Reboot cycle on Samsung TV: UE 40D (5700)

[junkpete]

Hey guys,

I hope you help with with my Samsung TV: UE 40D (5700)

A few days ago when I turned it on, it started to reboot every few seconds. This is the loop cycle:

• red LED in front blinks a few seconds (display is black)
• picture appears, sound is playing for about 5 seconds
• everything turns black and the loop starts again

I measured a few caps on the PSU but they seem to be fine. Visual inspection also did not reveal anything suspicious.

When I disconnect the mainboard from the PSU and turn the power on, the background light is constantly on and there is no restart.

I also disconnected everything else from the mainboard to see if something attached to it is causing trouble, but it makes no difference (reboot all every few seconds).

I found the schematics of the PSU here: https://www.electronica-pt.com/esque...-00423a-30427/
But I don't really know where to start the trouble shooting...

One thing which bugs me is the output connection from the PSU to the main board, where I measure 2.1V on pin 13 and 3.1V on pin 15 (while the mainboard is disconnected), although the printed table says "B5V", which I guess should indicate that it's a 5V rail. See here:



I also reset the EEPROM (connecting pin 1 and pin 4 under it and turned it on for half minute), but it didn't help. At least this seems to solve similar issues for a few people.

Any ideas? Is this a bad PSU? But if so, why is the background light working fine when I disconnect the Mainboard? Or is it a firmware issue on the mainboard?

[dick_barton]

Re: Reboot cycle on Samsung TV: UE 40D (5700)

When the power supply is connected to the mainboard and you come out of standby do you have 390V across the two legs of CP814S.

[junkpete]

Re: Reboot cycle on Samsung TV: UE 40D (5700)

Yes I do! It drops to around 375V when the TV reboots and then comes up to 391V again and stays constant until the backlight is off again (and the reboot happens).

[budm]

Re: Reboot cycle on Samsung TV: UE 40D (5700)

Did you remove the connector at both ends, one end is connected to the power supply board, the other end is connected to the main board to see if there is any overheated sign on the connectors?
BTW, if you disconnect the cable between the power supply and the main board, do the backlights stay on when you apply AC to the TV?
https://www.badcaps.net/forum/showth...897#post838897
Please let us know if that fixes the problem or not.

[junkpete]

Re: Reboot cycle on Samsung TV: UE 40D (5700)

Yes, I removed both also both ends, no overheated sign anywhere.

> BTW, if you disconnect the cable between the power supply and the main board, do the backlights stay on when you apply AC to the TV?

Yes, the backlights are then permanently on.

I found a guy in my home town who sells the chip for 30EUR (https://www.badcaps.net/forum/showth...897#post838897), so I guess I will try that next week.

Or are there any other thoughts?

[budm]

Re: Reboot cycle on Samsung TV: UE 40D (5700)

At this point it is the main board problem.

[andytw]

Re: Reboot cycle on Samsung TV: UE 40D (5700)

My rebooting Samsung thread....

https://www.badcaps.net/forum/showthread.php?t=70027

Andy

[junkpete]

Re: Reboot cycle on Samsung TV: UE 40D (5700)

Alright, I replaced the NAND chip by a new one (I managed to get one for 25 Euro) and the TV set has still the same symptoms. I also detached the mainboard and then the lights are permanently on.

Any ideas what to do next? :-/

[ARGO]

Re: Reboot cycle on Samsung TV: UE 40D (5700)

Alright, I replaced the NAND chip by a new one (I managed to get one for 25 Euro) and the TV set has still the same symptoms. I also detached the mainboard and then the lights are permanently on.

Any ideas what to do next? :-/

I have 2 Samsungs with reboot problem too.
I think the problem can be in WT61P805. Do you have it on your board?

[junkpete]

Re: Reboot cycle on Samsung TV: UE 40D (5700)

Yes, this TV has a WT61P805. OK, so I'll replace that too... I'll report back.

[ARGO]

Re: Reboot cycle on Samsung TV: UE 40D (5700)

You can’t just replace it. It has firmware, you must flash new chip.

[dick_barton]

Re: Reboot cycle on Samsung TV: UE 40D (5700)

Are pins 13 & 15 still reading low when the set is powered up and out of standby?

[junkpete]

Re: Reboot cycle on Samsung TV: UE 40D (5700)

You can't just replace it. It has firmware, you must flash new chip.

Damn, I just noticed... I replaced it and now it won't do anything at all when I plug the TV in.

Of course the backlight is on when I disconnect the logic board.

I don't have any tools to flash it. Is it worth to buy the equipment?

[junkpete]

Re: Reboot cycle on Samsung TV: UE 40D (5700)

Are pins 13 & 15 still reading low when the set is powered up and out of standby?

I will check that, I just need to reinstall the old chip

[viktorkane]

Re: Reboot cycle on Samsung TV: UE 40D (5700)

hello friend

write new dump

[viktorkane]

Re: Reboot cycle on Samsung TV: UE 40D (5700)

HELLO

write this dump

Mark:Samsung

Model:UE40D5700

Chassis (main board, components):BN94-04659C

More informations: IC901-24C256

[junkpete]

Re: Reboot cycle on Samsung TV: UE 40D (5700)

Is there a cheap device which can write that dump? I only have programmer for 4/8 and 16 pins...

[junkpete]

Re: Reboot cycle on Samsung TV: UE 40D (5700)

I got a preprogrammed WT61P805 for 10 Euros and swapped that out. I also measured the IC 202 before to check if it regulates to 3.3V and it does (I fed in +5V externally to test it).

So now I am at the beginning... a black screen and no sound (I guess when I reset the main EEPROM, the tuning was reset too).

The current status is:

WT61P805 replaced, IC 202 is OK, main EEPROM reset and also replaced.

Symptoms: red LED blinking for a few seconds, blacklight is on for a few seconds, no picture, no sound and then everything turns off and after a few seconds it repeats.
When I remove the mainboard plug, the backlight is permanently on.

I searched for a working mainboard but all I could find on eBay were refurbishing services which do the same chip replacements.

Or do you have any other ideas?

[viktorkane]

Re: Reboot cycle on Samsung TV: UE 40D (5700)

you are an amateur or a professional
we have 35 years of repairing tv and

[junkpete]

Re: Reboot cycle on Samsung TV: UE 40D (5700)

I am actually a physicist with a decent equipment and a good amount of theoretical understanding (which doesn't help much, haha). I repair all kind of stuff when I find some free time, but I have no professional training, especially not with TVs (this is my first TV project).

I also don't have any deadline since it's my own set

Any hints are welcome.. I am not sure if replacing all kinds of capacitors on the signal board is the way to go now. I could also measure their ESRs but it's quite fiddly and I hope someone with tons of more experience has a good clue where to look next.