I replaced main board on Mitsubishi LT-52244. Picture looks great, but I have no sound. Help.

That is an older model set that still has the backlight inverters. It may be one of those and it may be the power unit. Mitsubishi LT 52244 TV Parts

Hi,
Nothing on all inputs would suggest the Main AV board not processing signals, if all other functions such as volume, menu access, on and off operate normally the power supply board is probably functioning OK. Have a look at shop jimmy for an idea on price and availability for Mitsubishi LT-46144 Boards and spare parts:

TV Parts Universal TV Stands DLP Chips ShopJimmy

Hello. Before you start replacing parts, make sure your connections are correct. It sounds like you have connected a composite source to a component input. Composite is three RCA plugs, a yellow for all of the video, and a red and white for audio left and right channels. Component is five RCA cables, green, red and blue for video, and red and white for audio. if composite is connected to a component input, the picture will be black and white with squiggly lines all through it.

Try unplugging for 1 minute, then plug back in again. It appears that the unit is initializing, if it continues in that mode you may need the DM PCB

part# 921C549008

see the following website:

http://www.shopjimmy.com/catalogsearch/result/?q=921C549008

First check all input cables, make sure all cables are good & plugged in fully. then check with a DVD player to all HDMI & component inputs. if none of this solves issue you may need MAIN PCB.
PT# 934C335007 $139.99
http://www.tvpartsguy.com/servlet/Categories

Mitsubishi LT46164 has a known issue developing on the main board that causes what you describe (and other things):

http://www.coppelltvrepair.com/p/1635/repair-service-for-mitsubishi-main-board-934c374002-causing-dead-tv-blinking-loop-no-hdmi-no-audio-etc-problems

Tries tv unplug,replug it back about an hour later for the tv for a resetting back to the factory setting.Go into the tv menu go to Audio Setting go down to do a resetting back to factory setting.These steps will help the tv to get the tv audio back.

The most likely the TV has a power supply related problem. The most common thing to go out is the circuit board that supply power to the screen. Commonly called a Backlight Inverter Board.
I can't say it's 100% the problem because I can't actually look at the tv over the internet.
If the TV is still under warranty, go that route.
If not under warranty and If you have some electronic experience, you can purchase a Service Manual over the internet and diagnose the source of the problem and fix it by soldering in the new part. The Service Manual will give you circuit diagrams, test points, and part# lists. Usually, cost under $20.

I hope I shed some light on the subject for you.

replace the signal board (one with all the rca's on it) and not the main board if a plain antenna works OK