Samsung 50" plasma PS50Q97 with a dead main board

[dokma]

Re: Samsung 50" plasma PS50Q97 with a dead main board

Logic board is the one connected to CN807, it connects to Y and X-Main boards, main board is the one with the audio/video inputs.

DX808 is a zenner diode that may have been damaged.

That is not a Zenner. It is a Schottky double diode rectifier. It cannot cause wrong voltage on the rail. Only the regulator can cause high voltage from the transformer to reach the 5.3V rail from what I understand (which is not much).

[dokma]

Re: Samsung 50" plasma PS50Q97 with a dead main board

So I was right after all. It was the ICX802 MC33167. I replaced it with MC34167T-MOT in the same TO-220-5 packaging (which I found to be equivalent with 0% difference according to some site). Now I have stable 5.3V at the 5.3V test point and the power supply does not click off after I jump PS_ON and plug it in.

@Biruslapio - You saved me with that schematic!

TEST PATTERNS NEXT! I HOPE.

[Biruslapio]

Re: Samsung 50" plasma PS50Q97 with a dead main board

I thought about that way later after I answered, that's obviously no Zener, duh.

But you need now a new logic board? Since both have been damaged by the PSU, the test patterns are generated by that board.

LJ92-01452A is that your board?

[dokma]

Re: Samsung 50" plasma PS50Q97 with a dead main board

I thought about that way later after I answered, that's obviously no Zener, duh.

But you need now a new logic board? Since both have been damaged by the PSU, the test patterns are generated by that board.

LJ92-01452A is that your board?

The board connected to CN807 is fried. That is the one that flamed out. LJ92-01452A is the control board from what I understand. I hope that one is not fried and that it will be able to generate the test patterns. Is there any danger in just trying to generate the test patterns with what I have right now? From what I understand, I can run the test patterns without the board connecting to CN807. I just need a jumper and a resistor if I got it right.

[Biruslapio]

Re: Samsung 50" plasma PS50Q97 with a dead main board

Control board = Logic board, CN807 goes to CN2000 which is said board, both of yours must be fried by now, the only thing you don't need for test patterns is the main board.

Don't know how to set up the test patterns for this board, tvtimmy might know, he asked for pictures of the logic board in post #6

[dokma]

Re: Samsung 50" plasma PS50Q97 with a dead main board

I found the instructions for this set somewhere on the forum a few weeks ago. I'll find them again and try to run them. I just hope the control board is not fried.

[dokma]

Re: Samsung 50" plasma PS50Q97 with a dead main board

For posterity: detailed test patterns instructions with tricks and pitfalls for this exact set: https://www.badcaps.net/forum/showthread.php?p=735168

[dokma]

Re: Samsung 50" plasma PS50Q97 with a dead main board

Nothing happens (other than the relay clicking on and staying on) when I plug everything up and jump pins 5 & 6 on the control board and PS_ON to ground on the power supply. I've identified that the compromised 5.3V rail goes to 3 boards: main board, control board and the long board along the bottom of the back side which I do not know what it is. I think I saw one blown up component on that long board across the bottom. I will try to investigate further tomorrow.

[dokma]

Re: Samsung 50" plasma PS50Q97 with a dead main board

Some hopeful news again. The control board in the TV is: LJ41-05188A. I am not too sure if that is the original one or they tried to replace it and got it blown again. My control board has a blown fuse on the 5.3V rail. Let's hope the fuse protected everything behind it.

Can anyone confirm that this control board actually belongs to this TV?

[dokma]

Re: Samsung 50" plasma PS50Q97 with a dead main board

From my google "investigation" it appears that the control board LJ41-05188A that is in my TV at the moment comes from a PS50C96HD and that the one that should be in there is LJ41-04776A. I have no idea if LJ41-05188A is compatible with this model. It looks like someone figured out the fuse was blown on the control board, slapped a similar control board in and the fuse blew again due to 19V being present on 5.3V rail.

Is there any easy way to tell if LJ41-05188A is even compatible with this model or should I just chuck it out?

[Biruslapio]

Re: Samsung 50" plasma PS50Q97 with a dead main board

LJ41-05188A is from Samsung T5054, I looked up pictures and they seem identical to your model except for the main board, it has different inputs, the only physical difference between the logic boards is:

LJ41-04776A says "50HD W2A LOGIC MAIN" 50W2A
LJ41-05188A says "50HD W2A PLUS LOGIC MAIN" 50W2A+

They should work, maybe you will have to swap the eeprom to have perfect image.

[dokma]

Re: Samsung 50" plasma PS50Q97 with a dead main board

Looks like I wrongly identified my TV as PS50Q97HD. LJ41-05188A is likely the original board from this TV and that would make my TV actually a PS50C96HD. If I'm not mistaken again. Not having the sticker at the back is a pain...

[dokma]

Re: Samsung 50" plasma PS50Q97 with a dead main board

So I tried to find the short on the control board by injecting voltage. Nothing gets warm even when I inject very large amperage, like over 3 amps at 5V. What is likely to cause this? Remember that the shorted 5.3V rail was exposed to 19V by the faulty power supply. What is the most likely to go short in this scenario in such a manner that nothing gets hot from over 3A at 5V?

[dokma]

Re: Samsung 50" plasma PS50Q97 with a dead main board

I brought the control board to a motherboard repair service. The technician says it's probably not the Zener that I was suspecting and that I should flood the board from a battery instead? I have some 18650s laying around so I will try that. My frist attempt to find the shorted component failed because the resistance of the short is super low. Something like .1Ohm. I suspect the battery will fail to get anything hot at that resistance. But the tech insisted I should try it. I still suspect that Zener at the input. I think it's a protective Zener placed there for the express purpose of shorting on overvoltage.

[Biruslapio]

Re: Samsung 50" plasma PS50Q97 with a dead main board

An ATX power supply can provide lots of current in the 5V output.

If you plug it in(5V) and the short goes away immediately it means it was some silicon, replace the board.

[dokma]

Re: Samsung 50" plasma PS50Q97 with a dead main board

Couldn't figure out what was wrong with the control board. The new one is on the way. My next concern is the Y-buffer. Any chance it survived a 19V spike on a 5.3V rail?

[Biruslapio]

Re: Samsung 50" plasma PS50Q97 with a dead main board

In the TV bottom horizontal are the adress buffer boards, E and F, If the TV does not work with the logic board replacement, might be worth inspecting those boards, if nothing is wrong, it went straight to the COFs in the panel, then it would be goodbye.

[dokma]

Re: Samsung 50" plasma PS50Q97 with a dead main board

Finally got the control board. It took so long that I also managed to get one locally, so now I have two control boards. I've plugged the control board in and tried the test patterns by jumping PS-ON and pins 5 and 6 on the control board, as per post referred to earlier. I have also tried jumping pins 3 and 4 on the control board but the result is the same - no image on the display. The control board lights up one LED immediately on power on. After a second, another LED lights up. After an additional second, a third LED starts blinking at 1 sec intervals and the second LED turns off.

I have checked voltages all over the TV, VA and VS are 63 and 207 - as per the sticker. I have found voltage on all the boards in different places and it appears as if though the TV is fully up and running but there is no image on the display. It feels like this one needs just a bit more coaxing to get it going. I just don't know where to prod next.

[dokma]

Re: Samsung 50" plasma PS50Q97 with a dead main board

Ok, new developments. I've been watching lots of videos on this particular model. This one was on the money: https://www.youtube.com/watch?v=JjQ-...eeceyburger123

This is the cap that seems to have gone on mine: https://youtu.be/JjQ--2SZdyY?t=650

I bought a cheap MG328 multifunction tester and found out that the cap from the video is 87uF instead of 680uF with an ESR value of 98 Ohms while it should have less than 0.02 Ohms or so. So my next step is to replace that cap and see where it leads me.

This one was also worth the watch: https://www.youtube.com/watch?v=DC_7...annel=TampaTec

as well as this one: https://www.youtube.com/watch?v=3Oq2MsU0XOQ

[dokma]

Re: Samsung 50" plasma PS50Q97 with a dead main board

Cap replaced. No improvement. I've discovered that my Y-Sus voltages do not match this document: https://www.badcaps.net/forum/showpo...0&postcount=40

I have 15V on almost all of the pins. At CN810 I have 206V for VS and the lowest pin on the connector has 15V. Does anyone know which voltage should be on that lowest pin on CN810? I will attach a picture of the connector.

Ok, so CN810 is:

VS: 206V
VS: 206V
GND
GND
GND
VG: 15V

Which is exactly as it should be. So power supply is OK.

Now it's down to figuring out why my voltages on the Y-Sus are wrong...

U5706 test points all read 0.5V or 0V... Here is the problem...