I have a few old t20s with similar issues:
Turn off the thinkpad, take out the battery, unplug the power.
Then press the power button for about 90 seconds.
Sometimes it'll work again right away, sometimes you have to let it
sit overnight (unplugged and w/o battery).
Not sure why it works
cb



On Jan 18, 8:27 pm, prc1 wrote:
I have an IBM Thinkpad A20m laptop (2628-4UU) that failed last evening
with the same symptoms that literally hundreds of others have reported
over the last few years. Mine had been running fine, but I went to
power it up and, once it got to the Windows desktop it froze. Powered
off, then tried powering on again. Unit comes on when power is
pressed (HD spins up, all lights flash on then go off except for
power, I can hear the CPU fan running). No POST, no boot, black
screen.

I replaced the CMOS battery, reseated everything, yada yada yada. The
thinkpads.com web forums list a possible cause as a failure of one (or
both) chips in the dc-dc power section on the mainboard. These are
the Analog Devices ADP3421JRU and ADP3410KRU ICs. This is supposedly
due to a design flaw. Some people also say to change three MOSFETs
(IRF-7811) as well. Some report success, others don't.

It seems to me that by simply replacing the chips you're not fixing
the problem. SOMETHING caused the chips to fail as there wasn't (to
my knowledge, anyway) a bad run of those chips. Bad capacitors in the
circuit, maybe? Bad resistors, diodes ...? People ARE apparently
fixing the boards, as dealers will sell you refurbished ones or will
fix your broken unit.

So, what's the secret? Which components are routinely replaced during
the course of one of these repair jobs?
** To respond, remove the crap from my addy... **