Samsung EU40F6400 power cycling

[pvl87]

hi there,

i have an issue with my 2,5 years old Samsung UE40F6400 TV.
it's power cycling and clicking.

with the help of this forum i tried the basic troubleshooting tips and i noticed that when i disconnect the cable from PSU to mainbord the power cycle becomes faster, but the backlights don't stay on.

thought it may be the LED's and stripped the TV down and inspected the LED's, but they're all working and there is nothing obvious to see, such as burnmarks etc.

when i connected the PSU and mainbord and powered up the TV i noticed the upper 3 bars light up fine, but the lower 4 bars are dimmed.
checked the 'distributor' strip on which the LED bars are connected, but again nothing obvious.
note: inspected while still powercycling. (took picture with burst and uploaded the most clear one)

now i'm stuck a little, because i haven't seen another case similar to mine on this forum.

i'm leaning towards a bad PSU board, but want to be as sure as possible before ordering a new one...
checked the front an back of the board, but again, nothing to see.... no bulged capacitors, bad components of signs of cracked or bad solderings.

i attached a picture of the LED situation when power cycling.
also a (internet) picture of PSU board, i have exactly the same one and also included a repair manual i found an used to this point.


any help would be much appreciated!

[budm]

Re: Samsung EU40F6400 power cycling

I would first resolder the transformer legs and the legs of the devices mounted on the heatsink, specially those legs that soldered to the rivet through hole.
The backlights should come on and stay on when the cable between the main board and the power supply board is not connected.
BTW, this TV has 4 LED strings and 4 driver circuit for each string.

[pvl87]

Re: Samsung EU40F6400 power cycling

thanks for the advice!
i'll give that a go.

you're definitly aiming for the PSU board right?

maybe a stupid question, but i see 5 sets of wires (blue + black) going into the led strips, is one set for diagnostic purposes or something?

[budm]

Re: Samsung EU40F6400 power cycling

Connector CNL802 has chart for pin out to tell you what they are. The chart shows 4 pair of wires, so we need the pictures to see what are the connector. At this point you do have all 4 set of LEDs light up but two of them are not lit up properly so you need to check the Voltages on those pins.

[pvl87]

Re: Samsung EU40F6400 power cycling

correct, 4 sets on the chart on CNL802.
other pair of wires is on 15 and 16, which show as NC on the chart, don't know what they're for then....

so, reflowed TM801CS, DM857C, DM858C, DM953C, DM854C, TS801CS and LP802CS.
now, let"s see what'll happen

[pvl87]

Re: Samsung EU40F6400 power cycling

also reflowed CP806 and 807.

well, F*** me! the backlight actually stays on!
i can't believe it!

i guess i'll rebuild my TV and report back on the outcome!

thanks so far BudM!

[budm]

Re: Samsung EU40F6400 power cycling

NC = No Connection

[pvl87]

Re: Samsung EU40F6400 power cycling

don't know if it was just luck, but i refitted the screen etc, (tested the backlight once more before though) en tested again and it's back to clicking, dammit.

i'll reflow the previous connections again and try again. we'll see what happens.

some testresults from when the screen stayed on:
0 volts on all led wire pairs, don't know why exactly. can't measure with the connector on though.
the 2 big caps do 386 volts. go back to high 370's and go back up again, is this normal?

[pvl87]

Re: Samsung EU40F6400 power cycling

reflowed again, no luck.

i did some measuring and noticed that cap C9154 does about 40 Volts and his neighbour C9254 does about 80 volts. is something wrong here?

[budm]

Re: Samsung EU40F6400 power cycling

reflowed again, no luck.

i did some measuring and noticed that cap C9154 does about 40 Volts and his neighbour C9254 does about 80 volts. is something wrong here?

That means the Boosted Voltage for the C9154 is not working.
So the C9254, 9454, and 9354 all have about 80VDC?
I will have to trace out the circuit of that Power supply board BN44-00622B to see how it works.
shopjimmy does not have any pictures of the BN44-00622B so I will need the good clear pictures of the whole bottom side of the board for me to be able to trace out the circuit.

[pvl87]

Re: Samsung EU40F6400 power cycling

here is a picture of the underside.
i think the forum is compressing it though.

hope it's viewable!
there are 2 rectangular holes in the right of the picture, the mentioned caps are located there.

i'll do some more measuring this evening.

[thoma]

Re: Samsung EU40F6400 power cycling

http://televid-sib.ru/index.php?topic=27588.0

schematic Power Supply BN44-00622B Samsung!

Registration required!

regards thoma!

[budm]

Re: Samsung EU40F6400 power cycling

http://televid-sib.ru/index.php?topic=27588.0

schematic Power Supply BN44-00622B Samsung!

Registration required!

regards thoma!

Hi thoma, some how I cannot download that PDF. Can you do it and upload it here? Thanks.
I found them on the net but it does not match the board at all.
For example:
https://electro-medical.blogspot.com...ply-board.html
Many sites show the same diagram but it is not even close to what on the board.

[pvl87]

Re: Samsung EU40F6400 power cycling

i found these online.
they're barely readable though. i couldn't tell if they match or not, you guys have any idea?

[pvl87]

Re: Samsung EU40F6400 power cycling

i was thinking about switching the 2 capacitors (since they are both the same) and see what happens, but they are bonded. does that have cooling purposes? or just bonding?
i don't have that kind of stuff. the normal bonding only variant i do have.

is there a chance of succes if i switch the 2 capacitors?

[budm]

Re: Samsung EU40F6400 power cycling

i found these online.
they're barely readable though. i couldn't tell if they match or not, you guys have any idea?

I found that one too, but it does not match the board.

[pvl87]

Re: Samsung EU40F6400 power cycling

That means the Boosted Voltage for the C9154 is not working.
So the C9254, 9454, and 9354 all have about 80VDC?
I will have to trace out the circuit of that Power supply board BN44-00622B to see how it works.
shopjimmy does not have any pictures of the BN44-00622B so I will need the good clear pictures of the whole bottom side of the board for me to be able to trace out the circuit.

correct, C9254, 9454, and 9354 all have about 80VDC.
the board seems to be functioning now, with C9154 at 42VDC. maybe 40 or less means power cycling. not sure why it's showing this behaviour though.
i'm sure it will get below 40 sooner than later.
all other caps show reasonable voltages, the ones in pairs all have similar voltages compared to their neighbour. i don't think those are causing any problems.

anyone with input on my earlier question?
i was thinking about switching the 2 capacitors (since they are both the same) and see what happens, but they are bonded. does that have cooling purposes? or just bonding?
i don't have that kind of stuff. the normal bonding only variant i do have.

is there a chance of succes if i switch the 2 capacitors?

i want to rule out C9154 being the reason, but the bonding is holding me back for now.

[pvl87]

Re: Samsung EU40F6400 power cycling

http://electronics.stackexchange.com...ff-on-my-board

just non conductive bonding agent i think. i'll remove the caps and see if i can get a clue if that one cap went bad.

[pvl87]

Re: Samsung EU40F6400 power cycling

switched caps C9154 and C9254 with some weird results.
C9154 gives 80VDC on its new position (did 80VDC on its previous position)
C9254 gives 160 (!) VDC on its new position (did 40VDC on its previous position)

(did not connect the LED strips or main bord on testing runs)

i guess its that capacitor after all? how the heck did it go double in VDC though? tried to resolder the component with same results.
i'll see if i can get a new capacitor somewhere and try again!

[vinceroger69]

Re: Samsung EU40F6400 power cycling

maybe a failing capacitor and some how the heat from resoldering it is making it work/not work just replace them both with new and hopefully it will fix the issue.