Where do you get and how much is a power supply board?

SOURCE: red light on power button flashes, but no picture....blank screen

I would suspect a problem in either the backlight assembly, or the power supply that drives it. If it's the power supply, the part may be over $100.

SOURCE: Samsung LTN1765 has blinking green power indicator, but no picture or sound

Try replacing C51, a 10 microfarad 16v. surface mount electrolytic. It's near IC23 on the upper center of the board.
This part had high ESR on a couple of sets I serviced which
kept the power supply from starting.

SOURCE: no picture but has sound

your bulb has burnt out

SOURCE: Samsung TV won't turn on- trying to fix it. A challenging problem

I had the same problem. I live in NJ and called the local authorized "service provide" listed on the Samsung website. What a joke. Quoted $350 just to show up, never showed up. So I opened my own TV. Took off the plastic back (10 screws) took off the large metal RF shield (12-14 screws) and noticed a blown component. The markings on the component were KL15L and it is apparently an NTC Thermistor. Obviously it got fried and not knowing if there was other damage I decided to set out to replace the entire Power PCB Board Assembly and not the component. There were two part numbers on the assembled board (BN97-00457E & BN94-00622E). After searching online I also found a suitable replacement number for these (BN96-04896A). I found two places who claimed to have the part or have it on order (shopjimmy.com and vancebaldwin.com). After placing orders with both and having neither come through, I broadened my search and found out that the LNR409D was basically the same model as my LNR408D so I looked for its Power PCB Board Assembly part number which turned out to be BN41-00521B. Google search for that part number showed the item available on ebay. I bought it a week ago (ebay 260311519904) for $144 plus $12 shipping. I removed the bad board an hour ago (6 screws about 7 connectors) installed the new one, plugged in the connectors, replaced the covers, plugged in the TV... AND IT WORKS!
Suggestion: If your TV is out of warranty then open it up (what have you got to lose) and see if the problem is obvious and maybe something you can fix (replace) yourself. The parts, spare boards, etc. are out there if you look.

SOURCE: samsung lcd tv ltm1755b won't turn on (power light stays red)

Problem: Samsung LTM1755B with only a blinking yellow LED when you try to turn it on.

Solution: I just had one of these come in. I opened it up, and found the U501 capacitor a little suspicious looking, in that it had a deformed top. It was a 470uF 16V electrolytic 105degC 10mm x 12mm. I replaced it with a very good quality 1000uF 16V electrolytic 105degC 10mm x 16mm Nichicon UHN1C102MPD. After that repair, when I tried to turn it on, the LED was yellow for a second, then green, then I got a picture, and it appeared to work great. I then asked the owner a week later how it was working, and they said it was working just like new!