You've run down a few trouble shooting steps I would have done on most hard drives, internal and external.
However, I am not sure what you mean by 'replaced the USB chip with another HDD'. The HDD is not a USB chip.
If you mean you replaced the internal HDD unit in the external enclosure with another HDD unit, then the answer seems evident enough.
What you have done seems to rule out a damaged connector, damaged power jack, damaged cables (Its not impossible however it IS highly improbable at this point).
When you have the 'damaged' HDD in the enclosure does the drive 'feel' like it is spinning up? You can generally feel/sense a resonance hum the platters inside spin/spin up. If you lifted the enclosure (not really suggested) you might also feel a slight shift in the enclosure, especially when you start it up.
Without running seatools diagnostics on it, or another HDD tool, it's hard to tell past the fact I'm betting you have damaged the actual drive itself.
I tell many customers, a hard drive is like a record player (if you remember those things), and trying to run with it, or drop it while its running is not conducive to its health. Double so for the hard drive as it has 'heads' which you risk bashing against the 'disks' or 'records' which hold your precious data.
I can only assume you've fubared the internals somehow when it was dropped.
Note: if the old drive spins, you have a chance at repair/recovery of data at a reasonable cost, if it is NOT spinning, you could be looking at over $300-600 for a 'clean room' recovery.