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Old 02-29-2016, 12:20 PM   #1
ChaosLegionnaire
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Default curious case of an overheating intel lan chip

i recently got an abit ic7-g max ii off trashbay. all of the board's slots, connectors etc. all worked fine except for the lan. the board uses intel's csa gigabit lan chip (intel pro 1000 ct).

i noticed that the lan works on a cold boot. but as the board heated up, the lan started to cut out and the activity and speed leds kept turning on and off as if someone kept unplugging and plugging the cable. note that this is not the normal blinking when there is network activity.

on the lan connection software, it also kept cycling between "connection active" and "unplugged". it also does this when idling at the bios and in windows and linux, so its not the drivers. i changed many different lan cables and also checked the pins on the ethernet connector. no damaged or tarnished pins were found. there were also no obvious signs of scorching/heat damage or physically damaged components around the lan chip.

next, i touched the lan chip and noticed it was quite hot to the touch. i estimate the temp to be around 55-60C. for some strange reason, when i put my finger on the lan chip, it seems to start working again. but when i put my finger away, it cuts out again and starts blinking.

at this point, im wondering if its a cracked solder joint or an overheating chip. i've never heard of cracked solder joints working when cold and failing when hot. so i went with the chip somehow overheating. could it be a bad mosfet beside the chip? i measured the voltage on the mosfet with a multimeter. the source voltage was 3.25v, the gate voltage was 1.2v and the drain voltage was 2.4-2.6v. doesnt look like a leaky mosfet to me. also doesnt look like excessive voltage causing the chip to overheat.

so i slapped a small aluminium bga ram heatsink with 3m thermal tape on the lan chip and blew two 80mm fans across the pci slot area. the lan chip now remains cool to the touch and no longer cuts out during heavy network activity. it should also be noted that the malfunctioning and overheating lan chip doesnt hold up the system from booting or anything. bios detects it fine and assigns it an irq. it just keeps working intermittently when it gets hot.

being a person with a medical background, im curious as to the root cause of why the intel csa lan chip is overheating. i have an msi 875p neo2 board with the same lan chip as the abit ic7-g but it has never had any problems with overheating. neither does it require a heatsink to work. any idea why the intel lan chip on my ic7-g is an overheating turd? i fear putting a heatsink on the overheating lan chip only tackles the symptom of the problem and not the root cause of the problem: why is the lan chip overheating in the first place? bad mosfet? lightning strike damage or high voltage surge over the lan interface from the previous owner? anybody experienced bga failure whereby things work when cold but not when hot?
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Old 02-29-2016, 02:56 PM   #2
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Default Re: curious case of an overheating intel lan chip

There can be an internal short in the chip which does not affect its functionality too much. I've seen that happen before. If it works with the heatsink, let it be and use it while it lasts.
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Old 02-29-2016, 07:55 PM   #3
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Default Re: curious case of an overheating intel lan chip

I have had microcontrollers with ESD damage overheat in a similar manner. They operate normally while running very hot, but cut out occasionally as the logic stops working properly at high temperatures. This causes the IO pins to be cycled (usually one is stuck low shorted), turning off the bad IO, resetting the MCU and restarting the process.

The most likely cause is one of the pairs on the ethernet output is down. I believe gigabit ethernet can operate in a degraded state with only 2/4 pairs active (I'm not sure if it drops to 100Mbps or if it just switches to half-duplex.)
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Old 03-02-2016, 08:50 PM   #4
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Default Re: curious case of an overheating intel lan chip

probably wounded by lightning.i have replaced plenty of lan chips and the customer always reported that it died after a storm.
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Old 03-02-2016, 10:21 PM   #5
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Default Re: curious case of an overheating intel lan chip

It possible it can be a high resistance short around 20 ohms or more that when the chip heats up will grow and expand and cause a direct short. This could be a solder short and when you press on the chip the board could flex enough to get rid of the short and when you let your finger off it could come together again. In cold crack solder there may be arching that would heat up the solder joint. I would think with all the current protection in these devices it would shut down the machine. Cold solder usually works opposite as it heats up as it expands and make contact. Any type of static discharge that is high enough could also cause a problem that would pass initial test when new and fail 3 months latter.

Last edited by keeney123; 03-02-2016 at 10:24 PM..
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Old 03-20-2017, 11:33 PM   #6
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Default Re: curious case of an overheating intel lan chip

just an update on the issue. it seems now that the lan chip refuses to work at gigabit ethernet speeds anymore. it will only run at fast ethernet 100mbps speeds without cutting out intermittently. so i have to set it in the device manager lan driver properties page to force it to run at 100mbps full duplex speed.

when at that speed, the lan chip heatsink is rather cool to the touch but at gigabit ethernet speeds it heats up quite a bit even with the heatsink and fan blowing at it. so i guess like tom66 and kc8adu said, the core logic in the lan chip is damaged somehow most likely by an esd lightning strike, so it is incapable of operating properly at its maximum speed of gigabit ethernet. "downclocking" the lan chip to run at fast ethernet 100mbps speeds seems to relieve a lot of the stress on the core logic of the lan chip, so it works much cooler and runs properly again with no issue. im fine with it at that speed anyhow, 100mbps is enuff throughput for me when gaming. i dont really download pr0n that much anymore, so i dont need the throughput of gigabit ethernet.

ah well, im praying it stays like that forever and doesnt worsen anymore. its no fun using wireless. lag spikes too much especially when gaming and all wireless channels have at least 2-3 ppl on the same channel. thats what u get for living in a built up urban environment! lol!
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Old 03-21-2017, 06:14 PM   #7
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Default Re: curious case of an overheating intel lan chip

It's desktop mobo. You can install PCI Ethernet card. This will cost you 5 Euro. And generally solves your problem. Realtek for 5 EUR.
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Old 10-10-2018, 11:25 AM   #8
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Default Re: curious case of an overheating intel lan chip

well, i think i figured out the behaviour of this screwed lan chip finally... what happens is that on a cold boot, it seems to work fine initially at 100 mbps link speed for about 5 mins. then as it heats up a bit, it cuts out. then i have to switch the link speed down to 10 mbps which brings it back and i have to leave it at that speed for about 30 mins in order for it to continue working normally. then switch the link speed back up to 100 mbps and it continues to work flawlessly after that.

well, i guess this chip is suffering from multiple symptoms. both a combination of bad bga and lightning esd damage from its previous owner. looks like i now need to have a "daily routine" as described above for this board lol! talking about ocd! hahaha!

anyway, here's some pics of the lan chip on the mobo with the heatsink mod.
Attached Images
File Type: jpg intel lan chip heatsink mod 1.jpg (175.6 KB, 16 views)
File Type: jpg intel lan chip heatsink mod 2.jpg (107.8 KB, 14 views)
File Type: jpg intel lan chip heatsink mod 3.jpg (414.6 KB, 21 views)
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Old 10-16-2018, 08:48 PM   #9
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Default Re: curious case of an overheating intel lan chip

Quote:
Originally Posted by ChaosLegionnaire View Post
well, i think i figured out the behaviour of this screwed lan chip finally... what happens is that on a cold boot, it seems to work fine initially at 100 mbps link speed for about 5 mins. then as it heats up a bit, it cuts out. then i have to switch the link speed down to 10 mbps which brings it back and i have to leave it at that speed for about 30 mins in order for it to continue working normally. then switch the link speed back up to 100 mbps and it continues to work flawlessly after that.

well, i guess this chip is suffering from multiple symptoms. both a combination of bad bga and lightning esd damage from its previous owner. looks like i now need to have a "daily routine" as described above for this board lol! talking about ocd! hahaha!

anyway, here's some pics of the lan chip on the mobo with the heatsink mod.
consider sourcing the chip for replacement for long run...

i fixed up a print server .... suspected blown by lightning by replacing the realtek chip...

but need hot air rework station
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Old 10-17-2018, 06:17 AM   #10
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Default Re: curious case of an overheating intel lan chip

even with a rework station, pulling the chip is going to be a very tricky affair as its surrounded on all four sides by mlccs and resistors. melting the bga solder under the lan chip would also melt the solder of the surrounding mlccs and resistors causing them to move, come off their pads or short together. will have to watch it before applying power!
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Old 10-17-2018, 06:54 AM   #11
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Default Re: curious case of an overheating intel lan chip

^^ It's really a lot less tricky than you make it to be. For a BGA this size, a simple hot air rework station, soldering iron and braid should suffice for replacement.
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