should I not have combined [parts from different T420s?

[thisway]

I had two T420s with different problems. One was behaving so erratically that I suspected the CPU was failing. On the other, the screen had failed. I combined the useful parts of each--the good screen with the good CPU. I did this knowing that they were different T420 models. I convinced myself it probably wouldn't matter. It's academic now, because the frankensteined T420 just died on me. Shut off and won't start again, and the back lights don't register that the PSU is plugged in. Oh, well: these used T4xx laptops don't last forever. I've been through this before.

It's just that in retrospect, I wonder if I should have known that combining parts from laptops not quite identical was a bad idea. THe internal wireless card in the combined T420 never worked well, connected to the wires coming from the screen that I transplanted. I even tried the wireless cards from both T420s, and replaced the wireless card once (with another T420 card, of course). Could it be that the real problem was never the wireless card, but trying to connect it to a screen from a slightly different T420?

[mikemex]

Modern components have some ESD protections but it's still possible to damage things with careless handling. I've killed some stuff over the years by just swapping things around like you did. I used to have a couple of quite rare desktop Pentium M motherboards, and I killed one when I decided I wanted the case case it was installed into...

I've always told people: pick the parts from the PCB, never from the electric leads. Try to discharge yourself before touching anything. Always treat stuff thinking it's fragile, both physically and electrically. Don't do unnecessary stuff. You know, like the Chinese say: if it isn't broken don't touch it.

[Gonzaleitor]

Nah, I do this all the time... Maybe something went wrong cause you connected something in an sketchy manner. I wouldn't declare it dead yet, just try to reassembly with the parts you have.

[TPFanatic]

Coincidentally i had a rough start with my own T420 collection, I had bits and pieces of them from parts lots and wanted to build one up to flip. I did encounter random failures and from that felt they were unreliable, never managed to sell one, but it was just bad luck. Eventually around 2019 I had two working machines, I did the QHD and FHD mods on them, and they still work to this day albeit they’re no longer regularly used. I dailyd an i5 T420 through til the end of 2022, it’s one of the most solid feeling and well constructed ThinkPads in my opinion alongside the P71 and the A30. With the QHD mod it was the best classic ThinkPad i ever owned.

[axur-delmeria]

It's a laptop that's over a decade old. At that age all bets are off. My X220 died late last year.