PN50B450 - Turns on, Sound good, I think Backlight is good, No Picture

[brnrubbr]

Model: Samsung PN50B450

TV literally just popped and picture stopped working. Sound was good.

On TV Turn on and Turn off, there is colored static that flickers on for a split second.

As odd as it sounds, I am unsure about the Backlighting. I don't see a significant Backlight after the initial Flicker. ADDITIONALLY, I do not see a picture when I shine a light on the screen.

No obvious Caps are blown. No fuses seem to be blown.

I tried the VS_On --> +5VDC, PS_On --> Ground, LVDS disconnected, Main Board Disconnected and I did not get any test patterns on the screen.

Harumph
Thoughts, ideas?

[R_J]

Re: PN50B450 - Turns on, Sound good, I think Backlight is good, No Picture

To start with the tv is a plasma so no backlight, Check and see if you have Vs voltage on the Y-sus board, I suspect either y-sus or Z-sus board problems, likely shorted fet's
Post some pictures of the rear of the tv so we can see what boards are in this set.

[brnrubbr]

Re: PN50B450 - Turns on, Sound good, I think Backlight is good, No Picture

204VDC to X-Main and Y-Main boards.

Pictures in a quick second......

[brnrubbr]

Re: PN50B450 - Turns on, Sound good, I think Backlight is good, No Picture

Picture as requested

[R_J]

Re: PN50B450 - Turns on, Sound good, I think Backlight is good, No Picture

I would inspect the buffer ic's on the y-main, look for a crack or hole in the top of the ic, then check the transistors on that board that are mounted to the heatsinks, shopjimmy lists a repair kit for the board if it is LJ92-01601A ,
Something went pop and is likely either an ic or transistor

[brnrubbr]

Re: PN50B450 - Turns on, Sound good, I think Backlight is good, No Picture

All the transistors and caps looked good, but I don't think I looked too closely at the buffer boards. That would be great if the buffer boards were the issue. i should be able to have an answer tonight

[R_J]

Re: PN50B450 - Turns on, Sound good, I think Backlight is good, No Picture

If I had a dollar for every part that looked good but tested bad... The buffer ic's are part of the y board are they not?

[brnrubbr]

Re: PN50B450 - Turns on, Sound good, I think Backlight is good, No Picture

Oops, yeah, you're right. Buffer ICs are part of the Y-Main board.

Quick findings...-ish on the X-Main...
- Faint smell of Magic Smoke near RJH3044's
- Some RJH3044's had their soldered leads covered by a cushion/pad. After I removed the pad, it looked like Samsung used dis-similar solders. It looks like a cold solder joint with dendrites coming off of it.

Y-Main
- Solder masks looks good on the ICs.

[brnrubbr]

Re: PN50B450 - Turns on, Sound good, I think Backlight is good, No Picture

Moar updates.....

X-Main
- "Cold" solder joint picture included
- No obvious burn marks, cracks, or heat-spots on PCB

Y-Main
- It looks and smells clean.
- No obvious burn marks, cracks, or heat-spots on PCB

[R_J]

Re: PN50B450 - Turns on, Sound good, I think Backlight is good, No Picture

It could be that the X-main is bad, In some cases you will get a slight picture but very dark and snowy. this would also explain the slight flickerof the screen. Check the fets with a meter.
Shopjimmy has a repair kit for the BN96-09736A, so check these parts

[brnrubbr]

Re: PN50B450 - Turns on, Sound good, I think Backlight is good, No Picture

Kit is on order. Thank you so much!! I'll try and update when everything is repaired and resoldered. Thanks again!

[brnrubbr]

Re: PN50B450 - Turns on, Sound good, I think Backlight is good, No Picture

Well...... shucks. All 4 FETs replaced and TV still isn't working. The suspected FET did smell a little smokey, but the TV still isn't working.

I'll take a closer look at the Y-Main and see if any of the buffers may have popped.

[brnrubbr]

Re: PN50B450 - Turns on, Sound good, I think Backlight is good, No Picture

No obvious popping nor venting of any component. If anyone knows where I can get a troubleshooting manual for the TV, it would be a huge help.

I'll verify everything on the manual below.....

[brnrubbr]

Re: PN50B450 - Turns on, Sound good, I think Backlight is good, No Picture

X-Main
VCC = 15.1VDC
Vss = 209

Y-Main
Va = 54.7VDC
Vc = 15.1VDC
VS = 209VDC

Logic Board
D5.3 = 5.2VDC

Again, to recap.... the screen flickers snow on startup and shutdown. Sound is good, display is not during normal operations. Any additional thoughts regarding troubleshooting would be a huge help.

[brnrubbr]

Re: PN50B450 - Turns on, Sound good, I think Backlight is good, No Picture

Per.....
https://www.youtube.com/watch?v=sNZVkuh2Ajk

I've verified none of the Y-Main Buffer ICs are dead-shorted


Hooking everything back up on the Y-Main, applied power, and used a IR Thermometer......
- Found bottom-most Buffer U5407 @ 115 degrees F. Hot, but not hateful

- All other Buffers were room temp (i.e. not being powered)

- ***Found the middle set of FETs (903188, STTH40P03S, STTH40P03S, IRFP4332) VERY hot. I read 190 degrees F on the IRFP4332. *** Mind you, these FETs have a huge heatsink attached.


EDIT: Y-Main Repair Kit on Order --> https://www.ebay.com/itm/263925422513

[tom66]

Re: PN50B450 - Turns on, Sound good, I think Backlight is good, No Picture

Does the LED blink on your control board at a rate of about once a second?

You say you have backlight, while plasma TVs do not have a backlight they do have a minimum discharge level, so can you see a small amount of light from the screen in a dark room?

[brnrubbr]

Re: PN50B450 - Turns on, Sound good, I think Backlight is good, No Picture

Does the LED blink on your control board at a rate of about once a second?
Yes

You say you have backlight, while plasma TVs do not have a backlight they do have a minimum discharge level, so can you see a small amount of light from the screen in a dark room?
I'll edit the Backlight comment. Yes, I see a small amount of light on the screen in a dark room

Edit: Can't edit previous posts :-(

[tom66]

Re: PN50B450 - Turns on, Sound good, I think Backlight is good, No Picture

ok, show me a pic of your control board, I think I know what is going on here.

[brnrubbr]

Re: PN50B450 - Turns on, Sound good, I think Backlight is good, No Picture

Here go!

[tom66]

Re: PN50B450 - Turns on, Sound good, I think Backlight is good, No Picture

OK, 1st pic, bottom left 4 pin terminal block just near the connector with the grey wires.
Jumper pins 3 and 4 using a hard disk option jumper, alligator clip or bent paperclip or whatever works.
Disconnect the cable in the middle with the blue tab
Power on the TV. Do you see test patterns?
If so, replace the main board, the one with HDMI ports, in 2nd picture.