On/Off-cycling of Samsung-Plasma-Mainboard(BN94-03354G) repairable?

[amoll]

Hello everybody,

I have a Samsung-Plasma-TV(PS42C430A1W) which doesn't turn on and a relay on the powerboard is clicking on/off endlessly.
I removed the mainboard(BN94-03354G) and connected the test-switch(pin 3 and 4) with jumper on the t-con-board and the tv turned on and showed images.
So I think I do have a defective mainboard.
Before I order a new board, I want to ask if somebody has an idea which component on the mainboard could be damaged? Where can I spot for errors??? I have no clue...

In another thread about a different samsung-tv-model with same error pattern. I read, that on that TV a capacitor(C102) is the cause for power-cycling. Sadly on my model I don't have this capacitor?!

I would really appreciate if anybody has an idea where and what makes sense to measure to find the defect...

thanks!

[petehall347]

Re: On/Off-cycling of Samsung-Plasma-Mainboard(BN94-03354G) repairable?

not sure how those work but i just fixed a samsung lcd tv with same symtoms and it was the eeprom corrupted . i reset it and now its fine . sometimes the eeprom needs changing .
the problem started with bad capacitors on the power board so needed changing first .
not saying it will fix yours .

[dick_barton]

Re: On/Off-cycling of Samsung-Plasma-Mainboard(BN94-03354G) repairable?

Normally when you disconnect the mainboard from the control board and jumper the test point 3 & 4 and the test patterns are displayed without any issues that normally points to a defective mainboard

[amoll]

Re: On/Off-cycling of Samsung-Plasma-Mainboard(BN94-03354G) repairable?

Did some further investigations and it seems that I have a short somewhere.

Perhaps one or both of the SMDs-Caps may have gone bad or the voltage regulator(s)???

The chip on top is a buck-regulator(AOZ1021) and the output voltage pin to ground measures only 14.5 ohms.
The diode next to it measures in diode mode 2.9v in reverse. In the other direction it seems to be correct.

Seems all a bit strange to me, but I don't know if all of these are gone bad or only one component.

Any hints?
Thanks!

[amoll]

Re: On/Off-cycling of Samsung-Plasma-Mainboard(BN94-03354G) repairable?

There is another buck converter AOZ1031AI on the board where pin 1(PGND) and pin 8(LX) measures 0.3 ohms...

Any idea which components most likely short out on these boards?
Visually everything looks fine...

[dick_barton]

Re: On/Off-cycling of Samsung-Plasma-Mainboard(BN94-03354G) repairable?

Can you lift the capacitors and see if the short goes?

[amoll]

Re: On/Off-cycling of Samsung-Plasma-Mainboard(BN94-03354G) repairable?

I pretty removed everything from the top side and the short didn't go away. Then I flipped the board and removed roughly pretty much on the bottom. Finally short away...and board away!
I have to buy a new one and finally still don't know what went wrong.
If anybody has same problem in the future, perhaps better focus on the back side...
Sorry for not being wiser now and thank you for your help!

[heavymachines]

Re: On/Off-cycling of Samsung-Plasma-Mainboard(BN94-03354G) repairable?

Yikes... Not quite enough heat removing the bga chips, looks like damaged pads.

[vinceroger69]

Re: On/Off-cycling of Samsung-Plasma-Mainboard(BN94-03354G) repairable?

maybe if you could of found what line was short you could of injected voltage with a low amps and seen what gets hot etc it usually shows shorted smd parts etc

[amoll]

Re: On/Off-cycling of Samsung-Plasma-Mainboard(BN94-03354G) repairable?

Yikes... Not quite enough heat removing the bga chips, looks like damaged pads.

Yes, I know, I was impatient and the board was trash anyway...and I hardly desolder bga-chips usually...actually, I think it was my first...

maybe if you could of found what line was short you could of injected voltage with a low amps and seen what gets hot etc it usually shows shorted smd parts etc

Oh yes, that sounds like a very good idea!!! I keep that in mind for another time. Thank you for the hint!