what else fixdisk runs (other than fsck)
It taps into the SMART stuff on the HDD itself, enabling sector re-allocation or whatever self-repair the HDD couldn't achieve while still "live". That much has been dealt with.
fixdisk also has "knowledge" of the file system structure (which you would otherwise have to specify in
fsck commands), and handles use of a swap file (virtual memory) when necessary, by only taking portions of the file system off-line when possible.
better to do fsck on a Linux box?
The HDR-FOX has a low-power processor and limited RAM. The use of a swap file also slows things down, is not always possible (it depends on some of the HDD being available to use!), or might not be big enough.
Is it worth doing one (or more) fixdisks!?
I suspect the out-of-memory problem is preventing any further progress from being made.
Has this type of problem (disk H/W OK, fixdisk unable to correct FS) been seen before?
Probably, but I don't recall and it's certainly unusual. Nonetheless, the actual HDD appears to be in good health hardware-wise so it is worth pursuing reinstatement rather than replacement.
If you have little of value stored on the HDD I recommend simply reformatting through the menus. If there is little enough, you could copy it to USB first. Anything more and it would be a time-saver to connect the HDD to a PC for file transfers, BUT USE LINUX (because the Ext3 file system is not compatible with WIndows).
i am not familiar on exactly how NVM is used or if it is checked so if I changed the HDD what are the chances the NVM is deteriorating and any new install will not be successful?
Nothing to do with it.
the box seems OK ATM and I get the impression the picture is clearer!
"Clearer"??? HDD problems can result in picture break-up or other glitches, but certainly has no effect on the actual quality of the picture data. I suspect you have simply altered the resolution of the HDMI output (on the V-FORMAT button).