Samsung 55 inch t.v. power board not working

Thread Starter

Junior DIYer

Joined Jul 8, 2020
3
Recently new to the site, and babyfaced to working with circuit boards. Father in law was going to throw out a 55 inch t.v. and made a comment that the power board was the issue and that it would be an easy fix.

Took the t.v. apart and found that the power board had been worked on before from the look of things. Being relatively new with no formal schooling, so I don't even know what to call what I'm looking at.

What looks to be a larger chip looking piece under a heat sink was the first issue I saw. Based on the fact that the standby light on the tv still shows up when you plug it in, I'd say that's my best bet. There looks to be two capacitors as well that have some.of the insulation worked away by something, so I'll try and replace those as well.

Absolutely any advice would be amazing. If I am or am not looking in the right area, best practices etc. I've got a soldering iron, wick, flux, solder, digital micrometer, etc. I've also looked up a bunch of videos, but the general practices to fix it seem all over the place. Any clarity on best ways to go about this project?
 

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Zeeus

Joined Apr 17, 2019
598
Here's a voltage testing I learned to check if problem is from SMPS or not

After replacing capacitor and checking bridge and diode are ok and same problem

Standby voltage is ok you typed.

Voltage test : Firstly, don't add the connection for the backlights

From the "standby voltage pin", solder a resistor (1k - 10k) from it to the "Power on pin"

After, check the pins for 24v and 12v if they are ok
 

Thread Starter

Junior DIYer

Joined Jul 8, 2020
3
I've checked all the capacitors, and other than the ones that have stripped insulation, they seem fine. My biggest issue is the soldered connections for the pieces I want to remove don't seem to want to budge. Iron is working properly, and a small amount comes off, I'm more worries that the solder has oxidized and the board may be a write-off.
 

abrsvc

Joined Jun 16, 2018
39
In the third picture there is an IC that looks like it is missing a part. I would start there. I couldn't read the numbers on it. If you can take a better picture or one closer so we can read the number, I would start there.
 

DarthVolta

Joined Jan 27, 2015
501
Usually these types of things will have a mini SMPS, like a 12V wall-PSU, that provides low voltage power to chips on the primary/hot side of the PSU, and also power another transformer winding, that powers the 5V STBY pwr (5V is very common STBY PWR), and chips, on the output/coldside of the main PSU.

So it's a good bet the mini-SMPS is working fine, and the problem is farther along.
Somewhere, sometime, some chips is probably detecting a problem, like some voltage or current too high or low, and something shuts down.

So I'd check what controller chips in the PSU have PWR, then start seeing what the HV PSU section is doing, or being told to do, by the controller chips.
 
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