T420 won't power on, stuck on blinking green light (solved)

[excal32]

I followed the manual at http://download.lenovo.com/ibmdl/pub/pc ... 0i_hmm.pdf to a "t".

This is not my first time doing a full disassembly/reassembly of a laptop.

However after putting it back together, when inserting battery or AC, the green power light on the keyboard comes on and seems to "pulse" in 1 second intervals.

I've gone mad trying to double check all my work and can't find anything I messed up. Why would it be doing this?

I can't find an answer searching here or Google at all. I did make sure to get an intel graphics motherboard so that should all be fine...

No fan spinup or anything, the power button does not respond to being pushed either, just goes green and "blinks", or it starts up just long enough for me to see the "Thinkpad" logo before it shuts off again.

[TPFanatic]

I've done full reassembly of Z60m and T500.

I've found that after removing the CMOS battery from a motherboard of the Lenovo era, the board will automatically turn on with AC power and power cycle twice. After power cycling twice, it will work as normal.

....I used this method to boot a machine without a keyboard, actually, to test the screen. Remove and reseated CMOS battery, then plugged it in and it booted by itself.

Perhaps try letting it pulse its light, indicative of power cycling, a few times and it might begin working properly

[excal32]

At this point the screen will come on for just a second and then it dies again. New motherboard bad or did i screw something up?

cmos is plugged back in BTW.

If I press the power button, a couple lights come on, it goes dead for a few seconds, tries to start again, and then same thing. never seen this before. It's actually the same behavior as if i have no battery (normal or CMOS) in and plug in power, same thing happens.

[TPFanatic]

Well... I don't know if that's normal behavior. I don't recall if the screens ever flashed during my machines' power cycling. I can pull my CMOS battery and analyze in better detail the details of revival.

My bad. Okay, now I read your posts in better detail and I think, it showing the Thinkpad logo, then shutting off doesn't sound right at all.

[excal32]

Well... I don't know if that's normal behavior. I don't recall if the screens ever flashed during my machines' power cycling. I can pull my CMOS battery and analyze in better detail the details of revival.

My bad. Okay, now I read your posts in better detail and I think, it showing the Thinkpad logo, then shutting off doesn't sound right at all.

Even weirder. Everything works... if they keyboard isn't plugged in.

Is it really actually possible the T420 keyboard is screwing it all up?!

I will make a new thread for this...

[jaspen-meyer]

Did you put the screws in the right holes? Long screws in the wrong holes can cause trouble.

[excal32]

Did you put the screws in the right holes? Long screws in the wrong holes can cause trouble.

It turned out that my keyboard was the culprit this whole time. I swapped in a replacement motherboard as one was only $20, and a brand new keyboard was $35, so for $55 my T420 works perfectly again

Not even sure if I needed the motherboard replacement? It could have been the keyboard this whole time. Either way, the feeling of a fresh new keyboard on my old T420 is great if nothing else!