Sunday, June 9, 2013

Question about repairing power supply board LG EAY39190301 / PSPU-J702A


I am interested in the following service: REPAIR SERVICE FOR POWER SUPPLY BOARD LG EAY39190301 / PSPU-J702A

With all cables connected, tv flashes 3 blue lights then back to red. With all cables disconnected, once AC is applied to PB it clicks on then right back off. If I just disconnect the YSUS, the tv will power on with audio only, no video.

From the sound of it I would say your power board is working just fine.

As you may know most power supply boards - especially the more powerful ones, which means pretty much all plasma TV power supplies - have several modes of work, most simply categorized by how many circuits are activated to produce output power.
At the bottom is the very low power, always-on standby power supply circuit of +5V or +3.3V.

Then, through a control signal the board is often told to "wake up", which usually involves activation of the power factor correction circuit on the AC side and a bunch of circuits producing bunch of voltages on the secondary side. This is also the stage where the relays click.

And most plasma TVs have yet another stage where the most powerful output voltage - the display sustain one - is being activated and the dreaded Vs is produced.

Power boards have multiple protections built-in in them - the higher the risk - the more and more reliable the protections - and in many cases all you need to find if a plasma power board is faulty is to know if it is capable of producing this last voltage Vs. If it makes it there it's pretty much fine.

And if something gets in the way of producing Vs the power board usually shuts itself down on the way there.

What I am getting at is that the bare symptom that you have a working TV with sound is a very strong indication that your power board EAY39190301 is fine.

And since the sustain board apparently gets in the way of the TV working it's logical to conclude that this is where the problem is.

One more thing on the power boards: some of them - not most, but some - have a programmable ability to turn on all their output circuits when AC is supplied and nothing else is connected to the board.

This is very useful when testing a power board because pretty much all you need to do is pull out all connectors beside the AC power one and supply the AC. If the board clicks on and stays on (and Vs is present, in case of a plasma power supply board) then the board is pretty much fine. Well, apart from load-related or intermittent issues, but both those are fairly rare.

Right now I am not 100% certain if EAY39190301 has such an option and if it does whether it is on or off by default. (if there is, it is always configurable through a controlling pin; it's usually labeled "AUTO").

I am quite certain that your board's cousin (or perhaps brother would be more appropriate) does have such an option and it is ON by default. In other words, when EAY41360901 is supplied with AC and nothing is connected to change the ON signal the board will automatically engage all output circuits and Vs will become immediately available.

Hope this helps!


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