LED TV Boot loop - UE40F6500SB

[TrisHCl]

Hi,

First post...

I have this TV, which was working, then suddenly would not turn on. It would get the clicking relay then flash up the screen for less than a second, off for a second then on again. Removing the plug the relay continues to click on and off for a few cycles, which I don't think it did before.

Left it a few months, then finally got round to taking the back off, and it worked as it should. So I tested various bits and all was well. Then turned it on again, and back to the clicking relay.

I disconnected the main board from the power board, and no difference. The relay clicks and the backlight flashes briefly. This then cycles.
I disconnected the backlights from the power board and no difference, still relay clicks.

The power board is BN 44-00622B - and has been mentioned on this forum before. Using this schematic https://elektrotanya.com/samsung_bn4.../download.html

I have 480V max 462V min on main smoothing capacitor pair, so I assume PFC is working.
I have 5.3V on the standby, which seems stable.

I went through all the electrolytics with a Peak ESR meter, and all seem ok. A few were 'leaky' in circuit, but ok out of circuit.

I reflowed all the hot components and transformer pins as this had been mentioned in various posts.

I'm not sure how this board should behave on the bench with the backlights disconnected. Would the relay click on and off with no backlights connected as it thinks these are defective ? If so, can I ground a pin to fool it ?

If the backlights are faulty, I'm not sure how to test as they all seem to work getting the brief flash, and there was the single episode where it started working again. I don't have a backlight tester, but they are not always reliable I had heard as they don't necessarily drive the LEDs hard enough - could get one from ebay if necessary though.

Does the relay continually clicking after the power goes off help with the localising the fault ?

I can send the power board off for repair for £50, but that would not help if there is a backlight issue.

Watched a lot of youtube videos including Michael Dranfield's, so I'm getting a better understanding, but hitting the buffers with actually fixing the TV !

Any help would be welcome....

Cheers,

Simon

[nomoresonys]

Can you post a good clear picture of the whole back.

[nomoresonys]

Test this loon, make sure nothing is burnt, test each wire for continuity. I use bread ties to stick in the ends so as not to deform the connector ends: https://www.ebay.co.uk/itm/196880084....c101800.m5481

[TrisHCl]

Are these pictures ok ?

[TrisHCl]

Tested Loon, and continuity between all wires at each end

[TrisHCl]

What is the normal behaviour with the mainboard and backlights disconnected ? Should the relay still cycle clicking on and off (on for a fraction of a second, then off) ?

Thanks for the suggestions by the way.

[nomoresonys]

Seems like a bad solder joint on a transformer, maybe go over them again to make sure, looks like there's 3 transformers on that board. Sometimes you can get a big glob of solder on it but the joint is not good. Can do a search for images of bad joints if needed.

[nomoresonys]

Something to try, unplug the wifi module cable at mainboard and try the tv.

[TrisHCl]

I've checked for continuity on all the transformers and reflowed the joints, and all were fine. I don't have the mainboard connected, so the backlights should come on and stay on if there is not a problem with the power board or backlights.

[nomoresonys]

Here's something i have encountered before, did a recap but had a bad solder on one of them and was getting the clicking. There's a way of testing the caps in circuit with a multimeter set at 20,000 ohms, by putting a probe on each leg, the meter should gradually go up, reverse probes and should gradually go down, may need to try a few times to verify, if that checks out maybe carefully take it down to backlight and check each with multimeter. Being a 40 it shouldn't be too hard if you take your time and go slow. Can check some youtube videos on backlight replacement for procedure tips.

[nomoresonys]

Of course this tv being circa 2013, I probably would have just recapped all the electrolytics just to eliminate them from suspicion.

[nomoresonys]

That single flash of the backlights can be a symptom of bad backlights maybe one or more burnt out, 11 or 12 years is a pretty good run for backlights, specially if they have been set at 100 percent for the whole time.

[nomoresonys]

Any update or did you give up and toss it?

[TrisHCl]

I retested the capacitors by measuring the resistance as above. All were ok. Phoned up a retired TV engineer who used to work near me, and he said he had zero success fixing that sort of fault. Currently it is in the boot of the car, as I had to clear the dining room table for guests at the weekend. I will get it out as the time it did work it had been in a cold room for a couple of months. Still would like to work out if the backlights are sending an error back to the power board or if it is the power board. There was a russian article on this TV on this forum somewhere I will search for.

[TrisHCl]

Hi, not given up on this.

i have found the tv sometimes starts up when I reconnect the main board. I have to poke and push at points on the power board, and eventually the tv turns on. The points are never the same, which is annoying. It tends to be on the cold side, but I can see the board flexing, so it may be something distant. It will stay on, even if I keep pressing components on the power board. If I turn the tv off then on, the tv goes into clicking relay cycles again. If I press the remote to turn off/standby then the TV goes back into clicking relay cycles again.

i am thinking it must be a dry joint, but once the TV starts up it stays on until it is turned off. Does that help localise the problem, I.e. once on it is stable even although the cause of the fault is still there. I'm not sure if it is just coincidence, but it seems more likely to turn on with pressing the power board in the morning, when the house is cooler.

Does this in anyway help to localise the fault. The backlights all work, and so does everything else when the TV gets past the initial startup hurdle. I am hoping this means there is nothing terminal wrong…..

any ideas gratefully received.

cheers,

[nomoresonys]

That poking/pushing to get it turned on makes me think it has to be a bad solder joint, most likely on a transformer. I would redo them all and touch up the rest too, just be careful not to bridge any joints. The joint doesn't have to look obviously cracked to be bad.

[TrisHCl]

Thanks, I will resolder all the joints on the cold side when I get back from holiday, and let you know how it goes !