various Laptop models no response to power button

[invo]

Hello All

Ive been asked to look at various W8.1 & W10 laptops this year including 3 x HP models. The other system I have seen the issue on was a Lenovo. The issue in all cases is remarkably similar. Each one was working fine and then each one for reasons unknown refused to boot. I have tested with replacement HDD's, bootable media, RAM swaps, Power Button assembly swaps, replacement Power Adapters, CMOS battery and DC Jacks.

In all cases the systems have simply refused to boot no matter what changes have been made to the hardware and in each case a replacement system has had to be purchased. I have stripped the systems and visually inspected each for worn/blown components with no joy.

Circuit tracing has not shown up any issue (that I can find) on the power circuit indeed on at least two full voltage was getting to the board via the DC connect cable.

I am stumped, can anyone suggest what the issue is/maybe how do I prove it and what can be done about it?

TIA

[Huffer]

You have gone further than I would. You have a series of dead motherboards I would guess. And dead by something other than a burned or obviously visibly damaged capacitor/chip. Happens.