by beyondbuxton » Mon Nov 26, 2012 8:51 pm 
			
			After finally (it took 34 days) receiving my ebay-purchased PL2303 USB TTL (3.3v) serial adapter (paid $2.31 for it), I managed to "unbrick" my PP4.  Which, for me, wasn't as bad as I had feared as I had made backup copies of all the files I modified.  After hooking up to the serial console, I mv'ed the backups into place, rebooted and successfully followed the awesome archlinux install information.  Et voila, a booting box!  (thanks again moonman)
For those reading this and scratching their heads because they've never used a console connection, it's really pretty easy.  There're directions for using a USB TTL scattered around various places.  My hope in coming back to do this update is that somebody else who finds themself where I was will have this as a reasonably complete guide:
After receiving the (tiny) PL2303 USB TTL adapter, I had a few things to do before hooking it to the PP4.  In my case, the OS on the rescue machine is Fedora linux (I can't really speak for other OSes, sorry).  I needed to install libftdi and minicom.  Configuring minicom wasn't difficult at all.  The only thing I had to do to the minicom config was point it to /dev/ttyUSB0.
Now, for getting it connected to the board.  I did not have a fancy header/connector for the pins attaching to the PP4.  I accepted a little risk here and carefully connected the wires directly to the amazingly small holes that form the serial interface on the PP4 board.  The GND pin was the one closest to the SD card slot then TX then RX.  I did not connect anything other than those 3 pins.  You will want to be very careful that these pins do not cross each other.  NOTE: the TX&RX pins will need to be swapped.  So.  In my case, on the PP4 board, I had black wire for GND, yellow for TX and red for RX.  On the other end of the cable (where it attaches to the USB TTL adapter), I had black for GND, red for TX and yellow for RX.  (the RX&TX need to "cross over" so that RX on the PP4 end of the cable is attached to TX on the USB TTL end)  I hope this isn't confusing - please ask if it is.  If you do hook it up incorrectly it will not damage anything, it just will not work.
Lastly, the serial console session: if you've ever seen a linux box boot without the splashscreen (with a crazy amount of text scrolling by on the screen), that is what this will look like when you have your PP4 attached and supply power to the PP4.  There's no magic here.  When it's done booting, you will be dropped directly to a command prompt, no login required.  It is at this point that you can (hopefully) undo whatever damage was done.
(as an aside, if you do not get all of the way to the command prompt, instead getting a kernel panic, ensure the the filesystem you are booting from is ext3 - I learned this the hard way)
I'm happy to answer questions/explain what I wrote above.  If you need more advanced information than this, please ask the larger audience as I am by no means a guru.
Thanks and good luck!
BB