Samsung LN40C540 Turns on when it wants to...

[ClaudioD]

Thanks in advance for taking the time to read and possibly help me with this issue. I tried searching for this issue but none specifically matched. Also, I would like to apologize in advance if some of my terminology is incorrect.

I have a 40" Samsung Series 5 LCD TV. It was purchased approx. 2 years ago.

The issue first began with when the TV was powered up it the standby light would flash 5 times and nothing would turn on. No sound, No backlight, and the standby light would remain off.

I would unplug the TV wait 10-20 minutes, plug back in and power up the TV. It would then turn on. The issue got progressively worse. I automatically related this to a cap issue as when unplugging it the caps would discharge.

Now at my job I have 2 technicians on hand which have helped me out. They have all the possible tools need.

The main power board was tested and all was believed to be fine. Capacitors were all individually tested all tolerances are proper. They also tested the rated of discharge which was fine. I did however replace the all of capacitors because had them in stock here.

We have gone over all three boards looking for cold solder points, we have tested and verified all voltages on the pinouts of all the boards. The issue is that we cannot pin point the issue. I could try turning it on right now and it will work, then turn it off again. I can go back in 5 minutes and turn it back on and it will just blink the red standby light 5 times and not power up.

When it does turn on it will function properly, It does not shut off randomly as some posts would claim with bad capacitors.

I also do not hear any relays click when it works, which leads me to believe the routing of power is not relay controlled but rather IC controlled.

I have the ability to test and confirm anything you guys wish me to test. Please if anybody can help or point me in the right direction it would greatly help.

Thanks,
Claudio

[Th3_uN1Qu3]

Re: Samsung LN40C540 Turns on when it wants to...

Had a 32" with the same issue, turned on after 20-30 minutes. Needs a new sub board, it's the board between the main board and the Tcon. You can confirm this by heating the board with a hair drier and power cycling the TV - it should start up right away. I have checked everything on that board and could not find the culprit - no bad caps, all voltages in spec, reflowed BGAs only to have it behave exactly the same. I believe it's either a bad trace on the board or an internal bonding defect in one of the chips.

Client didn't want to pay $45 for the board + $30 for my time, he took it back as it was and continues to put up with the issue... I'll be buying it off him when it craps out for good. I'm 90% sure replacing that board will fix it.

[ClaudioD]

Re: Samsung LN40C540 Turns on when it wants to...

Well wouldn't that theory contradict what the issue is. If heat (a blow dryer) would cause it to kick back on. My issue would be i would have to let it sit for 20-30 minutes before turning it back on. that means it would cool down in order for it to work properly.

[tom66]

Re: Samsung LN40C540 Turns on when it wants to...

Some thermal issues can work both ways. Expansion could cause something to work, so could contraction.

[ClaudioD]

Re: Samsung LN40C540 Turns on when it wants to...

The problem is that there really is no consistency with the issue. sometimes it requires 2 minutes to turn back on and sometimes it requires 20 minutes before i can power it back up.

Now not sure if this test helps but...

If I turn the power on, and the TV does nothing. If I unplug the input board from the power board the backlight turns on. This would lead me to believe that the input board is acting up and that its when when it is plugged in it does not let the screen come on. Again guys im sorry for my terminologies of the components. I am trying to keep it as layman as possible.

[Th3_uN1Qu3]

Re: Samsung LN40C540 Turns on when it wants to...

That's interesting with the input board, but could be just a coincidence. How does it behave if you unplug the Tcon?

Anyway, do try what i asked and heat up that board. You may be surprised of the result.

[tom66]

Re: Samsung LN40C540 Turns on when it wants to...

Many Samsungs will turn on the backlight with no input board due to pull ups on the back light enable pins.

[ClaudioD]

Re: Samsung LN40C540 Turns on when it wants to...

Ok so here are the results...

The i.f. board (the input board) was gently heated with a hair dryer to see if heat would allow it to turn on all the time and function properly. This did not work as mentioned by Th3_uN1Que, but it did however give me an idea to test the opposite extreme.

I took the I.F. (input) board off the case placed it in a zip-lock freezer bag (to eliminate moisture) and placed the board in the freezer for an hour. I took the board out of the freezer and hooked it up right away...

**SURPRISE, SURPRISE** I was able to turn it off and on 6 times in a row without a failure. The 6th time did take a approx. 10-15 seconds to boot up. I would assume this is because the board was now heating up.

So cooling down the input board temporarily fixed the problem.

Now I also want to not that there is no relay sound so I believe the "clicking" function is controlled by an IC.

[tom66]

Re: Samsung LN40C540 Turns on when it wants to...

The relay clicking is sometimes main board controlled, other times power supply controlled. If you have your meter, you can try checking if there's anything abnormal when it doesn't power up - care to post a picture?

[ClaudioD]

Re: Samsung LN40C540 Turns on when it wants to...

I have not physically located a relay. I believe an IC is controlling the same function. Either way, when something on the board heats up it cause the TV to not turn on properly.

[ClaudioD]

Re: Samsung LN40C540 Turns on when it wants to...

Tom66 what exactly would you like a picture of? I would be happy to take one.

[tom66]

Re: Samsung LN40C540 Turns on when it wants to...

I have encountered a voltage regulator before on a Samsung being faulty. Cooling it down made it work briefly. Same on another TV. If you can pick up a can of freeze spray (or compressed air - invert the can to get freeze spray) you can try selectively spraying areas until the set powers up.

[ClaudioD]

Re: Samsung LN40C540 Turns on when it wants to...

LOL...I just finished trying that exact thing. I came back to my PC and read your message of telling me to do so. I have seemed to narrow it down to an smaller area. let me have a look for the voltage regulators.

[Hobby 1]

Re: Samsung LN40C540 Turns on when it wants to...

Just saw this post and would like to add some info. I recently bought 2 of these sets for repairing from different people. Both about 2 years old and a couple of months different in manufacture dates. Both had been worked on by service techs who failed to fix them. The original owners gave up when presented with additional huge estimates for repair. One was told that he could not find the required part. One was completely dead, not even a standby light. The other would once in a while turn on but well after the 5 startup blinks. First thing to do was to replace all the low quality caps, even on the new power board that an earlier tech had sold the original owner. After playing with and interchanging boards between them, I determined that it was the input board that was at fault. On to ebay to look for parts. Almost no input boards available for the 40C540 model. After some investigation, I thought that the input board from the next model up should work (40C550). All it had different was a LAN connection. I ordered one to try it out. 10 days later, it arrived and I tried it. I put it in the set with the dead input board. It worked. TV powered up, tone and backlight during the 4th or 5th blink and it worked during several power off and on cycles. The other set, when it did power on, would power on long after the 5th blink.

Then I saw the post about cooling parts of the board. I put the half dead board in the refridgerator for 10 minutes and then installed it back into the set. It powered up on the 4th blink, just like the replacement board. I turned it off after a few minutes and tried again. It turned on well after the 5th blink. Powered off again and it would not turn on again.

Appears to be temp/contact related. I already ordered another input board for the higher up model but I would like to fix this half dead board. It appears that this is a common failure for this model. A sidenote here...the back panel has a punchout for the LAN connector. I just have to cut through the stick on label to use it. A bonus upgrade and repair at the same time. Now it will be an LN40C550 !

Has anyone narrowed down the area of failure?

[Hobby 1]

Re: Samsung LN40C540 Turns on when it wants to...

First picture is the main (input) board, the half dead one. The fully dead one is different and appears to be an earlier model. Second picture is a closeup of the part that when cooled by freezing spray allows the set to turn on. That part is under the small heatsink in the center. Cooling the bottom underside does the trick. I removed the heatsink and the 'leads' are under the very thin flatpak. No way to solder them again and I don't have a hot air pencil.

Anyone have any suggestions on how to re-heat the connections under this chip without destroying the board?

I closed up the first set with the dead board replaced by the LN40C550 main board. Correction on the upgrade. It has 2 additional connectors. The LAN port and a USB port.

I am waiting for the second board to fix the second set, but playing with the half dead board in the meantime.

[Th3_uN1Qu3]

Re: Samsung LN40C540 Turns on when it wants to...

Leads on the underside? That's either a QFN or a BGA. Reflow time... If you don't have a hot air gun, you should get one. Or if you really think you won't need it (you will), see if you could borrow one.

[tom66]

Re: Samsung LN40C540 Turns on when it wants to...

^Or a paint stripper. I've used one before in a pinch.

[Hobby 1]

Re: Samsung LN40C540 Turns on when it wants to...

Getting a hot air pencil is on my 'to do list'. I guess I can try a hot air gun and fashion some sort of funnel to direct the hot air under the chip. I'll practice with some scrap boards first, when I have time.

[mark_]

Re: Samsung LN40C540 Turns on when it wants to...

Hello

I know it an old (very old thread) but I hope someone is still following it.

i have a Samsung LN40C540F2F with the same problem. Did a reflow work? Just nailed mine with a can of air upside down and it started right up ... hit it in the corner where CN802 from the power supply connects.