I just purchase the 19" TruTech w/DVD from Target just so Comcast could set up my cable. The installer said that this TV was not list in the code book so he did not set it up (and I paid for installation, what a rip - but that is beside the point). After trying a couple of codes for Apex Digital and Funai, I figured "Heck, Vizio is a new brand on the market." So I ran through the code for them. Lo and behold, it was the last code I entered - 11758 that works for everything. It may not solve your issue for a different model but it may get you in the ball park or get you to thinking on how to solve yours.
Press the TV button once. Press and hold the Setup button until the TV button flashes twice. Enter the nuneric code. Press Power (TV will turn off if works). Repeat 2 thru 4 until you vind the correct code that works for all functions (use the Comcast Remote Contol guide to the numbers).
