Samsung LN40B500P3F - Won't turn on

[budm]

Re: Samsung LN40B500P3F - Won't turn on

Good, the PS-ON is good, the switched 13Vs are good, the boosted Voltage is good.
I did not read all your posts, so what is the TV not doing? No backlights?

[Mr.E]

Re: Samsung LN40B500P3F - Won't turn on

Good, the PS-ON is good, the switched 13Vs are good, the boosted Voltage is good.
I did not read all your posts, so what is the TV not doing? No backlights?

The family member that I got it from said that the TV would randomly turn off. When I tested it, it would run fine for a week and then it shut itself off. The next time I tried starting it up a couple days later, it would turn on for 5 seconds, and then it would turn on. I was unable to get it to stay on after that.

Currently, it is on and appears to be fine.

[budm]

Re: Samsung LN40B500P3F - Won't turn on

You need to take the VDC ON CN802 when it works and when it does not work, you also need to see if the backlights still stay on but no image on the screen when it stops working, or the backlghts goes off.
The word turning off may not be the right word unless it acts as if some one turns off the power switch. Backlights are off does not mean the TV is off.

[Mr.E]

Re: Samsung LN40B500P3F - Won't turn on

You need to take the VDC ON CN802 when it works and when it does not work, you also need to see if the backlights still stay on but no image on the screen when it stops working, or the backlghts goes off.
The word turning off may not be the right word unless it acts as if some one turns off the power switch. Backlights are off does not mean the TV is off.

The tv ran fine for the past 3 days straight, and then when i got home from work today the screen was off. No backlight, and the CN802 is showing 390VDC.

The red light is illuminated on the front of the tv, but the tv will not turn back on. When i press the on button, absolutely nothing happens.

I haven't tried unplugging and plugging the tv back in yet.

Thanks

[budm]

Re: Samsung LN40B500P3F - Won't turn on

So when you turned on the TV when you got home, there is no backlights but you do have boosted Voltage of 390VDC on the main filter, that means the PS-ON signal is good, so now you need to find out if the bl-on (invr-on) is present or not.

[Mr.E]

Re: Samsung LN40B500P3F - Won't turn on

The TV is now turning on again. I tested invr-on when it wasn't turning on, and it was showing 4.7 VDC. It's also reading 4.7 now when I turn it on.

[budm]

Re: Samsung LN40B500P3F - Won't turn on

OK, the bl-on and the Voltage booster are OK but no backlights, so we now have to look into the inverter circuits of this bn44-00264, the lamps.

[Mr.E]

Re: Samsung LN40B500P3F - Won't turn on

I should clarify that the backlight is now turning on, in case that wasn't clear. Is testing the lamps still necessary?

[budm]

Re: Samsung LN40B500P3F - Won't turn on

"I tested invr-on when it wasn't turning on, and it was showing 4.7 VDC." and now the backlights come on again, so you either have inverter problem or lamps problem.
The key point is that if the bl-on and boosted Voltage are present but the backlights are not on then we can eliminate the main board problem or the boosted power supply.

[bondo123]

Re: Samsung LN40B500P3F - Won't turn on

hi I had the same problem as VEAUX on my SAMSUNG LN40B640R3F, uses BN44-00264A power board, the 3.15 AH fuse blew and TV was totally dead, thanks to this thread, determined the two QI820, QI821 FDPF7N50U MOSFET shorted, S-D tests 0.3 ohm, G-D is 40 ohm, took them out, put in new fuse, now on standby big caps tests 167V and when power up 370V; kill-a-watt shows 0 W on standby and 38W power up; tv powers up and down normal with the Samsung tune, digital out on main board has a red glow so power is getting to main board, clicking the remote the red LED light flashes, backlight is off since MOSFET are taken out

I should be seeing a dim "no signal message" or the menu when tapping "menu" on remote control, but I am not seeing anything....the screen is totally black when shined with a flashlight, is something else wrong ?

also I am trying to get the new MOSFET, digikey sells FDPF7N50U-G with logic level gate, and the standard FDPF7N50U is not available

http://www.digikey.com/product-searc...ords=FDPF7N50U

is the logic gate version an equivalent substitute ?

[1specman]

Re: Samsung LN40B500P3F - Won't turn on

is budm still active here. i need help with my samsung board

[dick_barton]

Re: Samsung LN40B500P3F - Won't turn on

Shopjimmy's replacement parts for this power supply are comprehensive and may be worth you taking a look at.

[vinceroger69]

Re: Samsung LN40B500P3F - Won't turn on

is budm still active here. i need help with my samsung board

budm is firstlly though is your tv the same one as in this thread? maybe tell us what the fault is with your tv also what you have done so far to test and post some good clear pictures of the boards used in the tv also one showing all of them so we can see how there connected. If your tv isnt the same model number as in this thread start your own new thread with the above information in it thanks.

[nartac]

Re: Samsung LN40B500P3F - Won't turn on

this is an old thread but I want to express my gratitude to veaux, budm, and all those who contributed to the resolution to the problem with this TV. I have the same TV and my problem also was like veaux and it was also repaired after replacing the mosfets. Without this thread and all the knowledgeable people on this forum, the TV would have been in the landfill and more money would have to be spent to purchase another TV. Again, thanks so much.

[neilc6]

Re: Samsung LN40B500P3F - Won't turn on

I had the same problem on this model TV. Removed the FETs and they were shorted on my ESR tester. Fuse was blown. Ordered the following parts on Digikey: 2 x FDPF7N50U_G-ND (QI820, QI821 MOSFETs) and F2376-ND (FM802S fuse) and TV is back up. No need to buy repair kits which have the same parts. The FETs are a bit tricky to pull out and have small grommets in the holes for source and drain. I did dent one of the filter caps unscrewing the FET from the heatsink so you need to be a bit careful and use a small philips screwdriver.

[nestor_nelida]

Re: Samsung LN40B500P3F - Won't turn on

Hello,

My problem it's with the FS801S fuse, not with the FM802S fuse (that it's fine).. Do you know what I need to change? Thanks.

[dick_barton]

Re: Samsung LN40B500P3F - Won't turn on

With the power off, check between the legs of QP801S & QP802S for short circuit.

[nestor_nelida]

Re: Samsung LN40B500P3F - Won't turn on

With the power off, check between the legs of QP801S & QP802S for short circuit.

thanks dick for the clue:

A photo of my board:
https://drive.google.com/file/d/0B93...pOZHh4QlU/view

I did the check. Between the leg, from up to down, 1 and 2 are continuity on both, there is not continuity with the 3 leg. Are you sure this is not normal?

[nestor_nelida]

Re: Samsung LN40B500P3F - Won't turn on

I just read the "Voltage Regulator (LDO) testing" thread. And for do that if I understand well I need to power ON. It's dangerous the voltage on that regulators or I have any voltage at all if the fuse is blow?