T41 motherboard short circuit

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Rrrr7 · #1 Post by **Rrrr7** » Sat Jul 27, 2013 9:26 pm

Hello guys, this is my first post here !

I happen to have a T41 2373 model wich a few months ago got its mobo fried, I think because of the charger used. I got another mobo from ebay and a new charger and it worked fine for a few days but then suddenly it died. There is no LED, no charging, no fan powering on, absolutely nothing happens with or without the battery or charger plugged in. I dissasembled the laptop, removed the motherboard and all of its components and figured out the the fuse near the charging port is blown. I replaced the fuse but now when I plug the charger it immediately shuts down and up in a continous cycle. Somewhere on the mobo there is a short circuit. By curiosity I checked he old fried mobo and guess what ? It has the blown fuse also, and it shorts out the charger as well.

Is there a known component that cause this on T41s ? How do I track down the faulty component causing the short ? Is it worth it to fix it ?
I really don't want to throw this laptop in the trash bin, I hope I can fix it.

Thanks

#2 Post by **RealBlackStuff** » Sun Jul 28, 2013 1:54 am

Welcome to the forum.
Did you buy a genuine IBM or Lenovo 16V/72W charger?

Rrrr7 · #3 Post by **Rrrr7** » Sun Jul 28, 2013 8:38 am

RealBlackStuff wrote:Welcome to the forum.
Did you buy a genuine IBM or Lenovo 16V/72W charger?

Yes.

Rrrr7 · #4 Post by **Rrrr7** » Sun Jul 28, 2013 6:51 pm

I've checked for components damage visually, found none, but I did notice that the component (transistor ?) marked in green in the pic attached gets hot very quickly, almost burning my finger in just a few seconds.
What is that ? Could that be the faulty component ?

http://i.imgur.com/CBntWMc.jpg

Admin edit: Removed HUGE inline image. When posting images please keep them < 50KB and put an *PIC* warning in the original subject line.

#5 Post by **rkawakami** » Sun Jul 28, 2013 7:04 pm

Most likely that 8-leaded IC is a MOSFET. It's a type of transistor typically used in power supply switching/control circuits.

Rrrr7 · #6 Post by **Rrrr7** » Sun Jul 28, 2013 7:11 pm

rkawakami wrote:Most likely that 8-leaded IC is a MOSFET. It's a type of transistor typically used in power supply switching/control circuits.

Can that be changed ? Is it worth it ?

#7 Post by **rkawakami** » Sun Jul 28, 2013 7:46 pm

Yes, but it can be difficult if you don't have the proper desoldering / soldering tools. As to whether or not it's worth it, that's debatable.

The F2 fuse between that MOSFET and the white DC input connector is what is supposed to protect the system from any power input problems. If that's the fuse you replaced, then that could mean the MOSFET is defective, which caused the excessive amount of current to flow and in turn blew out the fuse. It's also entirely possible that the MOSFET is (still) working properly but that a short elsewhere in the power input circuit is the real problem. You could replace the MOSFET for probably a few $$ or €€ and hope for the best.

The method I would use to remove and replace the MOSFET is the following:

- Before removing the MOSFET, make note of the location of pin 1. That's the pin closest to the white "o" near one of the corners of the device. From the photo, that seems to be the upper right.
- Using a pair of very small diagonal cutters, cut each of the 8 legs of the MOSFET.
- This will enable you to remove the body of the MOSFET but leaves tiny pieces of each leg still soldered to the motherboard.
- Using a low-power soldering iron (25W or so) and the finest tip you can get for it, heat up each leg one at a time and use a vacuum solder sucker to remove the leg and excess solder. Do NOT use too much heat from the iron or you could damage the metal pads on the motherboard. You can clean up the pads using solder wick.
- Put the replacement MOSFET over the eight pads, making sure pin 1 is in the correct position and using the thinnest solder (28 gauge or so), solder one leg at a time. It may help to have somebody keep the MOSFET from moving (push down on it using a screwdriver) while you apply the solder.

Rrrr7 · #8 Post by **Rrrr7** » Sun Jul 28, 2013 9:22 pm

Thank you !
I will take the mobo to a friend wich has the skills and experience to do it and see if we can get the board fixed.
I wonder though, what could cause the same damage to two boards in a row ? As I mentioned, the first board has the same issue.

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Rrrr7 · #9 Post by **Rrrr7** » Mon Jul 29, 2013 7:47 pm

Anyone has any ideea where to buy the Toshiba TPC8014 mosfet from ? I can't seem to find it with shipping to Europe.

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