This is a video demonstration i made while i replaced the motherboard of my Toshiba Qosmio x70, Ive also shown how to add extra ram or add an SSD, as the laptop can carry 3 drives, via 2 sata ports plus an M2 on the underside of the motherboard.
Here are some important notes from the video i cut down, edited out, or are just important;
When buying a motherboard from a 3rd party seller, they will be really annoying about making sure they sell you exactly the right motherboard, the place i bought this one from refused to sell to me the first time because apparently the "model did not match", they needed a bunch of specs and photos, and thing is, literally 100 different serial numbers exist for the exact same computer (laptop serial number not motherboard serial), depending on where its sold and what parts it has. Now this is my personal opinion, and just for this specific laptop, but, all you need to do is make sure that the motherboard serial number is correct, the revision number (e.g rev H), and that the motherboard has a graphics card slot since apparently some exist out there without GPU slots. If the seller can guarantee their listing photos are accurate, then thats all you need.
Also, this is speculation but the motherboard revision number should be the latest one, H or later, if your board is of an earlier model that might explain why it failed. Some x70s exist which overheat and brick themselves, some come out, others dont.
More info, asuming your local toshiba parts distributor still exists now, remember that while a motherboard may cost $500 there vs $100-300 from a 3rd party, the toshiba supplied (or in my case EMPR) motherboard will come with a 1 year warranty.
Another thing. To gain access to the keyboard you have to remove EVERYTHING, i asume some screws hold down a sheet of plastic that holds the keyboard in place under the motherboard somewhere. The keyboard sticks out through holds in a solid shell, you can only replace the keyboard by going in from behind, the top doesnt pop out like in some other laptops.
Lastly, to anyone using their x70 with a second monitor, read this blog
The long short of it is that an aging CCFL based monitor can fry your motherboard, and either the wacom cintiq 24HD was particularly bad, or the qosmio x70 is particularly vulnerable, but in most all failing/aging CCFL lit monitors, they will electrify the common ground shared between the laptop and monitor.
-Edit- i included some important photos to show the mSATA slot and the underside of the motherboard in general. Sorry i dont have a good picture of the SSD but ive included a cropped still from the video.