Samsung UN40D5550RF power cycling

[matt@bdtinc.com]

I have a Samsung UN40D5550RF that as soon as it is plugged in, it powers itself on for a few seconds then turns itself off for about 30 seconds then back on for a few seconds and continues this cycle.

I am pretty sure that the PSU is ok, when i remove the 14-pin cable from PSU to main board, the back light comes on and stays on and all voltages are correct. I removed the T-CON, speakers and power buttons from the main board but still get the same results, as soon as the PSU is hooked up to the main board, the cycling starts.

Aside from the fact that I cannot even find a replacement main board (Samsung part# BN94-04513B) , I would like to repair this rather than throw parts at it. I spoke with someone who repairs similar issues on Samsung main boards (just not MY model, he has no way of testing it!) and he said often times it is a voltage regulator on the main board. I read the sticky on this forum that explains how to test voltage regulators but since I don't have a steady power source when the board is connected, it has been very challenging. Does anyone have any pointers that can help me out? Is my only route to remove each SMD VR and will i even be able to test them out of circuit? Anyone fixed this problem in the past? Thanks in advance!

[budm]

Re: Samsung UN40D5550RF power cycling

http://www.shopjimmy.com/samsung-bn9...d5550rfxza.htm, not cheap and not in stock.

I doubt that it is V reg problem, try heating the board with hair dryer especially around the BGA chips to see what happen.

[Agent24]

Re: Samsung UN40D5550RF power cycling

Have you checked for shorts on the power inputs to the mainboard?

[graveboy81]

Re: Samsung UN40D5550RF power cycling

I have a similar issue but its with a Samsung ln52a650 series. It powers on just fine. And it only does the power cycle when something is playing like if the cable is hooked up or my Xbox etc. Im clueless as to what it is and need some help. I tried to post a new thread instead of piggybacking on this one but its a similar issue.

[matt@bdtinc.com]

Re: Samsung UN40D5550RF power cycling

Ah! I did not think to check the power inputs for shorts. I will do that tomorrow before I try to "reflow" the BGA chips. Thank you both for giving me direction! I will update with my results.

[Agent24]

Re: Samsung UN40D5550RF power cycling

Ah! I did not think to check the power inputs for shorts.

Something shorted or drawing too high current but not totally short could cause the PSU to power cycle, although it seems odd it would stay on for several seconds, and take so long to attempt a restart.

I think I missed an important detail before too. (sorry!) I re-read your post and where you said it comes on by itself, I get the idea now that it's the mainboard repeatedly sending the power up and then power off command to the PSU over and over.

You should identify the PSON line to the PSU and find out if that is going on and off as well.

Also, you could try disconnecting that line to the PSU, leaving everything else plugged in, and see what happens. PSU should come up in standby, not power cycle, and you should see PSON output from the mainboard going up and down instead, if the mainboard is faulty.

[matt@bdtinc.com]

Re: Samsung UN40D5550RF power cycling

After reading the above posts, that was the next thing on my mind.. so if the 14-pin cable causes the issue, i need to narrow down which pin (s) are actually causing it. Then , at least i know what part of the circuit to start tracing and minimize the testing of random SMD components. That is why I think it is invaluable to be able to bounce ideas off of experts. Sometimes you hit a wall and don't see what direction to take next. Often when I am stuck I ask a colleague to give a fresh perspective with no background info just to get another approach that I may not have thought of. Thanks again! I will get this solved and hopefully help others!

[matt@bdtinc.com]

Re: Samsung UN40D5550RF power cycling

I also just realized i can put my DMM in DC AMP mode and see how much each +rail draws and see if anything seems too high. You guys are awesome!

[budm]

Re: Samsung UN40D5550RF power cycling

"I am pretty sure that the PSU is ok, when i remove the 14-pin cable from PSU to main board, the back light comes on and stays on and all voltages are correct." The power supply and the inverter are fine.
So if the main baord is drawing too much current then you should see the standby Voltage going up and down.

[Nick's Tvs]

Re: Samsung UN40D5550RF power cycling

Its going to be an eeprom issue.
IC 1302
Got the same set with this issue. Its bad software on that nand chip. Unfortunately can't find a good board to copy the chip and fix the set.
If anyone has this board for sale, please let me know I will pay for a rental on the board so I can copy that chip and can send the board back so you can sell it a second time to someone else.

[victor_cj]

Re: Samsung UN40D5550RF power cycling

I had UE40D5500RW with SEMS21 IC1001 and K9GAG08U0E IC1302 faulty.

[Nick's Tvs]

Re: Samsung UN40D5550RF power cycling

Hey got that board fixed, if anyone else is having issues with it let me know.

[Southernyankee]

Re: Samsung UN40D5550RF power cycling

Yes same issue here. Power cycling ect.. how did you fix?

[budm]

Re: Samsung UN40D5550RF power cycling

Hey got that board fixed, if anyone else is having issues with it let me know.

How about letting us know exactly what you did to fix the problem?

[thebear13]

Re: Samsung UN40D5550RF power cycling

Hey got that board fixed, if anyone else is having issues with it let me know.

Hey, how are you doing, could you help us out telling us how to fix this problem, thanks!!!!!

[fcisolutions]

Re: Samsung UN40D5550RF power cycling

Matt, did you ever fix this TV? Just curious if re-flowing the board worked. Thanks.

[bluestone]

Re: Samsung UN40D5550RF power cycling

I have this same issue with samsung ue40d5520rk, I need help to fix it

[Nick's Tvs]

Re: Samsung UN40D5550RF power cycling

You have to replace the Nand chip IC1302. The problem is getting the software off the chip since the chip itself is damaged. I was able to get a hold of a good chip and downloaded the software from it and onto a new one.

http://www.nickstvs.com/store/p1595/UN40D5550RF

[jellytot]

Re: Samsung UN40D5550RF power cycling

Hi Nick. Any chance of a copy of the nand dump..?

[MICROTECHSERVICE]

Re: Samsung UN40D5550RF power cycling

hi you can do a temp repair using freezer spray, spray it on the nand chip. and switch tv on, get the latest firmware and flash the nand chip, 90% of the time cures the problem then copy the nand contents over.