T20 did not boot on mains only...

[Msmax]

Had a T20 which did not like to switch on if only mains power was supplied. It booted fine with a fully charged battery. If mains power was supplied then the battery was not recharged.

Checked all the fuses on the MB, all OK.
Measured the voltage just after the first FET (direct below F2): 6V. Normally this should be 16V.

For a reason the FET was not switched on. The 16V must be available at the output of the FET if the mains power is connected without switching on the notebook.

I tried to follow the track from pin 4 (gate) without succes. So, I took a 560 ohm resistor and shorted pin4 to GND. The 16V was available again and everything works fine now for almost 2 days...
Even the battery is charged.

I would love to have a schematic of these mainboards...
It is very hard to follow tracks on multilayer boards.

IBM does not produce/repair these machines anymore, why don't they share the schematics?

Msmax

[SMA]

Indeed a very interesting solution you have created there.
That is what I would call creativity. Great.

Though a 600e is not necessesarily build the same way as a t20, they are out of the same family, so there might very well be semilarities.
So here is my story of a 600e that had the same problem as you have described.

I found a chip on the motherboard that was burned. It actually looked as though the chip had tried to bust out of its housing. It must have been very hot.
It was an LM324 chip. 14 legs. Cheap and easily obtainable. Just a simple quad opamp.
Only replaced that one chip and nothing else.
Afterwards, the machine were able to start from the main power. Though, I have to admit, that I never have tested whether the machine can charge a battery - will have to do that some day.

On the T21 motherboard that I have in front of me I can see that it also has a chip labeled 324A, so it would surprise me if a T20 does not have one too.

The 600e had its problem when I received it, so I do not know what has caused the problem, but my best gess is that it has been connected to an incompatible power adapter.
Most likely connected in a way so that the thinkpad has receive power with reverse polarity.

If I am right in thinking that it is reverse polarity that is causing this problem and it turns out to be a problem that can occur on the more modern machines, then I would certainly like to know this:

what does one do to apply power with reverse polarity to a thinkpad ?

It must be something simple that one can do without thinking too much about it. Kindof, by mistake.
I cannot think of a way of doing it with an ordinary ibm power adapter.

[rkawakami]

I found a chip on the motherboard that was burned. It actually looked as though the chip had tried to bust out of its housing. It must have been very hot.

You mean something like this on a T23 motherboard?

It must be something simple that one can do without thinking too much about it. Kindof, by mistake.
I cannot think of a way of doing it with an ordinary ibm power adapter.

It's possible that an over-voltage application could cause damage like this as most of the coaxial-type power plugs for laptops that I've seen are center positive. I'm not saying that it's a universal standard, just that for my Gateway, DFI and IBM laptops that's that way it has been.

Of course, if someone were to grab a plug that had a center negative wiring and a coax plug that fit into the Thinkpad, then that's your simple mistake. On my desk at home I have the IBM and Gateway power cords clearly labeled as to what laptop it is for, even though I use a docking station for the Gateway.

Another possible scenario is that somebody has attempted to fix a broken plug on a standard IBM adapter and doesn't know what the proper polarity is. Or perhaps they are trying to connect some other home-built power supply and didn't verify their wiring.

[SMA]

You mean something like this on a T23 motherboard?

Yes, something like that.

[tfflivemb2]

Hmmm...I wonder if this might be the cause of one of my T23s that won't charge the battery.....hmmmm

[vlyne]

Checked all the fuses on the MB, all OK.
Measured the voltage just after the first FET (direct below F2): 6V. Normally this should be 16V.Msmax

Let me get this straight. F2 is the transparent (thermal?) fuse and the FET is the 8-legged IC marked F7416 at the bottom? Pin 4 is the top left pin looking at the board in its "normal" orientation? If F2 is a thermal fuse, I wonder what the thresholds are - it could be going out of wack??
Cheers