaged the chip is before we repair it, and this is around 70 - 75% which work for at least 90 days (our warranty period) or beyond - not a good number.
The next thing is to reduce the repaired GPU operating temperature. We clean the Fan Assembly of dust (usually very dusty!) and then replace any plastic flexible blue heatsink material between the chip and heatsink with exactly the right thickness of copper shim. Some laptops don't need them, but where they are needed every shim is of slightly different thickness and we make each one individually in-house for each laptop.
The copper shim is kept in place with very thin layers of Arctic Silver heatsink compound on both sides of the shim, and the shim improves the heat dissapation from the GPU to the Fan Assembly.
Moving onto the software side - the first and most important things to do is to install the recommended BIOS which for these laptops (HP, Dell, Lenovo etc etc) usually has the effect of turning the fan on, either permanently, or at lower operating temperatures.
Also the latest recommended laptop manufacturer Nvidia GPU driver should be installed. These should be optimised for the laptop model.
The next area is to underclock the GPU slightly, again to reduce the operating temperature. Nvidia GPU drivers for these chips include
Powermizer, a battery and power optimising program.
Powermizer Manager lets you change the performance (ie clock) settings of the chip and helps to reduce the chip operating temperature. Please be aware that it's possible to damage the GPU with this program.
There are other similar programs available. Same warnings etc.
As I've said earlier we don't repair many Nvidia chipped T61's but have done many, many other laptop makes with the same chip family. In particular HP DV and TX series, Sony Vaios, Dells, Acer, Samsung (R700), Rock, etc etc.
My personal opinion is that it's a very poor situation and that laptop owners have been badly let down by buying laptops with this GPU family in good faith, and are now sitting on a piece of equipment which will almost certainly go wrong due to no fault of their own, and with no means of redress from the chip manufacturer.
This compares with the USA where some laptop owners have won a
Class Action against Nvidia. Why is there nothing like this in Europe?
Again apologies for writing in English. Please translate into German if necessary!
Auf Kulanz seitens Lenovo kann ich vermutlich nicht hoffen. Von Ralf Scharbert habe ich noch "Gewährleistung" (dachte, es sei Garantie), aber das ist auch schon 8 Monate her.. > über 6 Monate. Hoffentlich ist der Mann kulanz, sonst kann ich das Ding gleich wegwerfen. 
Stand nun auch vor der Entscheidung und kann nun guten Herzens sparen!
