Yet another Samsung QLED Boot Loop

[Takeatry]

Samsung QLED QN50Q — purchased 2022 started experiencing a delay in the picture coming on in the morning less than 2 years later. Did not know the term boot loop at that time. As the loop delay ran into a few minutes did all the recommended troubleshooting, soft and hard reset, changing cables and outlet locations, no help. As the delay increased contacted Samsung tech group and allow them remote access the tv. Tech was moving too fast to see exactly what he was doing but this ultimately it was also no help. Lived with the delay until it stretched out over 6 hours. Pulled of off the back cover checked voltage on the PS. Steady 13v. Removed cable from PS to main Board, back lights came on stayed on. Removed ribbon cable from MB to panel, back lights came on stayed on. Removed ribbon from right side of panel, no picture but no loop. Removed left side same result. Saw some post with clock signal issues so tested that area. VGH was 25v VSs 5v. Did not document all the other test point at that time just confirmed there was some signal on each. Although I know I read it on number of post I wasted some diagnostic time as I did not put the jumper wire on the MB. Once I did , i could see the issue was on the right panel as it stayed dark when I removed the ribbon between panels. 3 times in different ares with different widths of tape I got a perfect picture. Problem was each time as the tv sat unused overnight or for a few hours, when I turned in on it when back into the loop. Started looking at mostly the capacitors on the right panel. I am not an expert and I am using a low end analog multimeter so I was never quite sure what I was reading. I did notice in resistance mode I would read no resistance in one direction and some in the other. Guessing this was normal. I did get some strange reading at a capacitor marked C02. No movement of the meter dial in either direction. On occasions when the tv was working I also took some voltage reading at as many capacitors as I felt safe to put the probe on. Again some voltage reading in one direct and little or none in the other. Except for C02. This had a reading of 7v on both sides. As I was going through this whole process I was always curious why the tv came on sooner or later. The only thing I could think of is at some time the unit got warn enough to cause some expansion and eliminate the loop. I did use a blow dryer on the right panel some days ago and the loop time was greatly reduced. Following this thinking after I saw these readings at C02 I put the blow dryer directly on this area. Once this morning it started within a couple minutes. I let the tv sit for 6 hours. When I turned on the loop began. I turned off and started blow dryer for a few minutes. Turn on again and it started immediately.
i am hoping I may have found at least part of my problem. Looking for experts to see if my thinking is sound. If so where would I find information on which capacitor to change out. I have seen online that it is a delicate process.

[CapLeaker]

With the TV on, go to the bad suspected capacitor, turn your DMM to AC voltage and see what you get when you measure across its legs. As capacity goes down and the ESR gets higher (you lower the ESR by heating up the bad capacitor) you can measure AC voltage on it. Of course a good cap should have next to none AC on it… so I wonder what you get. I guess this is the next best trick since you don’t have an ESR meter. You also can solder a good capacitor in parallel with the old one and re test.

[Takeatry]

Now a new wrinkle. 2 days in row since i sent the post the TV picture came in as soon as I turned it on. Yesterday I just turned it off. Today I tested for AC voltage. Checked my meter for normal household line voltage and it was accurate. Tested across the cap and measured nothing. Dropped the scale down to 10vac. Still nothing, but as I was positioning the probe I noticed the dial move to <1v with only 1 lead touching the cap. Read this small voltage on both side of the cap with only the positive lead. Then even with the ground lead touching got the same result. I thought I would leave the tv on to see if any reading would change as it warmed up. New issue- all the times the tv started it stayed on for hours. Today it shutdown. Thought I might have turned it off accidentally. So turned back on and less than a half hour it was of again. Not in the loop but off.

[CapLeaker]

You measured nothing on the cap, because your DMM isn't either auto ranging, or you had it on the wrong scale. You can do the same thing with an oscilloscope, as it makes it visual. Yes, the AC would be below 10V scale. You didn't see anything AC, there isn't any problem this cap.

To your new issue… got no idea why it turns off now. Is it off (as in stby), or is just the picture black?

[Takeatry]

Picture goes into stand by. To be clear on measuring the cap. Leads should be on either side of the cap while tv running?

[CapLeaker]

Yes. Just be careful no to short anything, otherwise you’ll be in some deep sh*t

[Takeatry]

Not using digital multi meter. Only low analog

[CapLeaker]

I have a hard time imagine that the cap is dead already. I mean the possibility is there, but they should last longer than that, since the TV is not very old.

[CapLeaker]

Is the auto shut off feature enabled maybe? Do a factory reset and see if that helps.

[Takeatry]

Before I try that. To check the function of my analog meter, can I find another cap the is big enough not risk shorting something out and put the leads on both side of it to see what reading I get. Assuming still on the 10 v range

[CapLeaker]

You would need to have a bad capacitor first place.
read this: https://www.badcaps.net/forum/troubl...repair?t=71608

And this: https://www.badcaps.net/forum/troubl...-hall-of-shame

[CapLeaker]

Oh! Before I forget it. Depending on how you measure this, specifically with a device like an oscilloscope that is connected to power mains and measuring around on the primary side… could go BANG! if DUT isn’t isolated with an isolation transformer. Measuring isn’t always as easy as it sounds, with certain pieces of equipment.

[Takeatry]

I Read the links, beyond my knowledge level to fully understand. Also I do not have an o-scope. Auto shutdown was set at 4 hours. Did a factory reset and the tv worked fine for 3 hours before I turned it off. As much as I would be ok with it, I can't imagine factory reset is my overall problem as I have done at least 2 other times and Samsungs tech group also did it. I will try to start it again tomorrow and over the next few days and see what happens. I think I may have put the wrong info in my opening post. When I check C02 for resistance my dial goes to zero in both directions. I know testing components in a circuit is not always accurate. Maybe I'll look at upgrading meter to DMM. Thanks for your help.

[CapLeaker]

You should see high resistance on the cap. If it's zero there is a short. But if there is a short, the TV wouldn't work at all. Maybe there is something wrong with your analog meter?

[Takeatry]

As expected when I turned the TV on the next morning it stared the loop. I am in the process of ordering a new DMM. I did pull my analog meter apart and cleaned all the contacts. I was able to measure high resistance across C02 7000 ohm. Checked it on the x10 setting and x1K and the values were the same. Also used the AC setting to check my thermostat, which read correctly at 24vac. Found no AC across the cap with tv running. I don’t have the expertise or equipment do do a proper analysis of a TV, but I try to use common sense to see where it leads me. I put the common lead on the metal frame of the tv and probed some of the components for resistance got readings at all the caps I tested including C02. I then changed to the continuity mode with the beep. Every component I touched rang the bell except for C02 and the resistor next to it. Does this make sense?