Fixing a T43p / T4x mainboard, 2nd update: broken again

[DarkMark]

Hello,
I have following problem:

I bought a used T43p sytemboard from ebay. It was up as defect and sold "as is". I got it because I thought it was worth a try to repair it.

Wenn I got it I first took out the fan to put a processor in an try it out.
It still had the original processor installed, so lucky me.

I then put it in a minidock to use it's power button to try it out. Nothing happend. After reading in a topic in a different thread about a TP running on battery but not AC I put a battery in and it fired up, but needed to go to bios and had a supervisor password set. I contacted the seller and he gave it to me.

So I've now got a mainboard that runs on battery but not on AC.
The first thing that struck me was one IC that had a melted housing and had singed the insulating plastic under the modem daughter card. It has " tpc 8014 (6121)" writen on it. Searching the forum only came up with one topic with the chip mentioned.

So finally here comes my question:

Do you think this burnt chip can cause not booting from AC?

Does anyone know where to buy one?

Thank you for any help.

Mark

[rkawakami]

Does it look something like this:

http://www.rkawakami.net/ibm_t2x/let.jpg

If so, then it's probably an N-channel MOSFET (Metal Oxide Semiconductor Field Effect Transistor) as described in this datasheet:

http://www.ortodoxism.ro/datasheets/toshiba/2842.pdf

You can find them in single-unit quantities from:

http://www.mouser.com/search/refine.aspx?Ntt=tpc8014

edit: Oh, just noticed you are in Germany. Don't know if Mouser.com ships international. You may want to try a European distributor of electronic components. And yes, something like this can prevent power up. It basically is an electronic "switch" which passes current. The one in the picture above came from a T23 motherboard. It actually had a real neat orange glow, like an LED, for a couple of seconds. After which it left behind a small crater in the package and the release of some "magic smoke" . Also, replacing this component may not fix the problem as it might burn up again.

edit2: Found this on mouser.com: International Customers.

[DarkMark]

Does it look something like this:

http://www.rkawakami.net/ibm_t2x/let.jpg

Yes looks very similar.

I had already looked at the datasheet, and it said something about li-poly batteries so I wasn't sure if it had to do with the AC circuit.
I'll give it a try first before I look any further.
At least it's a rather large part so that soldering isn't difficult.

Interesting link, thank you.

The items shown are cross references, do you think they would work?

If so I can use the part numbers of those to see if I can source them over here.

Thank you very much for the help.

[DarkMark]

Sorry for the double post.

Ray (or anyone else),

do you think this might work?
this
I looked around a bit, and that was the only thing similar I could find.

[BillP]

That looks like a good substitution. I'd try it.

[DarkMark]

*Update and new Question below*

After looking around for a substitute part I thought it would be better to get a whole mainboard, so then I've got more spare parts in case others where broken as well.

I then bought a defective t40-motherboard from ebay and swapped the mosfet.

The problem didn't go away though, so I looked at the circuit around the jack and noticed a fuse.(or what I think is a fuse).

I measured it with a multimeter and it is not conductive. I then messured the one on the spare mainboard and it was conductive.
But when I tried to solder it of, it broke a bit and then I lost it.

Question:

Now I need to know what value the fuse has so I can replace it.

Thank you.

[DarkMark]

Update for anyone interrested:

I went by a small local electronics shop, bought a 7A THD mini-fuse and bridged the broken fuse on the mainboard without taking the old one off.

I then put the board on the minidock and it fired straight up without battery, I had it running a bit and it seems ok.

All I've got to fix now are some minor problems since the board is in an R51 case.

[DarkMark]

Bump to my thread because the problem still remains.

The problem before was that one of the mosfets next to the fuse of the ac connector burnt and took the fuse with it. I replaced both and that was 3 months ago.

The above mentioned mosfet burnt again, this time even worse, it got so hot the legs turned blue the solder melted and it became totally disconected wich made me think of:

. Also, replacing this component may not fix the problem as it might burn up again.

Any ideas what might cause the death of the mosfet?

[zdriver]

Assuming you still had the T40 substituted component in when it died - the 43p board probably has a higher current demand compared to the T40 - graphics, processor, etc.
The T40 mosfet was underrated and finally died due to the high current draw and heat.
Other than that, tracking down a fault on the board causing the problem is difficult without schematics.

[DarkMark]

Thank you, for the answer,
but the component I replaced with was not a substitute but exactly the same. The two mainboards are very similar.

And yes tracking down the problem will be very difficult, that's why I was hoping for some ideas.

[sjthinkpader]

The largest energy user in a Thinkpad are: CPU, GPU, battery and the LCD. If something is using enough current to fry a MOSFET, it would run hot.

So replace the MOSFET again and touch the various components to see what is running hot. An IR thermometer would be best but finger will work too. Just be careful not to burn it.