Samsung UN55KS800DFXZA Ver. AA02 with the seemingly common power cycling problem

[nomoresonys]

Re: Samsung UN55KS800DFXZA Ver. AA02 with the seemingly common power cycling problem

[QUOTE=Kilroy2k1;994497]I'm inclined to agree with Davi.p that it is likely a short somewhere on the main board.
Plug everything back in how it should be then let it cycle a few times then feel around the main board for warm areas.
Only feel around the Main Board, Not the power supply board.

***DO NOT FEEL AROUND THE POWER SUPPLY BOARD WITH BARE SKIN OR AT ALL***

I felt it needed to be said.[/QUOTE.

[SoftwareHack]

Re: Samsung UN55KS800DFXZA Ver. AA02 with the seemingly common power cycling problem

In my case, tcon is built into the main board, unfortunately. My problem shows up whether or not the panel is connected to the mainboard or not.

[nomoresonys]

Re: Samsung UN55KS800DFXZA Ver. AA02 with the seemingly common power cycling problem

Oops was getting your tv mixed up with mine again lol, did a quick edit, well that could be why one guy said replacing mainboard would do no good, seems like there would be a way to tell if it was the panel, driver board or mainboard tho with testing.

[nomoresonys]

Re: Samsung UN55KS800DFXZA Ver. AA02 with the seemingly common power cycling problem

In my case, tcon is built into the main board, unfortunately. My problem shows up whether or not the panel is connected to the mainboard or not.

Yes, that makes me think it's the mainboard at fault, because it seems that the on off cycle would stop if the panel or driver board were at fault, when the lvds was unplugged from mainboard, mine does the same thing, even tho I have a stand alone tcon.

[nomoresonys]

Re: Samsung UN55KS800DFXZA Ver. AA02 with the seemingly common power cycling problem

Going to try and test the voltages going from main to tcon with lvds unplugged.

[nomoresonys]

Re: Samsung UN55KS800DFXZA Ver. AA02 with the seemingly common power cycling problem

This freezing is a waste of time, the symptom tells about a short circuit not a software problem. If you wanna to follow funny stories of wine drinkers...
The sh.cir. can be on the panel or tcon, it's hard to see, in general if it is on the panel the adapters on tcon part stops working and TV boots up normally and you can hear a tv channel if programmed..

This appears to be wrong, I just had the lvds cable unplugged, the backlights dont come on but light on the toslink does the same on for 12 off for 2, seems that is isolating the problem to the mainboard.

[Kilroy2k1]

Re: Samsung UN55KS800DFXZA Ver. AA02 with the seemingly common power cycling problem

If you are confident its the main and can make it power cycle, i would switch to the lighter fluid testing. Its non conductive and has a slower evaporation rate then alcohol.
Dribble a bit and use a q tip to spread it around the t con dc/dc converter area and watch for any motion in the liquid as the set cycles. I'f theres any shorted components the fluid will run away from the hot spot.
Continue around all the diff power rail sections till you find the culprit.

[Nick's Tvs]

Re: Samsung UN55KS800DFXZA Ver. AA02 with the seemingly common power cycling problem

Hey, so just had one of these come in the shop with that issue. Thought I would chime in.
This is a panel issue, but rest assured, it's one you can fix.

To proove it's a panel failure and not a main board failure, open the set up all the way down to the address boards, and disconnect the 2 outer boards from circuit.
Turn the TV on. If the cycling stops and you get lines or weird distortion on screen, it will proove that indeed you have a failure with the panel.
If this is the case, look for shorted diodes and burnt resistors on the address boards. It's not technically necessary to replace the diodes, nor the resistors, you can just remove them and TV should boot right back up. We did because we had the parts on hand but if you don't it shouldn't matter. The diodes at fault will be the D5 diodes on the ends and the resitors are the R43 and R44 on both of the edge address boards.

So in conclusion cycling with no picture is not a main board issue but instea is a panel failure. If you do have picture and cycling, then sure main board could be at fault.
Good luck

[budm]

Re: Samsung UN55KS800DFXZA Ver. AA02 with the seemingly common power cycling problem

Hey, so just had one of these come in the shop with that issue. Thought I would chime in.
This is a panel issue, but rest assured, it's one you can fix.

To proove it's a panel failure and not a main board failure, open the set up all the way down to the address boards, and disconnect the 2 outer boards from circuit.
Turn the TV on. If the cycling stops and you get lines or weird distortion on screen, it will proove that indeed you have a failure with the panel.
If this is the case, look for shorted diodes and burnt resistors on the address boards. It's not technically necessary to replace the diodes, nor the resistors, you can just remove them and TV should boot right back up. We did because we had the parts on hand but if you don't it shouldn't matter. The diodes at fault will be the D5 diodes on the ends and the resitors are the R43 and R44 on both of the edge address boards.

So in conclusion cycling with no picture is not a main board issue but instea is a panel failure. If you do have picture and cycling, then sure main board could be at fault.
Good luck

Great info.
So if you disconnect the T-CON or the ribbon cables between T-CON and panel, will this be valid test too? OP did not provide the pictures of the whole back side of the TV to see the board setup.

[SoftwareHack]

Re: Samsung UN55KS800DFXZA Ver. AA02 with the seemingly common power cycling problem

Here's a picture of the backside of the TV. T-CON built into the main board. Tested with panel (and wifi, sound) disconnected at the mainboard with the same power cycling pattern. Also, power board tested with only the backlight (no mainboard) with the backlight staying on. Based on these two results, I limited my focus on the main board. Did I make an incorrect assumption?

(heat sink temporarily removed for checking for hot spots).

[Kilroy2k1]

Re: Samsung UN55KS800DFXZA Ver. AA02 with the seemingly common power cycling problem

I have to agree here, I have done two of these in the past couple of months. One was the diode and the second one was the resistors ( just repaired it this morning).
I was fairly certain the unit rebooted with the LVDS cables disconnected but I am not 100% sure it was the case so I didnt push the issue.
The second one I worked on only had vertical banding which was the result of failed resistors.
Personally I think it fails because in both cases the tvs were set to Backlights 100%, Brightness 100% and contrast 100%.

Hey, so just had one of these come in the shop with that issue. Thought I would chime in.
This is a panel issue, but rest assured, it's one you can fix.

To proove it's a panel failure and not a main board failure, open the set up all the way down to the address boards, and disconnect the 2 outer boards from circuit.
Turn the TV on. If the cycling stops and you get lines or weird distortion on screen, it will proove that indeed you have a failure with the panel.
If this is the case, look for shorted diodes and burnt resistors on the address boards. It's not technically necessary to replace the diodes, nor the resistors, you can just remove them and TV should boot right back up. We did because we had the parts on hand but if you don't it shouldn't matter. The diodes at fault will be the D5 diodes on the ends and the resitors are the R43 and R44 on both of the edge address boards.

So in conclusion cycling with no picture is not a main board issue but instea is a panel failure. If you do have picture and cycling, then sure main board could be at fault.
Good luck

[Kilroy2k1]

Re: Samsung UN55KS800DFXZA Ver. AA02 with the seemingly common power cycling problem

Just for giggles and squirts, lay it down and pop the speaker off, pop the legs and brackets off then remove the metal strip along the bottom that covers the driver boards and take and post a high res pic of both outboard driver boards please.
And while your there try Nicks suggestion to remove the left and right flex cables.

Here's a picture of the backside of the TV. T-CON built into the main board. Tested with panel (and wifi, sound) disconnected at the mainboard with the same power cycling pattern. Also, power board tested with only the backlight (no mainboard) with the backlight staying on. Based on these two results, I limited my focus on the main board. Did I make an incorrect assumption?

(heat sink temporarily removed for checking for hot spots).

[SoftwareHack]

Re: Samsung UN55KS800DFXZA Ver. AA02 with the seemingly common power cycling problem

Here are a couple of pictures of the ends of the panel when I had the metal shield off the other day for a quick visual inspection.

[Kilroy2k1]

Re: Samsung UN55KS800DFXZA Ver. AA02 with the seemingly common power cycling problem

Resistors look ok,
On the very outer ends of the boards you see those little black bits that look like 10 pin devices.
Those are Diode array devices. the center pad on both sides is your common, i think cathode (someone please correct me if i am wrong)
Test with a meter set to continuity between the center pad and the other 4 pads. If any show continuity then you have your problem device.

[SoftwareHack]

Re: Samsung UN55KS800DFXZA Ver. AA02 with the seemingly common power cycling problem

Here's the rest of the driver boards.

[SoftwareHack]

Re: Samsung UN55KS800DFXZA Ver. AA02 with the seemingly common power cycling problem

Currently, everything is buttoned up (except for the back panel). But I'll take it apart again tomorrow (or the day after) to try these suggestions.

I'm wondering how I had the settings. I am in a room with lots of ambient light so I can see having everything turned to the max.

[Diah]

Re: Samsung UN55KS800DFXZA Ver. AA02 with the seemingly common power cycling problem

Nick's he mean by remove the 2 U ribbon cable on the panel boards.... U ribbon used almost with panel which had external T-CON. i don't think this set had it.. but OP can look under the long white tape at the middle of both sides.

[budm]

Re: Samsung UN55KS800DFXZA Ver. AA02 with the seemingly common power cycling problem

https://www.badcaps.net/forum/attach...4&d=1602625575

https://www.badcaps.net/forum/attach...9&d=1602625575

You have two linker cables that you can try disconnecting per Nick's TV.

[Diah]

Re: Samsung UN55KS800DFXZA Ver. AA02 with the seemingly common power cycling problem

OOPS, indeed it had.. time to replace my glasses lol

https://www.badcaps.net/forum/attach...9&d=1602625575

https://www.badcaps.net/forum/attach...4&d=1602625575

[SoftwareHack]

Re: Samsung UN55KS800DFXZA Ver. AA02 with the seemingly common power cycling problem

Well sheeeeet...With the linker cables disconnected to the outer boards the power cycling stopped! I didn't have any source connected so I didn't have any picture, but the fact that the backlight and standby LED stopped cycling on and off, I'm sure the problem is on the panel. Oddly, when I unplug the ribbon cables from the main board, the cycling starts again. I suppose the firmware detects this as a panel fault and starts the reboot cycle?

Now to isolate the particular issue. However, I have a new problem. I forgot that the picture is zoomed 20x or so and my multi-meter probes are too big to check individual pins on the diode array IC. I had ordered some previously, but they won't arrive for a few more days. Visually, I see nothing wrong. I'll post my results when I have more info.

What would be the possible harm in removing one of the diodes without replacing it? I don't have the tools the install (much less remove) surface mount IC's.

Thanks to all for the help in getting me this far. I was convinced that it was the main board...