Need some advice about a couple A500's

[Argus]

TJ is right, try cleaning the disk drive internals with Qtips and isopropyl alcohol (rubbing alcohol).  The heads are probably dirty and give that characteristic grinding sound when so impaired.  There are stronger head cleaning solvents about but isopropyl usually does the trick.  I don't recommend a disk drive cleaning kit, as the pads on these can be too abrasive and the Amiga drive doesn't spin unless you prompt it to do so like on other computers.

Regarding the damaged A500, I've yet to see an A500 that was killed in transport.  These are rugged little buggers, and cosmetic damage does not end their lives.  More than likely something inside comes loose during transport.  Smartly Commodore (unlike the Atari ST), put most of the big chips inside the A500 in sockets so a quick push can reseat them or you can extract a bad chip and replace without soldering.  Try that on an ST!  Just take standard antistatic precautions (e.g. touch some grounded metal before you touch a chip).

[Argus]

The easiest way to get 1MB chipram on a Rev. 6 is to put a 1/2 meg expansion card in the trapdoor slot of the A500 and then modify a couple jumpers to access the extra 512K as chipram rather than the default slow/fast ram.  You'll need to have an 8372A 'Fat Agnus' chip though as well.  Most(all?) Rev. 6 m/b's should have shipped with an 8372A Agnus, though they're cheap to come by on ebay nowadays.

A similar mod can be done on a Rev. 5, though this revision is missing the jumper near the trapdoor slot, so it involves cutting a trace.  Rev. 5's afaik almost all shipped with the 'Thin Agnus' 8370 chip (NTSC), so unless the previous owner updated to 8372A, you'll definitely need the chip for the Rev. 5 board.  Open it up and take a look.

There's even a way to supposedly modify a Rev 3. A500, which is a very rare and buggy m/b version.  I used to have one but could never get it to work with 1MB chipram.

Instructions for these simple modifications are on the net.