Samsung ue49mu6120 No Standby

[Gjackson]

Hi all,

Have a Samsung ue49mu6120 with no standby light,
unplugging mainboard cable from the power supply turns backlight on.

power supply BN44-00807F
Main board BN41-02568B

Some other users suggest that the 25Q40 EEPROM might have become corrupted,
Could someone more knowledgeable take a look and see if mine is corrupted?

Thanks in advance:

[nomoresonys]

Intermittent faults are tough ones if it was intermittent, could be what you soldered did it or maybe there was a bad connection that got better just by unhooking and re-hooking cables, guess just test it for a few hours and see.

[lotas]

Your dump is working.

[Gjackson]

Your dump is working.

Thanks Lotas,

any clues how I should move forward and what to check next?
For testing I have the mainboard and power supply on my bench connected to each other, it seems like 13v is being generated and the mainboard warms up slowly and then after a while it switches into standby mode 8v and I can't find anything wrong with either of them, 3.3v and 1.8v are generated. Right now I don't have the tv chassis to test with, but maybe the wifi module or t-con board is shorted and was shorting the power supply?

[nomoresonys]

Check voltages on CNM803, neg. probe on chassis ground, pos. probe on each pin, read tv in standby=plugged in but power off, take note, leaving probes where they are hit power button, take note of any change, can skip the grounds, report results.

[Gjackson]

Check voltages on CNM803, neg. probe on chassis ground, pos. probe on each pin, read tv in standby=plugged in but power off, take note, leaving probes where they are hit power button, take note of any change, can skip the grounds, report results.

Thanks for the reply, with the two boards set up on the bench here are the readings:



while on standby:

A13V = 8.9v
FAIL_COUNT = 0v
POWER_ON = 0.09v
PWM_BLU = 0v
OD_ON/OFF = 0v
ANA_DIM = 0v

while powered on:

A13V = 12.8v
FAIL_COUNT = 3.3v
POWER_ON = 3.3v
PWM_BLU = 0.04v
OD_ON/OFF = 3.3v
ANA_DIM = 0.08v



I'm assuming pin 1 here spells out FAIL_COUNT because I can't really read it

[Gjackson]

Interesting to note, if I unplug the mainboard from the power supply and take readings again it seems to fluctuate, I don't know if this is intended behavior from the power supply:

A13V = Fluctuating
FAIL_COUNT = 0v
POWER_ON = Fluctuating
PWM_BLU = Fluctuating
OD_ON/OFF = Fluctuating
ANA_DIM = 3.3v

Here's the waveform for A13V when fluctuating:



And for POWER_ON , PWM_BLU, OD_ON/OFF they all virtually look the same as this:



A faint click can be audibly heard with every rise of the waveform coming from somewhere on the PSU

[lotas]

Fluctuations in power supply occur because there is no load at the output...Load it (13v) with a car incandescent lamp.

[Gjackson]

Fluctuations in power supply occur because there is no load at the output...Load it (13v) with a car incandescent lamp.

The lamp lights up fine if the mainboard is also connected:




but when I disconnect the mainboard it blinks and doesn't remain steady:

[nomoresonys]

Diagnosing would be much easier if you had the whole tv.

[Gjackson]

Just a quick update, I did exactly that and got the whole set to test with. Plugged everything back in and now it works somehow, I have standby and the tv powers on. I'm a little baffled as to why it's now working. Owner said that it was being intermittent but when I checked it there was no standby at all. There seem to be no cold joints and I tried tapping the boards while in operation and they seem to keep working. The only thing i've done is resolder the eeprom and replace the thermal paste on the CPU. Any clue as to what I should check before reassembly?

[nomoresonys]

Intermittent faults are tough ones if it was intermittent, could be what you soldered did it or maybe there was a bad connection that got better just by unhooking and re-hooking cables, guess just test it for a few hours and see.

[Gjackson]

I suppose so, in the meantime thanks everyone for the help!

[nomoresonys]

You are very welcome, never a problem helping decent people such as yourself.