Samsung 4K UN55NU7100F stuck in a reboot loop

[Yanleb]

Ok, I have this Samsung 4K UN55NU7100F that is stuck in a reboot loop.

I know this is not a backlight issue since when I disconnect the power cable from the main board the power supply starts and the backlight is working just fine. Each of the 6 LED strip connectors measure 116 volts.

I've found that when I disconnect any one of the two LVDS cables going from the main board to the LCD panel (it doesn't have a T-CON board) it is working just fine (with no picture as you can expect).

On a few occasions I found that reconnecting the disconnected LVDS cable while the TV was still on allowed it to run with a very good picture. It allowed me to perform a factory reset, update the firmware and so on. But as soon as I power off the TV and try to power it on again it is still stuck in a reboot loop.

The rest of the time when powering on the TV with one LVDS cable disconnected, then reconnect it (while it is still on) will cause it to reboot after a few seconds.

The main board PCB model is BN41-02635B. This main board design is used in many TV sets:
UN40NU6070FXZA
UN40NU7100FXZA
UN40NU7100FXZC
UN40NU7200FXZA
UN43NU7100FXZA
UN49NU6300FXZA
UN50NU7100FXZA
UN50NU7100VXZA
UN50NU710DFXZA
UN50NU7200FXZA
UN55NU7100FXZA
UN55NU7300FXZA
UN58MU6070EXZA
UN65NU7100FXZA
UN65NU7200FXZA
UN65NU7300FXZA
UN65NU730DFXZA
UN65NU740DFXZA
UN75NU7100FXZA
UN75NU7100FXZC
UN75NU7100FXZX
UN75NU710DEXZA
UN75NU710DFXZA
UN75NU7200FXZA

Another revision BN41-02635A of that PCB design is also used in the following TV sets:
UN40NU7100FXZA
UN43NU7100FXZA
UN43NU710DFXZA
UN50NU7100FXZA
UN50NU7100VXZA
UN50NU710DFXZA
UN50NU7200FXZA
UN50RU7100FXZA
UN55NU7100FXZA
UN55NU710DFXZA
UN55NU7200FXZA
UN55NU7300FXZA
UN58NU7100FXZA
UN58NU710DFXZA
UN65NU7100FXZA
UN65NU710DFXZA
UN65NU7300FXZA
UN65NU7300FXZC
UN65NU740DFXZA
UN75NU7100FXZA
UN75NU7100FXZC
UN75NU7100FXZX
UN75NU710DEXZA
UN75NU710DFXZA
UN75NU7200FXZA

When removing the metal cover at the bottom of the TV set I can easily do voltage measurements. The problem is that the majority of the test points have no meaningful labels like TEST1_2, TEST1_3 and so on.

Do you have suggestions on what to check next?

Thanks.

[Davi.p]

Re: Samsung 4K UN55NU7100F stuck in a reboot loop

On the panel's distribution boards sits probably the problem, locate the possible diodes, one can try remove them, also try locate the avdd trace from main board, mask it and connect it through a power potentiometer, try until the screen turns on, locate some odd warm on the screen caps.. last, try insulate some pins on the ribbon cables until it stays on, if you own oscilloscope mask only clock lines