How do I change out the T-Con card of a Samsung 40" LCD television?

i dont see but i think you heave problem vith t-con board

The problem is the T-con.
There is a faulty chip and need to be replaced.
Price is about 30-50€

maybe it is the panel eeprom,if the panel inverter is good which should be treated with experts

Bad t-con board or bad LCD panel. T-con board at Encompas Parts about $50.

U can't buy the T-CON board in any stores in anywhere in the world because this T-CON board it is not buy able it new u only can buy it as a salvage tv PCB board only.This T-CON board u can buy it as refurbish board only.Tries websites like Shopjimmy.com,Ebay.com to buy a refurbish T-CON board for the replacement.

It can be T-CON board or worst case the LCD panel itself. You can try reseating the ribbon cables between the T-CON board and the LCD panel first to see if it fix the problem.
If you are going to DIY and have proper tools, electronics knowledge, and know safety precaution then please read on:

Please see my basic troubleshooting guide here:
http://www.fixya.com/support/r5093881-lcd_flat_panel_tv_troubleshooting_guide
http://www.fixya.com/support/r6150077-basic_lcd_monitors_troubleshooting
Failed TV and Monitors: http://s807.photobucket.com/albums/yy352/budm
Learn about bad caps: http://en.wikipedia.org/wiki/Capacitor_plague
Capacitors kit: http://lcdalternatives.auctivacommerce.com/Default.aspx he can make you a set of caps.

Parts: www.shopjimmy.com

Please post back what you find.

Two causes: The T-Con bd is bad or the Main bd is bad.
Start with the T-Con bd first.

if sound ok and back light ok the t-con board or the panel itself is faulty.

try cleaning t-con board to lcd panel cable..........
if sam problem just replaced lcd panel

1.T-con board or related cables problem -- 60%
2.replace Main Board -- 40%