What is the exact role of NVRAM ? Isn't RAM supposed to be a volatile kind of memory ?


Is it something that is known to happen with old HDDs ? It's strange in the sense that the fuse is supposed to protect, but if that is indeed the case it would be the direct cause of the failure... “Same thing that helps you live can kill you in the end”, as Neil Young sings.
Or could it have been a short circuit due to the way the drive was plugged ? I'm not certain, but when the failure happened it may have been lying directly on top of a 3.5" HDD (itself unplugged), plugged through a SATA-to-USB board with no plastic protection, which I realize now might be a very bad idea...
Bridging means simply soldering a small wire on each side, correct ? Is it risky even if the power supply is perfectly stable ? (I do have a UPS.)
According to “Spildit”, the odds of success for this kind of repair procedure are low with Hitachi drives in particular, do you have similar experiences ?
As for replacing that fuse, where can I find one, short of getting a similar PCB just for that purpose ? I doubt I could find that tiny thing in a regular electronic shop.
And as for a PCB with a matching firmware, isn't that a fool's errand, based on the “adaptive” data which supposedly is also embedded in the ROM code ?

Thanks again, and sorry for those long delays between replies, as I have more urgent matters to deal with right now (cat related in particular – my poor lady has had breast cancer for three years, and it's getting really hard to find a fix at this point...).