Samsung PN51D6900

[Diva]

Hi guys,
My Samsung Plasma TV PN51D6900 went to the power cycle mode. Not a rare occasion. It is 7 years old and the picture quality was still awesome, so I decided to try and repair it if I can. I did some research online and most problems like that were described by being caused by bad capacitors.

I need help identifying what is the problem with my TV, so first here are some numbers:
TV model number : PN51D6900
Power supply board number: BN44-00446A (PSPF371501A)

And some pictures:





Symptoms:
Upon plugging on the TV powers on. In about 17-18 seconds it turns off. In another 2-3 seconds it turns off. And the cycle repeats. The longest I left it to repeat was for about 15 minutes.
While the TV is powering on the red stand by LED on the front blinks 5 times about 1 blink per second.
The green LED on the small board below the power board blinks at 1 blink per second for the whole time the TV is on.

Steps I have taken so far:
1. Looked closely to see if I can spot any capacitors that are leaking, bulged or deformed as described in this post

2. Red the troubleshooting in the service manual, but could not find a solution.

3. Measured the VS-ADJ (top right corner near the 2 caps), VA-ADJ (middle right side) and all pins on connector CN801 (bottom right corner) that supply the main board. All values are as stated in the output table below the 4 big capacitors in the bottom left side of the board or near the CN801 connector.

4. Measured all large electrolyte capacitors with a multi-meter. All values measured match the value printed on the capacitor. Some capacitors are connected in parallel and then the measured value is very close to the sum of the values of the individual capacitors (the four long caps between the heat sinks on the power board, the 2 long caps above the other heat sink on the power board, the group in the top side of the board in the left hand side).

I noticed some deviations of the measured value and the expected value tor the 2 groups of four green capacitor on the top side of the right hand side board and in the bottom part of the left hand side board. Both groups are made of 4 caps 150 micro F each, but when measured my multi-meter reads 1500 micro F for the whole group. I thought that my be the problem until the second group made by the same caps measured the exact same value.
The second deviation was the group of two brown caps 220 micro F each located directly bellow the group of four green caps on the right hand side board. their measured value was 680 micro F.

All measurements were made without removing the capacitors from the bords.

5. Disconnected connector CN804 in the top right side of the board.
The TV still goes through a power cycle, but a bit different at this time:
TV powers on for about 25-26 seconds and off for about 2-3 second and repeats.
- the red stand by LED on the front still give 5 blinks at about 1 blink per second
- the green LED gives one short blink, then stays on for 5 seconds, off for 2 seconds and repeats until the TV turns off.

6. Disconnected connector CN802 in the bottom right corner of the board (just below the heat sink) that supplies power to the small logic board.
The TV goes through another power cycle - on for about 45 seconds, off for 2-3 seconds and repeat.
- the red stand by LED on the front still give 5 blinks at about 1 blink per second
- as the logic board is disconnected the green LED is off.

7. Disconnected connector CN801 (bottom right corner) that supply the main board - TV is off and will not power on.

I appreciate any advise that can help me diagnose further and repair this TV.
Thanks

[Dcole73]

Re: Samsung PN51D6900

Hello.
First, check the voltage outputs on the power board. If any is lower than specified, it could mean it is being overloaded and this should be a start point.

While trying to repair a colleague's LG TV, I browsed through a lot of info online, one of which may help you.

Model/s: Samsung
LN46A550P3FXZA,LN46A650A1FXZA,LN46A530P1FXZA,LN46A 750R1F
XZA,LN46A860S2FXZA,LN46A950D1FXZA,
LN46A540P2FXZA,LN46A850S1FXZA,LN46A630M1FXZA,LN46A 580P6F
XZA,LN52A530P1FXZA,LN52A750R1FXZA,
LN52A650A1FXZA,LN52A550P3FXZA,LN52A630M1FXZA,LN52A 860S2F
XZA,LN52A850S1FXZA,LN52A540P2FXZA,
LN40A530P1FXZA,LN40A450C1DXZA,LN40A330J1DXZA,LN40A 550P3F
XZA,LN40A650A1FXZA,LN40A630M1FXZA,
LN40A540P2FXZA LCD TV
Symptom: Unit cycles on/off during start-up.
Repair/Solution:
If the unit tries to turn on but begins to cycle on and off before any video is
displayed and all of the SMPS voltages are good, disconnect the LVDS cable at
the T-Con board. If the set starts and the backlights come on, replace the T-Con
board. If the set does not start, disconnect the LVDS cable at the main board. If
the set starts, replace the LVDS cable. If the set still does not start-up, replace
the main board.

[tvtimmy]

Re: Samsung PN51D6900

Diva is working on a plasma tv, not an lcd.

[Dcole73]

Re: Samsung PN51D6900

Oh oh.
My bad...

[Diva]

Re: Samsung PN51D6900

So today I did some more reading and testing.
The Vscan on the Y main board is present and exactly as on the sticker. Same goes for the Ve on the X board.



I disconnected the main board from the power board and placed a jumper between ps_on and ground. The TV now powers ON and stays on, no cycling. The red LED on the front is off as it is powered from the main board.
The green LED on the logic board is flashing 1 per second.

Is this a good indication that the problem is with the main board and if so any ideas for repair, or it is a replace only solution.

[dick_barton]

Re: Samsung PN51D6900

If you think the problem is on the mainboard then can you run the test pattern. With the power off place a jumper on the Logic Board and disconnect the ribbon cable between the mainboard and Logic Board. Power up and see if it cycles through the test patterns.

I don't know which pins you short out on the Logic Board so perhaps you could post a photo of it and give the part number.

[Diva]

Re: Samsung PN51D6900

I ran the test patterns yesterday. They all looks OK.
I had to shorten the top two pins.



What would be my next step?

[tvtimmy]

Re: Samsung PN51D6900

Find a mainboard.

[Corranga]

Re: Samsung PN51D6900

I have exactly the same issue, discovered on the same day oddly enough!

My TV is a PS51D6900 - the S representing Europe rather than the N for (North?) America in the OPs.

There seems to be a whole lot of variation in the actual number on the main board (BN94....) is there a way to tell which ones are likely to work or not, or is it just a case of finding one that has exactly the same number?
Mine is a BN94-04402Q but I can't find one for sale.

I have found a BN94-04402E, which is from another model of Samsung TV (a D8000, so same era, 1 model further up the range), but can't find any reference to how exact the number has to be / if the letter at the end is a minor revision etc...

[Diva]

Re: Samsung PN51D6900

Finding that board seems to be very hard. I searched today and it is either sold out or offering only a repair service.
I emailed Samsung Canada Parts and they confirmed that my board BN94-04402L is discontinued and offered this reply:

"Hello,


Here is the available substitute for that part. We do not have stock however it is available from the manufacturer:


BN94-04689B $321.90

ASSY PCB MISC-MAIN;PN59D700"

I'm not sure if I want to invest close to $400 (after shipping and taxes).
I'll keep looking.

[Diva]

Re: Samsung PN51D6900

Does anyone know if BN94-04402V will be compatible to replace BN94-04402L?

[Corranga]

Re: Samsung PN51D6900

I have exactly the same issue, discovered on the same day oddly enough!

My TV is a PS51D6900 - the S representing Europe rather than the N for (North?) America in the OPs.

There seems to be a whole lot of variation in the actual number on the main board (BN94....) is there a way to tell which ones are likely to work or not, or is it just a case of finding one that has exactly the same number?
Mine is a BN94-04402Q but I can't find one for sale.

I have found a BN94-04402E, which is from another model of Samsung TV (a D8000, so same era, 1 model further up the range), but can't find any reference to how exact the number has to be / if the letter at the end is a minor revision etc...

Just to update on this, I have now replace my main board:
BN94-04402Q
with a:
BN94-04709S
and the TV works perfectly.

I simply asked the eBay seller who confirmed it would work.

Also:
You posted that Samsung Canada stated that your BN94-04402L used in the PN51D6900 has a substitution part BN94-04689B.
There is an eBay seller in the US who repairs BN94-04689C boards, from the PN51D7000 (and PN59D7000).
From what I remember when researching our TV 6/7 years back, ours is essentially the same as the Samsung 7 series, but with 1 feature missing (I can't remember which, but initially thought it was maybe satellite tuner vs. antenna tuner?)
Anyway, he fixes main boards which have the power cycling issue by replacing the NAND chip which holds the firmware. I believe it has to be a pre-written chip.

I asked if he thought this repair would fix my board, on the basis that my board - he thought it most probably would, though the tuner might no longer function due to mine being a European model.

So... I'd say, first, ask the seller of the BN94-04402V if they think it'll work. I suspect it probably will with such a close number.
If you're not sure, look for the seller on eBay who repairs the boards and ask their opinion, and take it from there.

Chris

[Diva]

Re: Samsung PN51D6900

So here is my update too.
I confirmed with Samsung that BN94-04402L can be substituted with BN94-04689B and BN94-04689A. I found BN94-04689A and replaced it.
The TV worked beautifully for about 2 hours.
The next morning it went to the vicious power cycle again.

I'a at a loss as what to do next

[ajshoe]

Re: Samsung PN51D6900

I would send in your original main bd to get repaired (nicks tv) or similar that warrants there repair. I've used Nicks before. google the main board repair

[tvtimmy]

Re: Samsung PN51D6900

Try and return the main that you bought.

[Diva]

Re: Samsung PN51D6900

The guy I bought it from warned me that because it is not the original board for my TV he wont take it back.
I think the board may have had an issue that he did not suspect. He told me that he took it off from a TV with a cracked screen and verified that the board was OK. Based on that I took it.

The board works OK when you first power up the TV and all functionality is there. Even the 3D works.
The problem starts if I power down the TV and then try to power it up again.

If I let it cool down for 30-40 minutes I can power it up and watch without a problem for now. Today I was off and power the TV on in the morning and tuned it up to the Olympics. It worked for most of the day. Kids watched Netflix (so Smart Hub adn apps work too).