Samsung TV internal PSU voltage

[DrOnline]

Hi everybody. I'd like your input on my reasoning.

The TV in our office meeting room stopped turning on. It's 100% dead. Nothing happens when we try to turn it on. Plugging in the power doesn't turn on any LED's or anything. Pressing physical power button gives no result. It has been replaced, so they wanted to throw it out, and I figured: I don't have a TV at the moment, let me take a look at it.

I pop it open, and I see there is a yellow power supply PCBA, and a green PCBA, presumably doing everything dealing with running the panel and controls and everything. Visual inspection of either PCBA gives no clues. Nothing sooty and no obvious burned holes on chips or anything. They might be there, but I couldn't see any.

I connect the 230V power cable. The silk screen print on the yellow PCB says it should output 13V through that black cable with the orange connector. I measure, and it's only 11.5V. So I disconnect 230V, disconnect the cable between the two PCBAs, reinsert 230V and measure again, now it's 13V on the PSU output side, and the backlight is enabled across the entire TV panel. I conclude this means the green PCB has a problem (visual inspection gave no clues), so I stopped there and ordered a replacement green board. Used one, from Ebay...

Do you agree with this logic? Do you agree that if the voltage drops from 13V to 11.5V it suggests there is a problem with the green PCBA? Do you agree that simply replacing the green board seems likely to work without any further issues?

By the way, the black boxes are the speakers. No wonder audio isn't great on flat screen TV's. And the picture is upside down. The top of the picture is the bottom of the TV.

PS: I can't find the remote. I can google this, but quick question: Anybody know if it's manageable to "pair" a remote from a different TV to this one...? Just in software menus, I mean.

[Greybeard]

You can try to buy a clone remote control on ebay, amazon etc. or just buy a universal remote control that can be matched to the specific Samsung model. Mostly matching is done by entering a code number for the model/manufacturer but there are also RC the can be connected to PC per USB and configurated by PC tool.

[Shock]

Samsung remotes can work across different models (no idea about exact compatibility).

There are a few parts - power board, back lighting cable, processing board, panel (which has back lighting and some lcd drivers), then the panel/signal cables (that go to the timing controller on the processor board).

Probably one of the last three but you could have perhaps disconnected or alternated signal cables to see if it was the cables or a bad driver/panel issue.

[DrOnline]

Yeah maybe ordering the replacement was premature.. We'll see what happens. I'll update when I receive it

[wasedadoc]

I had no difficulty finding and buying on ebay an official Samsung remote that was an exact replacement. A bit more expensive than the compatibles but all functions giaranteed to work. Granted I did have the original which had the remote model number on it.

[Veteran68]

The fact that the power supply board's output is dragged down to 11.5V when the logic board is connected indicates a short or other low-impedance fault on the logic board. If you have a thermal camera handy it might highlight the culprit, which will often be a bad SMD capacitor, diode, or maybe a mosfet.

So I disconnect 230V, disconnect the cable between the two PCBAs, reinsert 230V and measure again, now it's 13V on the PSU output side, and the backlight is enabled across the entire TV panel.

I would expect the backlight to be powered at higher than 13v (usually 24v, 48v, or 96v) from a boost circuit on the logic board, which I expect is what those JST connected cables at the top right (which looks like bottom left) of the TV are providing. So my question is, if you disconnected the cable from the power supply board to the logic board, how could the backlight be on?

[DrOnline]

Very reasonable question. I'll see what I can find out tomorrow, I'm still curious. Waiting for the shipped pcba now, but let me check what you asked.