Wow, I really wish I could just magically fix it for you, and I can feel your frustration from here!
From what I can tell, it seems like you're doing everything right, although pictures is always helpful to verify these things.
First of all: I don't think you've damaged anything. The way USB works, it's not possible to receive data without also being able to transmit data, so if it works one way but not the other, that almost have to be a software issue of some sort. Did you try switching "newline" to something else and then back?
Next step: Try hooking up the the arduino uno again and make sure the strip works. Then have it go through the level shifter to make sure you have that part figured out.
Oh, and before I forget: you did cut the vusb-vin bridge on the teensy, right?
Sorry I vented my frustrations a little in my last post. I've spent quite a bit of time debugging this since then. All I'm trying to do now is return the saber to it's previous condition... working but having the LED flicker issue. I've replaced and re-soldered all the wires I messed with when trying the level shifter. This include the +5V and GND wires from the LiPower Booster to the Prop Shield +5V and GND. It also included the signal wire from Teensy pin 20 to the blade connector pin 3 (which connects to the LED strip DataIn). At this point the saber turns on, plays all the sounds and responds to all the button presses but does not light the LED blade at all. Also, the Serial Monitor is now working but I can't explain why I couldn't get it to work yesterday. Here's what is displayed when I boot the Teensy...
ID: 1 volts 0.00 resistance= 32.26
blade= 0
WS2811 Blade with 144 leds
Scanning sound font: done
Activating monophonic font.
unit = 0 vol = 0.50, Playing boot.wav
channels: 1 rate: 22050 bits: 16
Welcome to TeensySaber, type 'help' for more info.
I2C pullups found, initializing...
Gyro setup ... Done
Accel setup ... Done
Battery voltage: 4.25
Battery voltage: 4.25
I went on to re-soldered my connections from Teensy pins 21, 22 & 23 to the Gate pins of the 3 N-Channel MOSFETs because I didn't like how one of the wires felt/looked after all the moving around and bending. From here I've taken some voltage readings in an attempt to find my issue. Here's my results...
1) Voltage between GND on the Teensy and pins 21, 22 and 23 read 3.3V when the blabe is turned on (hum sound plays and Serial Monitor shows the blade being turned on). These pins drop to 0V when the blade is turned off.
2) Following this up to the MOSFETs the Gate on each of the MOSFETs reads 3.3v when the blade is on and 0V when off.
3) The Source and Drain pins on each MOSFET read 4.19V (source LiPo battery voltage which reads 4.21V when read directly and not attached to the saber) when the blade is turned on and the Teensy raises 3.3V on the Gate pins. Also, please note that the TeensySaber sketch is returning 4.25V which is very close and would indicate that the connection to +5V through the pullup resistor is good.
4) Following this up to the blade connector the voltage readings between the pin 7 & 8 (+ from battery) and any of the three lines from the MOSFETs (pins 4,5 & 6 on the connector) read 4.19V when the blade is turned on and 0V when off.
Based on these results I know the MOSFET part of the circuit is working and the Teensy is turning on and off power to the blade.
At this point I retested the LED blade through my Arduino UNO test rig and everything works (btw... the test rig has just three connections, the Arduino 3.3V pin connects to the center pin [8] of the aviation connector, the Arduino GND pin connects to pin 4 and Arduino pin 6 connects to pin 3 on the aviation connector). The test project simply uses the Adafruit_NeoPixel library to light and turn off each LED all the way up the blade changing the colors through some of the basic colors repeatedly. This lets me see that every LED on both strips are working properly plus it verifies at least pin 3, 4 and 8 on my blade connector. I really doubt anything happened to the assembled blade and any of the connections there.
At this point I would guess something is wrong with the data signal coming from the Teensy to tell the blades to light. Do you have any further ideas? Any other multimeter readings I can do to test the circuit further?
Thanks again for your help and support. Also... to answer your question... Yes, I cut the VUSB-VIN bridge on the Teensy.
Here are some photos of my electronics as they stand now. Please not that all the exposed connections were originally covered in shrink tube or electrical tape before all this debugging.