Samsung LE40C535 dead mainboard

[PowerAmpFreak]

Samsung LE40C535, mainboard appears dead.
Powersupply operates correct outputting +5.2V STBY supply to mainboard.
No action from either front buttons or remote.
Standby led doesn't come on.
Front touch button board recieve 3.3V and signal wires is alive when touching buttons.
In some way the mainboard does not want to play.
Any advice what to check on the complex mainboard?

[tom66]

Re: Samsung LE40C535 dead mainboard

All the voltage regulators.
BN96-xxxxx number?

[PowerAmpFreak]

Re: Samsung LE40C535 dead mainboard

all the voltage regulators.
Bn96-xxxxx number?

bn94-02616

[randtek]

Re: Samsung LE40C535 dead mainboard

Disconnect the cable that goes from the power board to the main board. Plug the TV in, and see if the power supplies come up, and the backlights light. If so, this will prove (for the most part) that the power board and backlights are working. This is a great quick check on Samsungs, to narrow your problem down to the main board.

[PowerAmpFreak]

Re: Samsung LE40C535 dead mainboard

Disconnect the cable that goes from the power board to the main board. Plug the TV in, and see if the power supplies come up, and the backlights light. If so, this will prove (for the most part) that the power board and backlights are working. This is a great quick check on Samsungs, to narrow your problem down to the main board.

Thanks, already tried that and powerboard start and backlights on.

[retiredcaps]

Re: Samsung LE40C535 dead mainboard

Did you test and report the measurements for the voltage regulators as tom66 suggested?

[PowerAmpFreak]

Re: Samsung LE40C535 dead mainboard

Did you test and report the measurements for the voltage regulators as tom66 suggested?

Not yet, but will look deeper into this tomorrow.
During standby, the power consumption is kept so low (below 0.5W from 230VAC) so there seems to be only one regulator alive at this point. I already verified the small touchbutton front board has proper supply of 3.3V so I assume this is also used to keep the processor alive in standby mode.

[PowerAmpFreak]

Re: Samsung LE40C535 dead mainboard

As fas as I can see, the only voltage from psu available at mainboard is +5.2V STBY and this is regulated down to 3.3V by *some* of the local mainboard regulators.
The bigger regulators are all shutdown, having no input voltage since the main 5V and 13V are switched off at the powersupply.
Pulling the connector CN802 (PSU) force the backlight on and all the other psu voltages to come alive.
So the mainboard is put into sleep, wonder how to wake it up.

[PowerAmpFreak]

Re: Samsung LE40C535 dead mainboard

BTW, is there possibly a dedicated low power microcontroller handling standby operation?
Or could this be done by the main processor, if clock frequency is turned way down to save power during standby?

[tom66]

Re: Samsung LE40C535 dead mainboard

There is usually a SUB MICOM on older Samsung TVs that can hold the main processor in reset. I was once stuck with an LE32N73BD main board with a reset problem, when I disabled this the TV just displayed noise, so it appears the SUB MICOM must send some initialisation commands first.

[PowerAmpFreak]

Re: Samsung LE40C535 dead mainboard

Is there any way to force the mainboard in some kind of factory reset state, reinitialize EEPROM memory and so on?
The service manual does not cover this at all, and will probably need an external programming jigg hardware.

[vinceroger69]

Re: Samsung LE40C535 dead mainboard

dont know if this may help
http://wiki.samygo.tv/index.php5/UnB...LExxC550.2F530

[PowerAmpFreak]

Re: Samsung LE40C535 dead mainboard

dont know if this may help
http://wiki.samygo.tv/index.php5/UnB...LExxC550.2F530

Thank you, interesting reading!
I will try to mess up the I2C communcation and force the set to rewrite the EEPROM. I'll update the results.

[vinceroger69]

Re: Samsung LE40C535 dead mainboard

may be worth a try its up to you. can you get a blank eprom for these and would it re write the eprom on start up? i have never dealt with eproms at all myself factory reset is as far as i would go.

[PowerAmpFreak]

Re: Samsung LE40C535 dead mainboard

I wonder if, after all, the powersupply could be faulty in some way.
I have confirmed that pulling the cable between mainboard and psu will operate the psu and turn on backlight.
Since in my case, the standby led doesn't turn on, may indicate that sets actually believe it's in operating mode, still the PS_ON signal is low, it should be pulled high from mainboard to let powersupply start. (This is what happens when pulling the cable).
Well, this story will continue.

[JesusHCU]

Re: Samsung LE40C535 dead mainboard

Hello,
Did you have solved the problem? I have the same problem in the same boards.

[senndogg]

Re: Samsung LE40C535 dead mainboard

This is becoming very common for LEXXC500 series. Today I had my fourth or fifth case in my workshop and till now i have managed to swap boards with used ones from ebay. In my first 2 cases i went into deep when trying to read/reset different EEPROMs, checked LDOS but no success. Customers claimed it all happened when plugging/unplugging main AC cord.
I always checked the psu by disconnecting and waiting for the backlight.
Till now, everything has worked with the ebay boards. I have no other ideas.