does my tv really have a cablecard built in and if so how do i find the serial number

Hello,
I have mitsubishi LCD Flat Panel HDTV LT-40148
It has a digital tuner. I just lost a bunch of comcast channels due to going to "new digital frequencies". I scanned for more channels but no new ones appeared. I do however get a bunch of digital channels from comcast already as it has a built-in digital tuner. Last night 20 channels disapeared. Comcast says i either need to get cable card or give them the serial number to my cable card so they can activate it. Mitsubishi support today told me I have a built in cablecard which is why i dont see a slot for one. Can anyone verify this? If i do have a built in cable card how do i find the serial number for comcast to activate it?

I wonder if they have a removeable cable card, like the smart card that the Dish Network uses or if it is just some sort of peripheral device like a modem in a computer?

You should be able to go into systems information and the device card number should come up - but I don't know why the manufacturer didn't tell you how to do that when they were on the phone with you.

It appears the 46" model has the built in card (see: http://www.youreviewelectronics.com/reviews/lcd-tv-reviews/mitsubishi-lt-46149-review/ ) but not the 40 " model (see: http://www.youreviewelectronics.com/reviews/lcd-tv-reviews/mitsubishi-lt-40148-review/ )

Uh... it has a built-in CableCARD-ready tuner. The tuner is built-in. The card must be obtained from/installed by the service provider.

Do you have a link? The ones I listed show that the 46" model has a built in cable card tuner but not the 40" model.

Right from the link above for the 46"...
Bold by me

The requirement for a cable box is completely done away with by the built-in CableCARD-ready tuner. Inserting a cable card is sufficient to watch all channels which means you can have one less box cluttering up your room.

The OP was asking about a cable card tuner and a built in cable card. The 40" has neither so I did provide an answer to his question.... At least IMO...

Effectively, yes. You said the 40" wouldn't do what the OP thought it would do. That's surely true. (It's just that the 46" wouldn't either, at least not without the service provider providing something extra.)