Asus F3T Northbridge burning

[Th3_uN1Qu3]

I've had this laptop around for a while. The guy who sent it to me said he got it for free and wants to get it fixed. The trouble he had with it was that it would shut down after a couple minutes, and an area under the keyboard (where the Northbridge is) would get crazy hot. Then it died entirely and would not power on at all anymore, just the power led was lit.

This laptop has AMD processor, nVidia GO6100 northbridge, nVidia GO7600 GPU. The GPU seems to have been reballed before, but looks fine.

The LAN chip was getting very very hot so i removed it. Then i noticed a little vreg was getting hot too. I found a short on the parts under the MCP67 southbridge. Removed the MCP67 and the short went away. Replaced with known good chip and the short was back.

I've left it aside for a while and went back at it today. Of course, it was a minuscule ceramic cap that caused the short.

Now the laptop powers on and displays, but i guess we're back to the original issue: The heat output of the Go6100 is ridiculous. I've put a small heatsink (from a southbridge of a desktop board) over the NB for testing purposes. After a few minutes, the heatsink reaches 120C! And it's supposed to dissipate all that heat IN THE KEYBOARD???? Crazy. Out of curiosity, i lifted the heatsink and put the temperature probe on the die of the NB. In a few seconds, it reached over 140C and then the laptop shut down. Put the heatsink back on and it still works...

The Go6100 could be defective, and i have a few SPP100 (which will work since it's got dedicated video), so replacing it wouldn't be a problem. But i think i'll check the power supplies first. If the Go6100 were bad, the laptop wouldn't work at all...

[Th3_uN1Qu3]

Re: Asus F3T Northbridge burning

Damn, this thing was a lot of work. It's finally back together. The Go6100 was faulty, it would only start if i let it heat up a bit first. So i took it off and put a SPP100 instead. Temperatures are much better. 70-73C max as opposed to 120.

Summary:
Laptop came in with just the power LED lighting up and nothing else.

• Removed wired LAN chip as it was getting very hot.
• Found a little regulator that was getting very hot, found short on the output of that regulator, at the caps under the NF430 (MCP51) southbridge.
• Removed the NF430, short disappeared.
• Put in known good NF430, short was there again.
• Finally traced short to a very tiny ceramic cap.
• Replaced cap, short was cleared and board powered up.
• Found Northbridge Go6100 running extremely hot and laptop would only show video with it between certain temperatures.
• Replaced Go6100 with SPP100. This is possible as this notebook has dedicated graphics.
• Undervolted the 1.2v supply (NB/SB core) to 1.029v (should have been 1.2v, but it was actually 1.27v, the upper feedback resistor was different from the schematic!).
• Undervolted the GPU supply from 1.1v to 1.0v. The PWM controller used can't go any lower than 1v output.

And finally, it works without anything catching fire!

[Scootie]

Re: Asus F3T Northbridge burning

Those undervolting tehniques are amazging(for me ofc)!
Well done.

[Th3_uN1Qu3]

Re: Asus F3T Northbridge burning

It's nothing that amazing, it only involves changing ONE resistor in the power supply circuit for the desired chip... Of course, the tricky bit is figuring out WHICH resistor to change. I'll post snippets of the schematic later.

No pics of this one as all i was thinking of was "get it done already!". I'll play around with it till tomorrow, then i'll pack it in its box and mail it back to the owner on Monday.

[sparker1]

Re: Asus F3T Northbridge burning

Nice work again.

[mockingbird]

Re: Asus F3T Northbridge burning

Th3_uN1Qu3 - You are my master and my teacher

[orientalsniper]

Re: Asus F3T Northbridge burning

What machine do you have for BGA soldering? And what is your process for stenciling the bga chip?

[diif]

Re: Asus F3T Northbridge burning

Thanks Unique, I really like these threads of yours, insightful with your methods of fault finding and inspirational.

[Th3_uN1Qu3]

Re: Asus F3T Northbridge burning

What machine do you have for BGA soldering? And what is your process for stenciling the bga chip?

I built the "machine" myself. Nothing fancy. I'm using an old toaster for a preheater, i have attached a power control to it. For top heater, hot air station + BGA nozzles with mesh. I have posted it at some point.

I use direct heat stencils and Amtech flux, and temperature measurement is done by my two Uni-T multimeters. I have one probe near one corner of the BGA, on the board, and one probe on the BGA. I used to put it on top of the die but found out that having it on the substrate (the green part) is a better idea.

My success rate is higher than that of the guys who own ACHI.

[ktmmotocross]

Re: Asus F3T Northbridge burning

hahaha, have just like yours setup. but im using 200W halogen light as a preheater.
but i found that uni-t multimeter have big differences in temperature between it, even when i change the probes. And have big problems with board flexing, specially with big intel chips. do u using some kind of board clamp?
can u post some pic of that clamps?

[orientalsniper]

Re: Asus F3T Northbridge burning

I built the "machine" myself. Nothing fancy. I'm using an old toaster for a preheater, i have attached a power control to it. For top heater, hot air station + BGA nozzles with mesh. I have posted it at some point.

I use direct heat stencils and Amtech flux, and temperature measurement is done by my two Uni-T multimeters. I have one probe near one corner of the BGA, on the board, and one probe on the BGA. I used to put it on top of the die but found out that having it on the substrate (the green part) is a better idea.

My success rate is higher than that of the guys who own ACHI.

I also stencil with direct heat kit and Amtech flux (tried others, nothing beats the 4300-TF), I don't really have much problem in that department, how long does it take you to solder the balls on the chip?

Have you recorded your process for reballing? A lot of us could learn a thing or two from you.

[Th3_uN1Qu3]

Re: Asus F3T Northbridge burning

I thought about recording but i don't have a half-decent camera, also, a lot of the so-called pros will not appreciate the way i'm doing it at all, i'm sure i would receive plenty of badmouthing and bad publicity, and that is something i'd rather do without.