T42p power problem only on AC

[rtpnc6]

My 7 year old T42p (2373-KTU) system is now experiencing sudden shutdowns when connected to external power. This happens regardless of whether it is in the docking station or connected to the power brick. The system will run reliably on the battery, but when I connect it to the power brick, the system will shutdown within 5 minutes w/o any messages. The fan is running properly and the CPU and GPU temps are below 50 degrees C.

I changed the CMOS battery to see if there was any problem with that, but the symptoms remained. The system will charge the main battery to 100% w/o any issue as long as the unit is not turned on. It almost sounds like a thermal problem, but I can run TPfancontrol and see that everything is within limits. When the problem happens, the unit tries to reboot, but is unsuccessful (screen is also blank during those attempts).

Any ideas? I'm stumped. I've inserted my XP system HDD back (I was running Vista Ultimate) to see if anything would change with a different OS, but the problem persists.

[Harryc]

Check the output of the AC adapter with a multimeter...should be 16v DC.

[rtpnc6]

16.2v on both power bricks

[SreeKumar]

16.2v on both power bricks

1) Even if the OP is 16.2 Vdc it may not have the prescribed current ie 90W on load. Both your Power supplies can't be defective, also.
2) So, the next in line to suspect is your ext. PS socket. These get loose and the center pin
may wobble due age and constant pulg ins, plug outs... ext. PS socket has also exhibitted shorting internally when pulgged in. (mechanical)
3) Above inference is assumed because T42 works with built in PS. (Battery)
Sree...
06/08/2011

[lukee]

Check this out:
http://forum.thinkpads.com/viewtopic.ph ... 1&start=30,
or directly this:
http://mayohardware.blogspot.com/2009/0 ... d-t40.html

[rtpnc6]

The power bricks for the T42 are 72 W, not 90W. Also, the condition occurs in the full docking station as well which has its own builtin power supply. The second post is most likely the issue (MOSFET). I'm not too keen on completely disassembling the system just to solder a part on the planar and not to know if anything else is kaput until I reassemble it. Looks like it's going back into the shipping box in the closet to begin a long sleep.

Thanks for the replies.

[RealBlackStuff]

Putting it into a long sleep is not going to solve the problem...
You do yourself an disservice that way!

Using the HMM, it takes only a few minutes to dismantle the T42 far enough to access those 2 items (MOSFET and fuse).
You don't even have to take the mobo out of the base.

Another thing to try: if you have it open anyway, remove the wifi card. Under it you will find a big Intel chip, the Southbridge.
Put and keep pressure on that (try several corners) and see if she now boots.
If yes, the Southbridge needs to be reballed. For more info, see The Board Room my signature.

[rtpnc6]

I was under the impression that I needed to remove the mobo in order to remove the fuse and chip (the fuse is OK, btw). So, how can I remove the chip and resolder w/o proper equipment. Anyone out there who can tackle the task? I would only want the current board repaired and not exchanged.

Thanks for listening.

[RealBlackStuff]

A 15W small soldering iron and desoldering wick from Ratshack is all you need.