go to Devices Manager, look for keyboard entries (in 9370 there will be two of them; both drivers are supplied by Microsoft) and in the properties look at keyboard status description (textarea the bottom of the window)
browse through Windows Event manager logs to find something keyboard related
try to lift each keyboard key (watch out to not accidentally detach them) - maybe one of them is slightly jammed and blocks default input rate causing "character drops". If this will not help you can try the other way: press harder each keyboard key to "unstuck" it. Function keys are the most suspicious in such situation since "stuck key" like that do not enter visible character in the text fields.
keyboard connector might be loose - without notebook disassembly you may try to check this by gently shaking the device or trying to type in non standard position ie. upside down (I know this is weird but have no other idea how to check this without opening the device; you will perform this operation on your own responsibility ;] ). Any change in keyboard behavior will confirm that issue.