What fails on TFT power boards? 3

[NFI]

Hello,

I've been given a Viewsonic VA2010wb screen that is apparently dead. Although I get a dim orange light at the power LED, I get no video output at all (no backlight and no OSD, either) and there's a nasty high-pitched whistle which sounds like a capacitor going through its death-throes.

Does anybody know what tends to fail on these TFT power boards? I'm pretty certain that's what's failed, but I can only seem to get a replacement board from the US for $60 plus. I've read on the web that some of these replacement boards have upgraded capacitors, so if I replaced all the capacitors on the board I've got, what are the chances of it suddenly working afterwards?

The board part number is FSP043-2PI01F - unfortuntely there's nothing obviously blown on it, so I'm a bit in the dark trying to figure out if it's even the part at fault...

Any help would be much appreciated,

Thanks

 

[paparazi]

Power invertors.......

On wings like angels whispers sweet
my heart it feels a broken beat
Touched soul and hurt lay wounded deep
Brown eyes are lost afar and sleep

 

[NFI]

Do you mean the voltage regulators?

I'm not sure which bit you're referring to as a power invertor...

Thanks.

 

[BadBigBen]

For clarification:

The board part number is FSP043-2PI01F = power inverter...

so if I replaced all the capacitors on the board I've got, what are the chances of it suddenly working afterwards?

only one way to find out... replace them...



Ben
"If it works don't fix it! If it doesn't use a sledgehammer..."
How to ask a question, when posting them to a professional forum.
Only ask questions with yes/no answers if you want "yes" or "no"

 

[NFI]

Well I did change them...and it made no difference, so something else has obviously kicked the bucket.

Are you sure this board's an invertor rather than a rectifier? SMPS invertors convert DC to AC...this board, I thought, was doing the opposite - rectifying AC to DC...it certainly has an AC input and, as far as I'm aware, TFT's are DC components. Have I got this whole thing arse-about-face?

 

[tf1]

If you look at the TFT screen in dim light, can you see a very faint ghostly image? If you can, it confirms that your screen is OK.

This points to either the Inverter or the CCFLs (cold cathode fluorescent lamps) have failed. The 'screaming' noise suggests it is the inverter and this is a common failure, especially on laptops.

The inverters were never built to be repaired - only replaced. But balance the cost of the replacement against the low cost of a new 20" TFT with a 3 year warranty. And if you replace it with a 20" with a DVI socket, you'll get better performance too.


Regards: Terry

 

[NFI]

Thanks for that.

Again, I'm not sure what you're referring to as "the invertor" - do you mean the whole power board? The screaming sound, to me, suggested over-voltaged capacitors and, when I examined the board, there were three capacitors with domed end-caps. I replaced them (uprating from 10V to 25V) but still have the same problem - i.e. I get the orange standby light, but nothing else.

I know switch-mode power supplies aren't *meant* to be repaired (or even repaurable), but people obviously do, as you can buy them in the US on ebay...it must be possible to fix it myself, but I just need to try and figure out what's wrong with it...

Thanks.

 

[tf1]

An inverter is the circuitry that takes the 12 - 18vdc (or whatever) from the main dc supply and converts it to a high AC voltage required by CCFLs. The striking (starting voltage) may be 500 - 600 vac and the running voltage 300 - 400 vac. One huge advantage of the new TFT screens with LED backlights is the removal of the vulnerable inverters and limited life CCFLs. Theoretically, LED backlit screens should last many years beyond CCFL lit displays.

Having previously stated that screaming noise suggests the inverter, it may be screaming because it is off load and free running (the connection to the CCFL is broken or the CCFL is open circuit) rather than it is broken.


Regards: Terry

 

[NFI]

Ah, I see - thanks for explaining that.

I don't get a dim image on the screen, so I don't think the CCFL's are lighting up, but I also don't think the TFT itself is powering up...

Perhaps you're right and, even though this screen was given to me for free, it's still not worth the bother and expense of repairing...

ho hum...

Thanks for your help...

 

[tf1]

Even with a dead CCFL/Inverter, if you look carefully at the display you should see a ghost image. This suggests something more serious. Without knowledge of the TFT in question, I think finding the problem could be very difficult. It may be worth just checking around it to make sure that a ribbon connector hasn't dislodged or something else easy to spot. Otherwise I'd recycle it.


Regards: Terry

 

[paparazi]

No stars but at least I broke the 17day silence lol.

On wings like angels whispers sweet
my heart it feels a broken beat
Touched soul and hurt lay wounded deep
Brown eyes are lost afar and sleep

 

[BadBigBen]

in that case... have one from me...

Ben
"If it works don't fix it! If it doesn't use a sledgehammer..."
How to ask a question, when posting them to a professional forum.
Only ask questions with yes/no answers if you want "yes" or "no"

 

[NFI]

No, you're quite right, you did type the word "invertor" there...here's a star from me too, well done!