samsung PS50A456

[flocko]

Hi Ysus LJ92-01516A fault have changed four shorted RJH3047s and one STW20NK50Z on board when refitted get bright white screen and then as photo? will do test pattern on logic board see how that looks

[tom66]

Re: samsung PS50A456

Do you have a scope to check the Y-main outputs? I'd check the -Vscan and Vsch voltages on Y-main, and the Ve on the X-main.

[flocko]

Re: samsung PS50A456

Thanks Tom went to check voltages and got the Ve at 93-94v then the supply to the house tripped? WTF, the two 18n50 on the power board Vs drivers have gone short so looks like the Ysus was trying to pull down the national grid network,no spare 18n50 so will have to wait but will have to look at the Ysus again maybe see if i can find one thats not too expensive.i thought it was going to well Flocko

[tom66]

Re: samsung PS50A456

Those transistors can fail if the TV gets stuck in a high-bright mode for too long, this is because it is pulling too much power from Vsus.

[flocko]

Re: samsung PS50A456

Thats what i thought pulling way to much and as i said it had bright white screen when just turned on, when i got the set in i was told it was just clicking, but you could smell burning and one of the STW20NK50Z had a pin hole burn mark on it and read dead short,the four RJH3047s were also showing dead short, the board also showed dead short on Vs to ground ,but after the parts were replaced the Vs short to ground had gone and the buffers tested good, will just have to look again but getting a little lost, i am now thinking i need to look closer at the Vscan components and lower buffers? flocko

[tom66]

Re: samsung PS50A456

Think the buffers are OK because there is a partial image. You can see the signal info dialog in the top corner of the screen..

You just need to figure out overdiffusion problem, for testing you can run Vs at minimum voltage, picture will have a pink tint or pixels not firing but will be OK for a quick test.

The vertical bar is a little worrying, could be a sign of a bad plasma panel, hope not! (Bad panels are extremely common on these models. Lines stuck on screen etc.)

[flocko]

Re: samsung PS50A456

yes the bar is a worry but it is dead mid screen so would have to be on two tabs and i dont think it that wide? Well just had a look and found a board for £29.00 inc post so thats on its way, if it works i can go side by side with the boards and meter and hopefully find the fault and then have a spare Flocko

[tom66]

Re: samsung PS50A456

That width is about right for bar fault on these panels;
https://www.badcaps.net/forum/showth...light=pn50a450

Good luck, let us know how it goes...

[flocko]

Re: samsung PS50A456

Just to update, the power board that went out had blown the SCK20206 (themistor), bridge rectifier,diode (S20LC60) and two 18N20, but is now working,the replacement YSus was used to fault find the bad one and i found the new W20NK50Z i fitted was faulty and did not appear to have its built in zener diode working, with a new W20NK50Z fitted that is now also working,i still have a black solid bar on the screen,i am hoping this will be a loose connecter bar on the lower buffer fingers crossed, but i need a hand to move the set and lay it down,so it will have to wait till the weekend when my boy`s come round to give me a hand, i am getting to old for all this Flocko

[tom66]

Re: samsung PS50A456

If the bar is completely blank (no image at all) you may be lucky. If it has a line, or lines in it, the panel is probably bad. Make sure Va is discharged (<10V) before fiddling with the connectors.

[flocko]

Re: samsung PS50A456

Hi Tom that was my thinking also, yes no lines no colour at all just a black bar, there was no mention of the bar when the set was bought to me ,just that it stopped working and the relays were clicking, i hate working on these 50" and bigger sets, the one before last i was fixing a power board fault and cracked the panel trying to move it "oops" try explaining that? Flocko

[matyka]

Re: samsung PS50A456

Hello,
I have the same tv,just changed X-main LJ92-01515A ,tv starts up has sound but no backlight no picture.Readings on X-main are fine .
I tried to patern test it but still no backlight or any picture.
What would be the next step please.
Thx

[matyka]

Re: samsung PS50A456

I now notice the fuse on y-sus Lj92-01516A fuse F5800 is keep blowing and for a sec I could see the screen light up.
Any advice is much appreciated .
Thx

[flocko]

Re: samsung PS50A456

remove the board and replace the fuse , check VS+VA to ground on the main connector, if shorted check all the components on the three H/sinks for shorts. also you will find two big green resistors side by side in front of the H/sinks test for low ohms end to end on one of these ,if readings are in low ohms you have buffer ICs at fault. and I would only go on from there if you have the kit and no how to replace these, if not then look for a replacement board. Flocko

[matyka]

Re: samsung PS50A456

Checked VS+VA to ground on the main connector and has no shorts
All the components on the three H/sinks are ok no shorts
I have a short on the main connector VCC to ground is that ok ?
I took some reading on the two big green resistors side by side in front of the H/sinks are this 2 from the photos ?

[flocko]

Re: samsung PS50A456

No the ones side by side R5999/R6000 and R6001/R6002. there should be no short to ground on VCC this is I think is also an indicator of buffer IC damage

[matyka]

Re: samsung PS50A456

R5999/R6000 has 5.270-kohm one way and if I reverse polarity 11.84-kohm
R6001/R6002 has 5.281-kohm one way and if I reverse polarity 11.88-kohm

[flocko]

Re: samsung PS50A456

I test on the 200 ohm scale if you read OL or whatever your meter reads with the leads apart then that's fine (you are trying to look for low ohms short) any thing in the 200ohm scale I read as shorted on this type of thing,with the short on VCC you will need to do more testing start with the components on the heat sinks

[flocko]

Re: samsung PS50A456

Just looked at my notes for this board common faults Q5500 (20NK50 zener protected MOSFET) Q5200/Q5202 (RJH3047 IGBTs) and U5003 (ADUM1410 digital isolator) when this fails it can take out buffer ICs ,and C5997 . I hope this is of help Flocko

[matyka]

Re: samsung PS50A456

Thank you flocko very much for your notes but I decided to buy a board from ebay because found one cheaper than to buy all this parts and replace them .
The board LJ92-01516A fixed the tv .