TV standby to power_on circuitry theory and operation

[Crystaleyes]

Although it is far from my main field of interest, people here keep asking me to fix their flat screen TV's.
So far, the problems have generally been on the PSU, the T-Con or the backlights, all of which have been relatively straightforward.
As far as the main board, or SSB, is concerned, the only real issues I've encountered have been bad caps and fucked BGA soldering.

It has also become clear that 'stuck in standby' is a common problem, and something which I no experience with yet could waste lots of time on without an understanding of how the 3v3 is sent to trigger the relay which brings the whole unit to life.

Which leads me to my question, "does anyone know of a good resource which covers the theory and operation of the Standby to P_on circuitry?"

Many thanks in advance

[Biruslapio]

Re: TV standby to power_on circuitry

With no information on model, or board design, there's no universal "follow this" guide when it comes to standby>power on operation, could be anything.

[Crystaleyes]

Re: TV standby to power_on circuitry

That's fair enough.

I'd assumed that there would be some generic form of setup, in a similar way that the ATX power supplies all ground the green standby wire in order to switch the unit on.

From the limited experience with TV's that I have, it certainly seems that most TV's use a similar 3v3 system to activate the relay which powers the backlight and the MCU circuitry.

I suppose I was half-wondering if TV's also grounded the standby voltage?
If you are saying however, that there are many different ways to power-on out of standby, then I clearly have lots of reading up to do.

[CapLeaker]

Re: TV standby to power_on circuitry theory and operation

Nope, not always the case. I guess you can determine if the PSon has power vs not having power. STBY voltage is generated on the PSU and sent to the main board main IC. That’s why a little LED is on on some TV’s. It also power the IR sensor. Once you press the power button, the main board sends PSon and BLon and maybe some DIM signals to the PSU, the PSU turns fully on and the mainboards boots up.
Some PSU’s have a pull up resistor, so the power supply turns on automatically if you disconnect the main board. You can force a PSU a on, by taking a 1k resistor and jumping STBY to PSon, BLon, DIM etc. In these you don’t ground out the PSon pin, you put STBY voltage to it.

It’s a short and crude version and basically all condensed in a nutshell.

[Biruslapio]

Re: TV standby to power_on circuitry theory and operation

I figured they wanted to know another thing, why do TVs gets stuck in stand-by, not how to force psu on, because there's obviously a way to do that, but that too depends on the TV model and can be done without main board, your listed method should work almost always.

The usual reasons a TV can't wake up from STBY if it receives a power-on command via either the button or infra-red AND sends no power_on signal to the PSU, is usually > bad firmware or damaged main chip on the main board, with recent cheap TVs having crap and unreliable firmware they get corrupted from time to time, if it's stored in a non-BGA chip it is easy to re-flash.

[Rajnhl]

Re: TV standby to power_on circuitry theory and operation

sometime voltage regulators, specially passive ones fail. you need good meter to find problem. I have done many local brands in which 3.3v regulator was giving 3.25 to 3.27v volts and board stuck in standby mode.
we are never expert, we master one thing, new technology arrives.

[Crystaleyes]

Re: TV standby to power_on circuitry theory and operation

Hi Rajnhl.

Are you saying that 3.27v is not enough?

[Rajnhl]

Re: TV standby to power_on circuitry theory and operation

Hi Rajnhl.

Are you saying that 3.27v is not enough?

yes . i checked in many local brands

[Crystaleyes]

Re: TV standby to power_on circuitry theory and operation

Thanks.

Good to know for the future...