You may be also not receiving any output because kindle halted. When it finish loading/give some error it halts - no more info is sent through serial.
Try holding power button for about 15 sec - there should be info about power button pressed (after about 10 sec of holding it). Than after releasing power button it shoudl start loading from beginning.
One more thing - I didn't solder anything and was able to communicate with my Kindle. Just pressed ends of TTL cable with my finger through special tape (so there is no short circut) to rightr exits on mainboard. It's not very comfortable but for a brief moment it works
