We have a cheap, Aldi TV PVR here ... a 1TB drive being used inside. Unfortunately, the programming done to make it all work is dreadful, and it's extremely clumsy, and slow in operation. Over time more and more clips added, and it's been switched off at "the wrong time" so often that the poor thing is completely confused - the files are a mess, and the box finally became unusable to record, and play.
So, fixit time! Nothing inside just about; small power supply, drive, and circuit board the size of a smart phone - removed the HDD, plugged it into a general mounting kit with USB - and had a look. Files all still there, but huge amount of stuff that was supposedly deleted, but also still there - no wonder it was so slow ...
Now, the idea is to backup all the wanted clips, and clean up the drive - there's definitely disk errors, Windows and CHKDSK say so. Started copying the most important files, and problem one: the operation slows to a impossibly slow crawl depending on whether it's full moon or not, completely erratic in the speed. Googling, and this is Yet Another Windows Nightmare - this copying speed issue is driving people batty, and there are a 100 reasons, and possibly another 100 answers on how to "fix it". Part of it could be due to fragmenting - it uses the exFAT file system, which is not as robust as NTFS. Anyway, recovering all the important files will take weeks, with this speed issue.
Changing tack, will try to sort the file system errors - at first I wasn't sure whether CHKDSK was actually doing anything, there's zero progress indicators, and many operations freeze when trying to talk to the drive; I'm discovering all the recent disk utilities as I investigate things - and there's some good stuff out there. Finally convinced myself that CHKDSK was working, and now seeing if that program has enough grunt to work it out.