TV Repair - Accidentally brought to life (momentarily) with DMM!

Other Hardware General Electronics
1

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 VIZIO Support

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!

2

And what has this got to do with Arduino?
It is common knowledge that TVs stop working after a few years because of bad caps.
If you're lucky you find one with a bulging top.
If not, use an ESR meter and test every cap (especially in the power supply).
Leo..

3

joshsstuff:
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?

One test is to get a new (and known to be working) power supply board. That'll narrow things down.

4

The best tool to see if it's caps is a hair dryer.
Turn the TV off at the wall, and warm the whole supply (nothing else) for 10-minutes with the hair dryer.
Then see if the TV works.
Leo..

5

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


6

Possibly 470 microfarad, like the others. You might have to look on the other side of the capacitor to confirm it.n

The forum title General Electronics doesn't make it obvious...... but it's related to general electronics involving projects associated with arduino.

7

Southpark:
The forum title General Electronics doesn't make it obvious...... but it's related to general electronics involving projects associated with arduino.

Indeed, and there is probably a 'Help me fix my TV' forum somewhere.

8

Try Repair - Page 1
In the past EEVBLOG has had a number of videos and conversations about TV/Monitor repairs, ESPECIALLY WRT flakey power supplies.

9

westfw:
Try Repair - Page 1
In the past EEVBLOG has had a number of videos and conversations about TV/Monitor repairs, ESPECIALLY WRT flakey power supplies.

Ok, I will, thanks.

10

If you cant find any swollen capacitors, usually its the output ones, have a close look on the primary side of the switcher for a hi value resistor (usually 100K or more ) which may appear burnt or has gone open.
This resistor is needed at start up to make the switcher start and if they go open then the switcher will not start properly.
Sometimes prodding around with a multimeter is enough to simulate the resistor and the power will start.

11

Good point. I replaced hundreds of those startup resistors in VCRs and TVs in the nineties.
But I think they have that sorted now with this generation of supplies.

OP, don't go replacing caps randomly. You might introduce a second fault.
Get an ESR meter if you want to do these repairs yourself.
Leo..