Just got a new HDTV to replace the ancient-but-still-functioning tube TV since we canceled netflix and netflix/Wii was the only thing the old TV would get other than DVDs.  The new one has HDMI ports so we can use the Roku on it and watch other stuff.  

The new TV also has a digital tuner, unlike the old one, so I was also excited to watch regular TV for sports, news, etc. while I work out.  HDMI works for Roku, RCA works for old Xbox, and coax-in works for over the air channels if I do a little dance and hold the antenna just so.  But when i connected the cable to the TV and scan for channels, it finds nothing (in both Air and Cable scans).

Our cable is TWC boxless.  The drop from the pole goes into a regular splitter with one output going to our main TV and the other one going to (formerly, only) the modem.  

I tried splitting the coax at the modem end with a 3.5dB splitter: no channels.
I tried splitting the coax at the modem end with a 6dB tap (modem:tap / TV:out): no channels.
I tried splitting the coax at the modem end with a 6dB tap (modem:out / TV:tap): no channels.

In all of those configurations, the internet worked fine.  The modem reports about +/- 1.5dBmV (typically on the higher side around +1.5) with around 38dB SNR with the coax from the wall (coming from the main splitter at the drop) connected directly to it and it reports the expected dBmV decreases with the splitter and tap.  

I suppose the next logical troubleshooting step would be to try the new TV connected to the coax that currently feeds our main TV and/or the coax that feeds the modem and see if it works there but, since cable was sort of an after though, the new TV is already pretty well bolted down so I thought I would ask here if anyone can think of or immediately spot any issues with the setup.

When I looked at the TWC-installed splitter at the drop, it was dark so I didn't inspect it well, but it just said "splitter" so I assume that it has the same signal coming from both outputs.  If that is the case, and that signal runs the main TV, I would assume that signal coming from the output of my tap would be similar and run the new TV.

New TV has a shitty ass tuner, I really am sorry but new tvs dont have tuners worth a fuck as most people feed tv with hdmi

How long do you think that has been the case?  Granted, this new one is a really cheap one just to look at while I work out or if we have guests staying over, but our main TV is only a couple years old and neither TV has a problem grabbing over-the-air signals from a cheap indoor antenna and giving 1080p video from it.  It seems like if it could tune that, it could tune something from the cable co.

You have to get the small box adapter from Time Warner, this I know to be true.

I think you're right.  I forgot to post a follow-up, but I believe I've identified the issue.  Does TW charge for that box, or do you have to rent/buy it?  I think I found one online for around $30.

While this TV has an ATSC/NTSC digital tuner, what it needs to have for the TWC channels is a QAM tuner.  Although this wasn't a feature that I was looking for in the set, I think it turns out that the model that I received is slightly different than the model that was in the product photos on the order page, which does have a QAM tuner.  The model number in the description is truncated and could be either model - the missing last couple characters would differentiate them.

I guess my first try will be to see if I can get them to replace it with the pictured model that has the QAM tuner.
If not, I'll see if the tuner box from TW is free.
If not, I'll have to decide if my cheap ass wants to shell out for the tuner.  Although it would be nice to have the other channels wired into it, I can watch almost everything I'd be interested in during a workout via the antenna or Roku - even if the news comes from SkyNews and CNN .