22 inch LCD.

[AtomSoft]

Ok i think i found the problem... Huge burn spot on opposite side of these parts (in picture)

But what part are they? They have writing but google hates me lately.

 

[Nigel Goodwin]

Just because the PCB is discoloured doesn't mean those parts are faulty - it's FAR more likely they are perfectly fine.

I would imagine they are some kind of FET though?.

 

[jpanhalt]

If they are mosfets and assuming GDS pin sequence, what is/are the through hole component(s) between the drain of one and the source of the other? Is it part of a switching supply?

If so, then the question becomes what made them overheat?

John

 

[Nigel Goodwin]

If they are mosfets and assuming GDS pin sequence, what is/are the through hole component(s) between the drain of one and the source of the other? Is it part of a switching supply?
If so, then the question becomes what made them overheat?

You're assuming they have actually overheated? - it's perfectly normal for the rear of the heatsink PCB to be somewhat discoloured.

 

[jpanhalt]

True, but AtomSoft described them as huge burnt spots. I originally had made my comment about overheated conditional, then decided a little simplification can avoid a lot of words.

The real issue is to fix the display. If AtomSoft thinks there is too much heat being generated in these devices, then that is where I would focus on the "why." I do agree the devices, if mosfets, are probably a symptom, not the cause.

John

 

[AtomSoft]

Thanks guys ill get back here after work with more info. The monitor doesnt turn on at all. No power light. But all fuses are fine and power is on the main power PCB but some lines on secondary control pcb says 12v but has no power. The rest of the board looks perfect so i assume a DARK burning orange spot is a good place to start.

I think a power spike from either a blackout or something could have caused this whole monitor to die. Ill take some more pictures so i can follow all traces better and ill let you guys know whats going on ok. Thanks again for the advice.


Ok The burn spots are darker than in picture but flash is so good. Also the through hold parts are jumpers (WJ7) and that 1117 part has no power at all. So i assume a power supply issue is the main cause. I think regardless if the monitor is off or on as long as its plugged in it should have power since the main cpu controlls the LED(power) and buttons. So with no power coming in there no power for lcd control side

 

[Nigel Goodwin]

Thanks guys ill get back here after work with more info. The monitor doesnt turn on at all. No power light. But all fuses are fine and power is on the main power PCB but some lines on secondary control pcb says 12v but has no power. The rest of the board looks perfect so i assume a DARK burning orange spot is a good place to start.

Sorry, but that's an assumption from someone who doesn't repair TV's professionally

Boards (particularly in cheap make sets) commonly get discoloured in that way, it only very rarely is anything to do with the fault.

There are usually two separate power supplies on these sets, the main one and the standby one (usually either 5V or 3.3V) - the standby one runs all the time and supplies the micro, which in turn switches the main PSU ON and OFF. A fairly common fault is leaky rectifiers in the standby PSU - but just check the output voltage from it.

 

[jpanhalt]

Those green caps in the background look puffy in the picture. One of my Samsung 213T's went belly up and replacing six, similar looking caps is all it took. None of the caps had actually popped yet.

John

 

[Nigel Goodwin]

Those green caps in the background look puffy in the picture. One of my Samsung 213T's went belly up and replacing six, similar looking caps is all it took. None of the caps had actually popped yet.

Yes, those six capacitors are all faulty - an ESR meter would be needed to test them, but any capacitor bulging like that requires replacing anyway.

High-ESR electrolytics is by far the biggest cause of problems in modern electronics. You should replace them with 105 degree ones from a decent manufacturer.

 

[duffy]

Yeah, those caps. Looks like you can even see brown crud residue from the electrolyte. Replace all six.

 

[Nigel Goodwin]

Yeah, those caps. Looks like you can even see brown crud residue from the electrolyte. Replace all six.

It 'might' cure it - but sometimes the failure of the capacitors causes further damage. But obviously it's the first thing to do.

 

[AtomSoft]

Ok thanks guys, ill add it to my mouser order today.

 

[AtomSoft]

Nigel these are: 105c .. 470uF 25v... 10mm Dia, 15mm tall... (the ones that are bad)

I dont know Cap manufactures besides a couple but at $0.23 each they have to be OK at least... from Nichicon:

https://www.mouser.com/ProductDetai...=F1FIHXGaVFnggAw6tdO7l3YoQY0xQK9sT13FBbd8I4E=

 

[nickelflippr]

Look for low esr caps as opposed to general purpose for smps. The Panasonic FR series (and others) would work. Check the specs to match up the dia., height, and lead spacing of the caps you are replacing.

 

[Nigel Goodwin]

Look for low esr caps as opposed to general purpose for smps. The Panasonic FR series (and others) would work. Check the specs to match up the dia., height, and lead spacing of the caps you are replacing.

Yes, low ESR types are best, and I tend to stock Panasonic ones at work.

 

[AtomSoft]

Thanks guys! I found these:
https://www.mouser.com/ProductDetai...uxZJE0rXi6N2YiN2NnK5AxP2656kU%2b4l3PSbf9qBIg=

Almost a perfect match. (slightly shorter)

 

[duffy]

sometimes the failure of the capacitors causes further damage.

The further damage would most likely be those drivers.

it's FAR more likely they are perfectly fine.

Wait - what?


Atomsoft - the logo on those DPAK style drivers is from "Alpha & Omega Semiconductor", and like many manufacturers, they annoyingly assume you will include the letters in their stupid logo with the part number. So it's actually an "AOD408" you are looking for.

Here's a spec sheet in case you wind up having to cross it -

https://www.electro-tech-online.com/custompdfs/2012/04/AOD408.pdf

 

[Nigel Goodwin]

The further damage would most likely be those drivers.

That would be exceptionally unusual. The most common problem is corruption of the EEPROM, followed by any large IC's, and the PSU IC.

Wait - what?

There's nothing to suggest they might have failed, discolouration of the PCB is normal when used as a heatsink.

 

[duffy]

That would be exceptionally unusual. The most common problem is corruption of the EEPROM

I don't know where you're getting your information, the ones I've dealt with had internal shorts (which is why they overheated and blew the safety) and the "most common problem" I saw was blown fuses and blown drivers.

And you can add "Illinois Capacitor" to the list of shame, we had to recall and replace all of them.

 

[Nigel Goodwin]

I don't know where you're getting your information

From 41 years (and ongoing) as a TV engineer

the ones I've dealt with had internal shorts (which is why they overheated and blew the safety) and the "most common problem" I saw was blown fuses and blown drivers.

If the transistors are S/C they are obviously faulty, but the PCB been discoloured doesn't mean they are faulty - it's common.