I was probing voltages on the pins of the TVs Logic board (going to the Time-Control Board) and suddenly it came to life!
The power supply did not sound healthy to me, but maybe I'm mistaken.
I'm trying to get the video uploaded to listen to the sound it makes.

After I power cycled the TV it was was dead once again and I could not reproduce the probing that brought it to life.

Specs:
Vizio LED TV E70u-D3 (70")
Info PDF https://support.vizio.com/s/article/E70u-D3-Model-Information?language=en_US

Original Problem:
It was reported to me that the TV became increasingly unstable.
It would turn itself off after just a few minutes, and there was distortions on the screen.
Finally the TV would display nothing at all.
The power cable was replaced, and the TV was power cycled. Both attempts seemed to correct the problem, however now the white power LED will illuminate for a few seconds and go out after a minute, there is no longer any display shown on the screen.

Trouble shooting Technique.
I intend to check all the power supply capacitors, then move to stand by power, voltage regulators, and voltage levels on other boards.

The red label "12.3V" is the pin I was probing when the TV came to life.

With the TV plugged in, but in stand by mode, there is 0volts on these pins, however after the power button is pressed 4/7 of them get 12.3 volts.
I was checking this when all the sudden the power supply booted up (noisily) and the screen lit up.
I was able to feed a signal into the TV, and it displayed it just fine (just a noisy power supply to my ears)

The 2nd photo shows my diagnostics of the Power Supply.
Pin 13 labeled "PS-ON" has 0 volts in standby mode and 5v when the power button is pressed.
The voltage is persistent on this pin, however the "power" led only stays lit for about 5 seconds before fading out. After witch you can again power it on for a brief time.

I am not sure if the power supply quality is the underlying issue, or if there is a fault on the main logic board.
Can anyone suggest how I can test this?

Thanks!

 

Open run or bad solder joint is my guess. You will need to remove the board and check carefully on the other side. Looks like it is through hole single sided so you are lucky there. Should be easy to fix if you can locate it. Should be at least reasonably easy to find.

A can of freeze spray can also help to localize this kind of problem

Were you pressing on anything while making your measurements?

See if you can localize where the ringing is coming from. Freeze spray can help there too.

 

Bad solder joint sounds right. Whatever you're probing, try resoldering it.

 

Bad solder joint sounds right. Whatever you're probing, try resoldering it.

Open run or bad solder joint is my guess. You will need to remove the board and check carefully on the other side. Looks like it is through hole single sided so you are lucky there. Should be easy to fix if you can locate it. Should be at least reasonably easy to find.

That is a valid theory.
So here is a closeup shot of the terminal in question, tell me what you think.

Here is the top view:

I have some concerns about reworking this connector.
Does this look bad to you? It seems like a good place to start, but I should mention that once working the TV continued to work until I power-cycled it. And I left it alone while I cycled it. could it be that the DMM connected to ground did something, rather than the probe physically restoring the connection?

Another concern is that I may cause a fault. There is a very fine barrier there. (or is that just the solder mask?)
If you still think I should solder it I will, but here is the video of the power supply noise:

A can of freeze spray can also help to localize this kind of problem

Were you pressing on anything while making your measurements?

See if you can localize where the ringing is coming from. Freeze spray can help there too.

Can you elaborate on the freeze spray?
Are you suggesting that I use the trick of finding a short by watching the speed it defrosts?

 

Those solder joints look good to me.

Freeze spray could help the part start working again. The defrosting doesn't do it. It is the freezing. Too bad Radio Shack is closed. They sold those cans.

My hearing is going bad but it sounds like ringing. Very high pitched tone? It has been years since I have done repairs. I am racking my brain trying to remember the cause of that tone. Maybe a member with more recent repair experience can weigh in. If I recall a power transistor that is going bad can make that sound but I might be wrong.

Wow Walmart carries the stuff
https://www.walmart.com/ip/Max-Pro-FR-Blow-Off-Freeze-Spray/21576411

Don't know if they would have it at local stores.

 

Ringing might also just be a harmonic from the switching power supply but again I defer to some of the more learned members.

Supposedly you can use canned air as freeze spray in a pinch. Might be hard to aim.

 

Anyone know how to interpret the values of this Capacitor?
The markings are 1545(M)

 

I expect the capacitance and voltage are written on the other side of the capacitor. The side glued to the PCB

 

I expect the capacitance and voltage are written on the other side of the capacitor. The side glued to the PCB

Murpheys Law.

 

You could look for a resistor used to supply power to start the supply. It will be from the input supply +ve to the switch mode control chip. A common problem is this startup resistor goes high resistance and the supply cannot start. Once the supply is running, the control chip is supplied from a lower voltage generated supply.
And in all thing switch mode supplyish, check the capacity and ESR of the electros!

 

I expect the capacitance and voltage are written on the other side of the capacitor. The side glued to the PCB

Murpheys Law.

You are right, they were, (at least murphy gave me a few the right side up )
they are 25v 1000uF & 450v 100uf respectively. I started removing and testing capacitors:

I won't have access to a proper ESR meter for a few days. In the mean time this is the best I have:

The reading fluctuates between 0.016 Ohms and .31 when I first took it out (maybe too hot?)

You could look for a resistor used to supply power to start the supply. It will be from the input supply +ve to the switch mode control chip. A common problem is this startup resistor goes high resistance and the supply cannot start. Once the supply is running, the control chip is supplied from a lower voltage generated supply.
And in all thing switch mode supplyish, check the capacity and ESR of the electros!

Yeah I'm taking the electros out and testing them, I should have my ESR meter soon which will help.
Interesting theory dendad, A question for you:
Would this resistor issue cause the power supply to run like the video shows?
(if not then perhaps I'm looking at 2 separate issues)

 

Would this resistor issue cause the power supply to run like the video shows?
(if not then perhaps I'm looking at 2 separate issues)

I would not have thought so. And this supply may not start this way.
Test all the caps first I think. They are the most common problem.

 

[QUOTE/]
Would this resistor issue cause the power supply to run like the video shows?
(if not then perhaps I'm looking at 2 separate issues)

I would not have thought so. And this supply may not start this way.
Test all the caps first I think. They are the most common problem.[/QUOTE]

I would agree it's not oscillating correctly, but I could be wrong I haven't had to deal with this stuff for over 30 years now. Yes, the freeze spray can help identify a bad cap we used to do it all the time in the shop. They had a bad run of caps out of china or Korea but all the ones I seen weren't bulging or otherwise duff as they say across the water. Freeze spray may help find a leaky part.

kv

 

I would not have thought so. And this supply may not start this way.
Test all the caps first I think. They are the most common problem.

Ok, I guess this is where the freeze spray can help.

I would agree it's not oscillating correctly, but I could be wrong I haven't had to deal with this stuff for over 30 years now. Yes, the freeze spray can help identify a bad cap we used to do it all the time in the shop. They had a bad run of caps out of china or Korea but all the ones I seen weren't bulging or otherwise duff as they say across the water. Freeze spray may help find a leaky part.

kv[/QUOTE]
Yeah it's easy when you have a "smoking gun" like that or some discoloration due to too much heat.
How did you use the freeze spray?
Did you watch for the capacitor that thaws first as putting out more heat? (Higher resistance)

 

I'm not sure how but, we had a problem with the Quotes so I didn't hit the reply button to your post @Josh Kaufman.

Anyway, it's a hit and miss type thing. But, I had some Samsung Monitors that had some bad caps it was well known. I'm not saying that is the problem, yours do not appear to be a problem and the sound could be anywhere in the power supply. Just hit a cap with the spray listen to see if it changes the sound or you can heat it with a heat gun in an area to see if it gets worse.

Just so you know it was in the secondary of the power supply on the Samsung Monitors, 1000uf caps, I listened to the sound in your video and it's a strange sound I'm really not sure what you got there.

kv

 

I think the sound is caused by the primary side being unstable. What you hear is the frequency/duty cycle variations. Unfortunately it doesn't tell you much about the fault as it could be caused by either primary or secondary side. The capacitors would be a good place to start. After that look at high value resistors on the primary side.