Samsung PN51D450A2DXZA - buzzing noise, no video.

[ngth82]

Hi all -

I picked up a Samsung PN51D450A2DXZA plasma TV yesterday. When I turn it on, i hear the relays click on and a short buzzing/screeching noise followed by the Samsung "start up sound".

Rather than hijacking other peoples threads, I'm trying to determine if this "screeching" noise is indicative of a panel failure. If it is, i'll just stop and not invest any more time on it.

The LED blinks 5 times as far as I can recall. The green LED on the small middle logic board blinks on and off. Pics attached.

I did find the "fast track" guide here: http://www.toms-service-manuals.com/...&Search=Submit

I tried following slide to "Activating Power & Logic Board Test Patterns without Main board" but i was not successful. The instructions are terse, but from what I gather:

1. Unplug the unit.
2. Use a jumper across pins 3 & 4 of the four pin header.
3. Remove the power connector from the main board (CN101 on the main).
4. Short PS_ON (pin 1) to GND (pins 3, 5, 6 or 9).

The display did not turn on.

This is the first Samsung plasma that I've debugged -- all the "extra" boards on the back of this TV will require some more acquaintance i'm sure. So some help would be most appreciated.

Thank you,
Thomas

[ozzy214]

Re: Samsung PN51D450A2DXZA - buzzing noise, no video.

Screeching noise coming out of speakers or boards? Every Samsung I ever came across was always a y buffer failure. One of the first tests I do is unplug the power cable from the psu and power on the tv. If screeching nose goes away, then the y sustain is drawing too much juice on start up and shorted.

Look at the y. You will see one connector going back to z board. Then another to psu and then the flat mylar ribbon. Unplug the one to the psu.

I see no bad caps on the boards which could be indicative of bad caps. When caps blow or ready to blow, they make a god awful screeching or whining or whistling till it is gone completely. My lcd computer monitor hooked to the security cameras just did that LOL!

[ngth82]

Re: Samsung PN51D450A2DXZA - buzzing noise, no video.

The screeching Combes from one of the boards. I disconnected the speakers to test that idea when I first powered it up.


I'll take the cover off the back and check the boards tomorrow. Thanks for the tip!

[ozzy214]

Re: Samsung PN51D450A2DXZA - buzzing noise, no video.

Whichever board is buzzing is the culprit. Shorted mosfett, bad cap. My money is on the y board. Seems to be high failure in these. Which is shrieking is where to start!

[ngth82]

Re: Samsung PN51D450A2DXZA - buzzing noise, no video.

lol.. it is really difficult to determine which board is doing the short screeching noise at start up, followed by the Samsung start up sound.

I'm using a power strip so i can remove and reapply the mains power to get the noise to repeat easily. However, i can't determine which board is actually making the noise. It sounds more like the panel itself. Is that possible?

I did manage to get a few tests in this morning. I'll try some additional checks when i get home this evening.

1. Disconnecting the LVDS cable from the logic board to the Y-drive causes the short screech to stop, but that is now replaced by a constant buzzing noise - not sure if this is a valid test or a good indicator that something with the Y-buffer or Y-drive.
   
2. I disconnected the panel LVDS flex cables from the Y-buffer (left side), and power(?) flex cables from X-drive boards (right side). The short screeching noise stopped. But since the panel is no longer hooked up, and there is no electrical load on the X and Y boards, that doesn't really tell me a whole lot.
   
3. I checked the FETs and caps on the Y-driver board - they do not appear to be shorted. They visually look good as well - no signs of damage.

I looked up a few videos online on how to check the Y-buffer for bad parts. Visually, the IC's on the Y-buffer visually appear to be intact.

Does anyone have a schematic for this TV? I found the service manual, but a schematics would greatly help.

I'll follow up this evening, but any additional help would be much appreciated.

Thank you,
Thomas

[ozzy214]

Re: Samsung PN51D450A2DXZA - buzzing noise, no video.

No not the lvds cable from the y board...the actual power cable from psu to y!

[ngth82]

Re: Samsung PN51D450A2DXZA - buzzing noise, no video.

Oh yes...
Sorry, I DID get the power cable from the main to the Y-board disconnected. That should have been on my list too.... it's too early in the morning. I haven't had my coffee yet.

#0: I disconnected the power cable from the SMPS board to the Y-board. Once disconnected, the buzzing / screeching stops entirely.

After i did this, i moved on to trying to disconnecting the flex cables from the panel to see if it was the panel or the boards.

Thank you,
Thomas

[ozzy214]

Re: Samsung PN51D450A2DXZA - buzzing noise, no video.

Then the y board is the problem. Blown mosfett, shorted cap, etc. Once you disconnect the juice from it and noise went away, that should be your problem.

I have had 5 of them in the last mnonth all blown y boards. But the buffers were amzingly good.

The y should be more than 30 bucks on ebay.

Last one I gambled and bought a untested y board, because the seller offered a return if it was nfg. So I bought it and worked flawlessly. Paid 30 think.

But your are gambling just changing the y without changing the buffer. Personally I would study the buffer carefully. If any of the ics look burnt, has pits, or craters, then its blown. If not, then your choice to roll the dice.

Its a 50/50 shot buffer may take new y out....so your choice. Maybe another member can step in to tell you how to check the buffer. As I don't know a good way to check it.

But what you can do is this. Since we are down to y. Pull the buffer from it and then plug y back into psu. If buzzing is now gone, then good chance buffer is shorted not y!

[ozzy214]

Re: Samsung PN51D450A2DXZA - buzzing noise, no video.

What is the y main board number? I may have one on the shelf I can sell you cheap that is good. Was pulled from a working tv with a broken screen!

[ngth82]

Re: Samsung PN51D450A2DXZA - buzzing noise, no video.

What is the y main board number? I may have one on the shelf I can sell you cheap that is good. Was pulled from a working tv with a broken screen!

Hey Ozzy214 -

Thanks for the last reply and the offer for the y-main board. The identifiers that i could see from the y-main board are:


MODEL NO: 50DH/DF Y-MAIN (1LAYER)
PCB NO: LJ41-09423A
REV NO: R1.3 (10/12/24)

Unfortunately, the pic that i have doesn't clearly show the PBA (circuit board assembly) number. Let me know if you have the PCB that is of the same "vintage".. i'd be willing to purchase it from you.

I ended up picking up another PN51*** Samsung with a busted screen yesterday afternoon. I haven't had a chance to open it up to see the internals. Hopefully they are a match.

-Thomas

[ozzy214]

Re: Samsung PN51D450A2DXZA - buzzing noise, no video.

Sorry my friend. I must have sold the y main board or used it. All I could find on the shelf was a x main probably for that tv.

[ngth82]

Re: Samsung PN51D450A2DXZA - buzzing noise, no video.

Sorry my friend. I must have sold the y main board or used it. All I could find on the shelf was a x main probably for that tv.

Not a problem!
I'll keep you in mind if i find that the x main board is bad

[ngth82]

Re: Samsung PN51D450A2DXZA - buzzing noise, no video.

Sorry guys, I've been away for the last week for a long Fourth of July weekend. I hope those in the US had a great fourth of July.

I've been thinking about purchasing the Y-board. I don't know how much money i really want to put into this TV as I just got my LG 55LV5500-UA running last week.

Additionally, I was in the garage today and i accidentally knocked something solid against the glass and it now has a pin point spider crack - see picture. The symtoms appear to be the same, but with the NEW crack in the glass, this is really not something I want to invest in .

Let me know your thoughts. Would this still be worthwhile?

Thanks!
-Thomas

[ozzy214]

Re: Samsung PN51D450A2DXZA - buzzing noise, no video.

Tv is done for now....

[ReeceyBurger123]

Re: Samsung PN51D450A2DXZA - buzzing noise, no video.

The Tv is trash now sorry, cant fix the glass when its cracked as you will short the panel electrodes out and the gases will also leak. Trash it

[ngth82]

Re: Samsung PN51D450A2DXZA - buzzing noise, no video.

Yeah, i figured as much. I was SO close... I'll salvage the boards and keep them for any additional PN51D450A2DXZA's that I may get down the line. I'll drop the chassis off at the local goodwill for eWaste recycling.

Thanks guys. Thread closed.

-Thomas