Noob needing help - Samsung PCB Power Issue

[StaticGSX]

Hello Everyone,

I am new to electronics and still building my understanding of components and fault diagnostics, so I appreciate your patience as I learn.

I have some experience with soldering and have successfully replaced charging and HDMI ports. However, I haven’t ventured into more advanced board-level repairs due to my limited knowledge of component functionality and testing methods. I’ve started reading up on the topic, and I’m hopeful to improve over time.

Currently, I’m troubleshooting a Samsung HDMI monitor that is stuck in a restart loop. I removed the board and inspected it for any visibly damaged components but couldn’t identify any obvious issues.

Here’s what I observed during testing:

1. Top Left Corner (labeled VLED):

There’s a positive test point labeled "VLED" where the voltage fluctuates from 14V (input voltage) up to 40V and back down to 14V in a continuous loop.

The components around this area exhibit the same voltage behavior.



2. Top Right Corner (labeled Panel 5V):

There’s a test point labeled "Panel 5V" where the voltage cycles between 5V and 1.5V repeatedly.

Similarly, the components in this area follow the same voltage fluctuations.


The input voltage at the board remains stable at 14V throughout.

I would greatly appreciate any advice or guidance on diagnosing this issue, as I’m eager to learn and understand what might be causing the problem.

Thank you in advance for your help!

[Faranight]

Hmm, my first thought is that you may have a shorted component (i.e. an SMD cap) somewhere on the board, which is causing the oscillation. A short causes too much current drain on a power supply IC, which overheats and shuts itself off due to thermal protection. After a while when it finally cools down enough, it restarts and the cycle repeats. Can you measure the unpowered board power supply lines (and the coil) in diode mode for a short circuit? If you have a thermal camera, see, if anything is overheating on the board during operation.

[TomWinTejas]

Another trick is to supercool the board by using a can of compressed air turned upside down... then power on the board and whatever component is shorted should thaw much faster than the others.  There are lots of YouTube videos with low cost tips on finding a short like this.

[kripton2035]

by experience, many of the samsung monitors and tvs suffer from a bad flash rom chip. most of the times, a new flash chip solves this boot loop problem.
how old is this monitor ?

[ugawoxoto61]

Hi there! I`m new, and that`s helpful. Thanks a lot!

[StaticGSX]

Hmm, my first thought is that you may have a shorted component (i.e. an SMD cap) somewhere on the board, which is causing the oscillation. A short causes too much current drain on a power supply IC, which overheats and shuts itself off due to thermal protection. After a while when it finally cools down enough, it restarts and the cycle repeats. Can you measure the unpowered board power supply lines (and the coil) in diode mode for a short circuit? If you have a thermal camera, see, if anything is overheating on the board during operation.

@faranight,

Thank you for providing the information. I have saved some videos that I plan to watch tonight on how to test SMD capacitors, which will hopefully help me identify the issue if it is indeed an SMD capacitor. Should it turn out to be a different component, I will then need to research the other components and how to test them for faults.

Currently, I do not own a thermal camera, but I will explore alternative methods to identify the overheating component.

[StaticGSX]

Another trick is to supercool the board by using a can of compressed air turned upside down... then power on the board and whatever component is shorted should thaw much faster than the others.  There are lots of YouTube videos with low cost tips on finding a short like this.

@TomWinTejas,

Thank you for the suggestion. I will definitely look for some videos on YouTube and try them out.

[StaticGSX]

by experience, many of the samsung monitors and tvs suffer from a bad flash rom chip. most of the times, a new flash chip solves this boot loop problem.
how old is this monitor ?

@kripton2035

Thank you for the reply, It’s a fairly old monitor, likely from 2014 or 2016, so any component could potentially be faulty at this point.

The board is inexpensive to replace, but this is more of a learning experiment.