TV Repair: some days you are unlucky...

[amirm]

For the last few weeks our Samsung 4K TV (one of the first that had ever come out) has been acting crazy. Every fifteen minutes or so, it would shut off, then cycle on and off. Letting it cool off would fix it for half hour and then the cycle would continue.

At first I just thought it would be a good opportunity to get an OLED TV to replace it. But then I thought it was simple enough problem that I should fix rather than trash it.

The other option was to keep reviewing gear and ignore it. But then I felt bad that my wife also had to put up with this thing. So decided to work on it.

I open it and isolate the problem to an electrolytic cap. I replace it, put it all back together and it plays for a couple of hours and then cycles off again. I kick myself for not replacing the second cap that was next to it (power supply for the relay circuit). I open it and replace that cap as well.

This time I am smart and don't try to put it back together. I heat it up the affected area well and the SOB power cycles again. I replace the power transistor that was driving the relay and problem remains. Not much else is left other than a few diodes. I cook those with the hair dryer and it shuts off. To make sure it is the diode, I try to heat it up with my soldering iron (common technique for finding thermal issues down to a component).

I reach out with the heated tip of my soldering iron without good sight and bam, it hits one lead on the diode and a massive, 1 inch spark greets me. I could not believe the nature of this short given the tiny low power circuits involved. I see nothing that has blow up including all the fuses. But there is this horrible smell of burnt electronics. Take the board out and look on the other side and the horror unveils: a bunch of surface mount parts including an opto-coupler IC had blow to pieces. It was so bad and the insulation on the back on the chassis of the TV had a hole punched through it!!!

I was so close to having this TV working for just a few parts I had around the lab. Now I have this massive power supply board shot to hell and no way to repair without schematic and ton of troubleshooting. This is what the beast looks like:

It has huge number of parts on the other side that are surface mount.

I search for a replacement board and no one has it in stock. And the few that have prices are in $220 range plus shipping. This was a $4,000 TV when it came but definitely not worth a fraction of that today.

Then by magic, I find this TV Part place that has 11 in stock and is selling them for just $51!!! I check out the company and it seems legit. So put in the order and spent $22 for 2 day shipping.

Praying there is no hardware revisions that make the thing not work with the first production unit I have.

Anyway, I was so close, so close to getting the thing working and then this setback. So I figure I vent and share the ordeal with you all.

I know the world has bigger problems but right now, this darn TV is on my mind. Keep trying to turn on the TV and then realize nothing is there!

May your hardware troubleshooting go better than mine.

 

[digitalfrost]

Samsung TVs are notorious for ****** caps.

 

[oldsysop]

 

[direstraitsfan98]

They just don't make them like they used to.

My baby is 20 years old, it will probably last another 60 years at the current rate I use them. Wouldn't be surprised if they out live me. I'd take better pics of the internals but every single section of it has a metal cage around it. Amazing build quality. Sony made the best televisions in the world...

 

[Dimitri]

Then by magic, I find

Some have it, some don't

 

[bigx5murf]

My Samsung tv was a 2013 black Friday pickup. 2 years ago while my wife was watching, it looked like a black waterfall suddenly took out the picture. I followed a YouTube troubleshooting guide, and it said t-con board failure. I found a t-con board from the company that made the video. When it came in I started disassembling the TV, and it was immediately apparent why the board failed. There were 3 thick thermal pads that allows the 3 chips on the board to use the chassis as a heat sink. All 3 pads were crooked and covering less than half the chip surface area. The TVs been working ever since.

 

[Deleted member 9286]

I always remember back in the day, pre plasma and LCD, people always said “don’t ever open up and mess about with your TV, even if it’s been unplugged for a couple of days, there’s still some electrical components with enough charge to kill you”.

I assume there was some truth in this?

And does it still apply to modern TVs? Amir’s post got me thinking about this, I had forgotten all about it.

 

[mansr]

I always remember back in the day, pre plasma and LCD, people always said “don’t ever open up and mess about with your TV, even if it’s been unplugged for a couple of days, there’s still some electrical components with enough charge to kill you”.

I assume there was some truth in this?

That would be the high-voltage supply for the CRT, typically 20-30 kV (around 1 kV per inch of screen size). They usually had some very large capacitors operating at a few hundred volts. These could retain enough charge to give you a good zap for a quite a while. Proper procedure when opening the case was to discharge any such capacitors using a suitable resistor before doing anything else. Of course, some repair jobs would require running the thing with the case open. In those instances, you just had to be very careful.

And does it still apply to modern TVs?

No, everything in a modern TV is low-voltage. The power supply still handles mains voltage, of course, but there are no enormous capacitors holding lethal voltages any more.

 

[mansr]

I reach out with the heated tip of my soldering iron without good sight and bam, it hits one lead on the diode and a massive, 1 inch spark greets me. I could not believe the nature of this short given the tiny low power circuits involved. I see nothing that has blow up including all the fuses. But there is this horrible smell of burnt electronics. Take the board out and look on the other side and the horror unveils: a bunch of surface mount parts including an opto-coupler IC had blow to pieces.

The opto-coupler was probably the feedback path for switching regulator. The diode you touched may have been a rectifier for the mains input. Shorting that to ground would make some sparks even if the normal current is low.

Can we have a pic of the damage, please?

 

[solderdude]

Most TV repairshops these days simply swap boards. Only when some specific parts are known to become defective these will be replaced on component level.
The repair business surely has changed over the years....
I am glad to have 'gotten out' about 20 years ago.

 

[Deleted member 9286]

That would be the high-voltage supply for the CRT, typically 20-30 kV (around 1 kV per inch of screen size). They usually had some very large capacitors operating at a few hundred volts. These could retain enough charge to give you a good zap for a quite a while. Proper procedure when opening the case was to discharge any such capacitors using a suitable resistor before doing anything else. Of course, some repair jobs would require running the thing with the case open. In those instances, you just had to be very careful.


No, everything in a modern TV is low-voltage. The power supply still handles mains voltage, of course, but there are no enormous capacitors holding lethal voltages any more.

Thanks @mansr very informative.

 

[DonH56]

TV tubes (CRTs) used to ship with a clip that shorted them out during transport. They could easily charge to several kV from static electricity during packaging and removal. I still have a scar (and bad memory) of pulling a new CRT out of the box and my arm brushing the anode where the clip had fallen off during shipping. Shock, zap, dropped the tube and it imploded at my feet. Not a pretty sight.


Amir -- Quite a saga, but after that we really need pictures of the backside destruction to properly laugh at commiserate with you. Hope the new board takes care of it!

 

[mansr]

TV tubes (CRTs) used to ship with a clip that shorted them out during transport. They could easily charge to several kV from static electricity during packaging and removal. I still have a scar (and bad memory) of pulling a new CRT out of the box and my arm brushing the anode where the clip had fallen off during shipping. Shock, zap, dropped the tube and it imploded at my feet. Not a pretty sight.

How much energy are we talking about here? Enough to be dangerous or just unpleasant?

 

[Koeitje]

If you ever run into issues with the videoboard its most likely due to solder connections breaking apart and not the caps. Just grab the board and heat it in the oven for a while to reflow the solder. Fixed my dad's tv 4 times in a row and got him 2 extra years from it.

 

[DonH56]

How much energy are we talking about here? Enough to be dangerous or just unpleasant?

The voltage is high (typ. 20 - 30 kV) but very low current (mA) so it is more of a surprise than anything else. Not even all that painful; that usually comes from the reaction -- I have several scars from where I jerked my arm away from the shock and sliced it or my hand on something in the TV set (or radio, whatever). The big danger is because you often have one hand resting on the chassis someplace while getting something else in or out so the charge goes through your chest and disrupts your heart or other vital organs. I don't know how common that was, but I did put my CPR training to use when a fellow tech suffered a heart attack after a "mild" shock.

It takes about 3 kV or so before we can even feel a static shock, and 10 kV is not uncommon from shuffling across a rug and touching a doorknob, so it is something like that. In my world, static discharges of from 10's to 100's of volts can destroy components and test equipment, so our anti-static procedures are pretty rigorous.

 

[peanuts]

putting stuff in the oven does not reflow the solder

 

[DonH56]

Maybe on the cleaning cycle... But I thought 60/40 solder melted around 190 degC (~370 degF)? An oven should be hot enough, though the idea of reballing a component that way gives me shudders. Some balls are not soft solder and have much higher melting points, intentionally, as do most lead-free solders.

 

[amirm]

Amir -- Quite a saga, but after that we really need pictures of the backside destruction to properly laugh at commiserate with you. Hope the new board takes care of it!

The drama is mostly gone because I had to clean up the charred area to get rid of the terrible stench. But maybe you can still see the damage:

First look in the black area and notice the large area that is charred. And a spot left of it that has shot through that protective layer.

The PCB area I have circled is where parts were blown up bad. The opto coupler is at 3:00 o'clock as indicated by the slot under it for isolation. There are a bunch of other parts turned into charcoal that are too tiny to see (resistors, transistors, etc.).

 

[Koeitje]

putting stuff in the oven does not reflow the solder

Why did it fix the issue then?

 

[mansr]

Maybe on the cleaning cycle... But I thought 60/40 solder melted around 190 degC (~370 degF)? An oven should be hot enough, though the idea of reballing a component that way gives me shudders. Some balls are not soft solder and have much higher melting points, intentionally, as do most lead-free solders.

63/37 solder melts at 183 °C. 60/40 is non-eutectic and is fully melted at 190 °C. Lead-free solders generally melt somewhere around 220 °C. Although a regular oven gets hot enough, there is a risk of damage since it certainly won't be following the proper temperature profiles.