I need help to determine which chip to reflow on my T42

[manteiv]

Hi all,

My computer is T42, type 2373-6ZU with the ATI 7500 chip, running Windows XP

Which chip do I need to heat up? there are 3 of them:
- the one right next to the CPU, with the ATI on it, I believe this is the main GP?
- there is another one (Green square with a smaller inner black square) north of the ATI one
- one south of the ATI one, maked Intel

I acquired this laptop for really cheap on the local classified, it was advertised as non working.

When I first turn ON the machine after I purchased it, I hear the fan spinning but nothing on the screen. I shut it OFF and applied some pressure on the space bar key area and the touch pad. I was able to turn the machine ON and did a clean install of XP.

Now I can turn ON the machine and boot into XP 9 times out of 10. Here are the symptoms, please help me if I need a reflow and which chip I need to heat up.

Symptoms:
- Even if I sucessfully log into Windows, the laptop will eventually freeze by itself after an hour or so (Windows is idle, no screen saver)
- Sometime the computer will freeze just by slightly moving the screen a tiny bit or by flexing the laptop body
- Other times, moving the computer and flexing the body a lot does not cause freezing
- I removed the keyboard, tried pressing down on the ATI and the other 2 chips, sometime a slight pressure on any of those 3 chips cause black screen and freezing. Other time, pressing hard on them have no effect.

Is-it better to use a torch or a heat gun?

[poshgeordie]

Hi and welcome to the forums

I run a reflowing company in UK (see my ad in my signature) and am very familiar with repairing this model.

The three chips you mention:

The "north-most" one is the Northbridge and is completely trouble free so no worries there.

The middle one with ATI on it is the Graphics Chip (GPU) and will cause some of the symptoms you describe, typically:

No picture but everything appears to start up OK.
Display broken up.
Display goes off when you move the laptop.
Laptop will bluescreen and the error message often contains text about missing ATI.exe driver or similar.
You need to press the I/O button for a few seconds to make it turn off.

The "South-most" chip at the front of the motherboard under the wifi card with Intel on it is the Southbridge and will cause some of the symptoms described above, but are also typically:

USB runs at 1.1 rather than 2.0
HDD only works if you press on the chip or on the palmrest next to the Trackpad. Typically the Thinkpad (TP) will appear to freeze and then work again when pressing as described.
No or broken up Audio / no keyboard operation.
On switch on, lights are on etc but no display, but the laptop turns off immediately when the I/O button is pressed (ie not having to press for a few secs as with GPU).

Re using a heatgun etc - there's a sticky about this here, but I must point out that the people who have success with it I think are very experienced at doing it. It is very easy indeed to burn the board / chip because the heat source is much bigger than is needed. Also even with a temperature probe it's almost impossible to accurately measure the surface temperature of the chip. Note also that unleaded solder used on some of these chips melts at around 220deg C, and the component substrate material is destroyed at 250C - a tiny temperature difference.

Alternatively you may want to make use of a new company which is about to be advertised here - The Board Room - which offers refurbished motherboards to North American Thinkpad Forums members, and is run by myself in the UK and RealBlackStuff in US.
At the moment we're looking for broken boards but if you want an exchange one it's possible RBS may have one for you.

Either way please let us know how you get on and good luck!

[pianowizard]

My T42 had the same issue and placing a piece of metal that's about 1mm thick between the GPU and the keyboard fixed the problem. Since then, I haven't had any difficulty turning it on, and it stays on even if I move it. I do try not to move it too much.

[manteiv]

Do I need to scrape off those red epoxy blobs around the edge of the chip first before doing the reflow?

[Bruce Guttman]

Those red epoxy blobs were supposed to be the fix for the poor results with the ball grid soldering.

You will need to remove them (using a Dremel tool and a lot of careful work) since the epoxy will expand during the heating cycle and literally lift the chip off its pads. After you do the reflow and determine that it has done its job, you could place new dabs of epoxy (doesn't have to be red) to try to harden the ball grid array against flexure.