T42 Troubleshooting Bad Motherboard

[Paul Pennington]

One of my T42's seems to have died suddenly. It's a 2373-JTU, a 14" XGA 1.7 MHz. When I went to turn it on, I noticed the green charging light was not on, and pushing the power button had no effect. I tried a known good power supply with the same result. At some point in my testing, the computer came on and went through the normal boot screens for about 30 seconds, but then cut off completely with no lights showing before the boot process completed. This happened about three times, stopping at the same point each time. Now, it's back to not coming on at all.

I removed the battery, PC WiFi card, hard drive, and bottom memory module, but no change. It appears some component on the motherboard is drawing so much current it's shutting down the power supply.

Anything else I should try before I start looking for a replacement motherboard (FRU 27K9980)?

[tim S]

Make sure the fan is working correctly.

Tim S

[poshgeordie]

If the board came on a couple of times it's probably not fuses.

Obvious thing to check is that the CPU is properly clamped into it's holder - if it's not it causes the laptop to fire up and immediately shut down again (slightly different to what you're reporting I know).

Try pressing down hard on the Southbridge and powering up. A badly unsoldered SB will cause nothing to happen and in these cases needs a reball (not reflow). Seen this quite a lot.

I've got two boards here where you press on the components above the fan and it then starts up. I've never got to the bottom of which component(s) have become unsoldered to cause this but do wonder if there's a through hole between the top and bottom PCB's on the motherboard which has broken.

If you have a test meter, check if you're getting 16V on the 4 wire DC plug in the top left corner of the motherboard next to the LCD connector. If you are then it's not the Power Supply.

You don't mention if it works on battery, but I guess not.

[Paul Pennington]

Thanks for the replies.

As I said, it's completely dead, no fan, no lights, nobody home.

I checked both power supplies I was using for testing, and both are putting out the normal 16-odd volts. I also have an AC ammeter, and it measured 11 mA AC on the input to the power supply alone, going up to 12 mA when plugged in to the computer. So, I need to revise my guess that there was a short on the motherboard drawing excess current -- it must be an open circuit soon after the input.

Looks like it's time to replace the motherboard.

[ajkula66]

Remove all the RAM and power the laptop on. Does it beep?

[Paul Pennington]

Remove all the RAM and power the laptop on. Does it beep?

No

[ajkula66]

Then it's replacement time I'm sorry to say.

I should have a proper planar for your machine by the end of the week, PM me if you can hold out that long...

Good luck.

[Paul Pennington]

It was a bad motherboard. I scored a replacement on eBay for $30.50, including shipping. Swapped it in this afternoon and evening, and everything is working fine now. I replaced the original 27K9980 with a 93P4156, just to match my other two. Booted right up from the original hard disk.

I'd never torn down a T42 further than the palmrest. Replacing the motherboard is a PITA, but all went well with some careful "screw management". The T42 is actually easier to work on than some of the older ThinkPads.

[ajkula66]

Paul Pennington wrote:

Replacing the motherboard is a PITA, but all went well with some careful "screw management".

Not everyone is as careful as you. I've just received a near-mint T43p that was killed by a (longer) screw sent right through the motherboard...

Anyway, glad to hear that you've found a great deal and that it worked for you. Enjoy!

[RealBlackStuff]

In view of our upcoming motherboard depot, perhaps you's be willing to donate your old mobo to the cause?
See this thread from Harryc's post onwards: BEWARE of Superior Reball and Rework for GPU reballing / fix
PM me for details if interested.
Thx in advance.

[Paul Pennington]

RBS:

I didn't realize that zombie thread from 2009 had come back to life You, or anyone else, is welcome to this board for the cost of postage, but I don't think it would be a good candidate for a repair. It doesn't display the symptoms of a graphics problem. This is the same board that gave me so much trouble earlier with an intermittant connection to the mini-PCI socket where the wireless card lives. So with two problems, you may want to pass on this one.

[RealBlackStuff]

Thanks, you may be right.
Before you dump it, keep the yellow power connector, worth a few on eBay.