Samsung LN40A450C1DXZA

[Caleb]

Re: Samsung LN40A450C1DXZA

well my ld is only 1 volt but that is on the power board, I thought it was probably another type of feedback signal coming off the inverter. Google didn't help me out with an exact explanation of what ld is and or does for the circuit. So Budm if you feel so inclined could you please explain.

I tried bypassing the transformer with the 6v feedback and I get a solid backlight for about a second followed by about 2 seconds of flickering with all harnesses plugged in, so I think the bottom bulb is done for as well as at least one more. I'm planning on tearing the rest of the way into this tomorrow morning and see what I can figure with the ccfls.

I went and looked at the Jensen and its a 42 so I don't see the bulbs fitting. Is there a good source for new ccfls, or do you guys just salvage the good ones from broken screen TVs? I may end up just replacing the ccfls with led strips, it worked well for another TV I couldn't get a new inverter for.

[johnboy1313]

Re: Samsung LN40A450C1DXZA

In two experiences with bad CCFL's, I used salvaged bulbs both times. One time, I called a guy on Craigslist that was advertising to buy broken TVs and bought three bulbs from him for $25. The other time, I needed several bulbs for a Samsung LN40B630NFXZA so I bought a 40" Sony with a broken screen for $10 and took 14 of the bulbs from it.

[Caleb]

Re: Samsung LN40A450C1DXZA

Alright I tore it down this morning, Couple thing to report, first I am still getting about a second of steady back light followed by two seconds of flickering before it shuts back off, I took a short video so I could pause the view when they are all on. All seem to be the same intensity except the second one up from the bottom which to my eye appears to be double the intensity. I bypassed the transformer for that one> didnt change anything. after soldering it back on I retested the ld and got 10.95vdc with all cords plugged in as well as 1.29vac on the fb test point. Really confused as to why I suddenly have good readings other than maybe a loose connection that I reconnected by accident. Sooo how do I determine which bulbs are bad or do you recommend to replace them all, or just eliminate them altogether and go with leds?
<iframe width="1280" height="720" src="//www.youtube.com/embed/fJDLQ73lzdo" frameborder="0" allowfullscreen></iframe>
Not sure if the Iframe will embed or not here is the link
http://youtu.be/fJDLQ73lzdo

[Caleb]

Re: Samsung LN40A450C1DXZA

Well Ive been trying to find some ccfls to try out, I tried removing the ld wires from the connector and also tied 150 ohm resistor from fb to ground, no changes still shuts off after a second. Is there any way to get it to stay on so I can try to find out which bulbs are causing my trouble?

[Caleb]

Re: Samsung LN40A450C1DXZA

Finally go some new ccfls today, is there any test other than randomly replacing them to see when it starts working? Anybody got a link to a homegrown ccfl tester?

[Caleb]

Re: Samsung LN40A450C1DXZA

Ok swapped out the ccfls 4 at a time until all had been replaced with no change. Still turns on flickers then shuts off. Soooo I guess we are back to power board/ inverter troubles. I found a couple links describing ways to bypass the shut off signal by grounding out the timing cap on the controller ic. But Im not sure what pin that is on my chip. Anybody have any idea which pin that would be on a chip marked A35AF 005? I couldnt even find a datasheet on google relating to this one. How possible is it that the feedback circuitry on the power board is messed up and causing this? Or should I concentrate on the balancer board

[william1021]

Re: Samsung LN40A450C1DXZA

Does the backlight flash at power up and then cut off?

I have the same TV. My backlight does power on and then cuts off when it is unplugged. Any help would be appreciated with what could be wrong with the set. When trying to power up the tv the screen is just black and the red light stays on.

[Caleb]

Re: Samsung LN40A450C1DXZA

So on yours the backlight stays on until you unplug it? That in my mind points to tcon or main board trouble. It would help me diagnose mine, if you measure the error points on the balancer board and post your results. I would check the fuse on your tcon first and make sure the board is getting power.