Samsung / Hansol BN44-00428b

[kenny1070]

Having a power supply problem on a Samsung UN55D6400UF.
This is one of those LED smart TV's (2011), with the led driver is built into the PSU.

Here's the problem:
- locked in Stand-by mode (blinking 2 red)
- Relay cycles on/off (about 5 secs.)
- No Backlight
(with CNM803 disconnected from the Main board - Forced Backlight does not turn on any of the Leds.)


I'm assuming that the Led driver (circuit) is what's causing the protection mode, and shutting down the power supply ?


All readings are at the PSU with CNM803 disconnected from Main board (forced backlight mode)

CNM803
1) 5.30
2) 0
3) 5.09
4) 0
5) 0
6) 0
7) 12.80
8) 0
9) 12.80
10) 12.80
11) 17.09
12) 4.74 *
13) 17.09
14) 0
15) 0
16) 0
17) 5.40
18) 5.40
19) 5.40
20) 3.20
21) blank
22) blank

* BL_On only generates 0.24 vdc when main board (CNM803) is connected to P/S



CNL802a
1) 62.7
2) 62.7
3) blank
4) blank
5) blank
6) blank
7) 5.90
8) 5.70
9) blank
10) blank
11) 0
12) 62.70
13) blank
14) blank
15) blank
16) blank
17) 0
18) 5.60
19) blank
20) blank
21) 1.80
22) 1.80


CNL802b
1) 124.1
2) 124.1
3) blank
4) blank
5) blank
6) blank
7) 0
8) 62.7
9) blank
10) blank
11) 124.1
12) 124.1
13) blank
14) blank
15) blank
16) blank
17) 62.7
18) 62.7


With all that being said (whew)

I'm drawn to the discrepencies in:
CNL802a 11/12 and 17/18
CNL802b 7/8

Are the Led outputs all suppose to be in tandem ?

[borifrank]

main boar error on e prom can cause power supply failure. must try to reset it.

[budm]

Please verify the connector numbers, per sch you have provided there are three connectors: CNM801 (page 2), CNL801A (page 4), and CNL801B (page 5).
I am trying to match your readings per SCH diagram to see what you should have.

[budm]

As you can see from the SCH, the LED backlights may not come on due the lack PWM (PWM_DIM1, 2, 3, and 4) from the main board. Need to look at the function of the PWM IC 9151S/9251S.
There are 4 strings of LEDs.
#1 string get the B+ feeding the Anode by D9151 (VF_CH1), the Cathode side is returned to the power supply negative through MOSFET Q9153, R9165. The MOSFET is PWM driven.
#2 string get the B+ feeding the Anode by D9251 (VF_CH2), the Cathode side is returned to the power supply negative through MOSFET Q9253, R9265. The MOSFET is PWM driven.
#3 string get the B+ feeding the Anode by D9351 (VF_CH3), the Cathode side is returned to the power supply negative through MOSFET Q9353, R9365. The MOSFET is PWM driven.
#4 string get the B+ feeding the Anode by D9451 (VF_CH4), the Cathode side is return to the power supply negative through MOSFET Q9453, R9465. The MOSFET is PWM driven.
I have not analyze the protection and error detection circuits yet. But you can at least check the DC voltage of VF_CH1~CH4.
If there is error that cause the LED to shutdown, I would expect the LEDs to come on first then the error detection will go into shutdown AFTER the LEDs flash on at least.

[kenny1070]

Sorry for the confusion on the connectors (type-o)

Just to re-verify the connectors:
CNM801 = PSU - to Main board / CN201 (20 pin)
CNL801a = led driver output (22 pin)
CNL801b = led driver output (18 pin)


Here's where I'm a little confused.
In the Training Manual no power flow chart (pg.48) it asks:
Check Backlight On - when 20 pin cable unconnected ?
No -> Change 20 pin cable / Change Main Power Ass'y

So if the "Forced Backlight On" is operated with the 20 pin cable to the Main Board (cnm801/cn201) disconnected - wouldn't the PSU be the driver for the backlight (leds) ???

If so, couldn't the problem be localized to the Power Supply unit itself ?

I'm not sure, I'm guessing.

[budm]

OK, I am glad you are able to get the training manual, so the board has the pull up resistors for the PS_ON and the BL_ON signals which are on the power supply board, the main board will keep these two signals LOW, when the TV is on, the main board will let these two signals go HIGH to turn on the PS and the BL. So from your test results, the main board is not the problem because the backlights do not come on when main board is not connected which allow the BL_ON to go HIGH, and the backlights circuit does not require the DIM PWM signals to run the backlights.
Next step will be troubleshooting the LED power supplies and the drive circuits.

[kenny1070]

Fantastic, that's the kind of good news I was hoping for.

Since this is the first one of these integrated boards that I have dealt with, it helps me to confirm that at least I am going in the right direction.

And, If I understand this correctly - I guess that explains why the 4.74v (high) on pin 12 (BL_On) of cnm801 drops to 0.24v (low) when the 20 pin cable is connected to the Main Board ?

So, since it is highly unlikely that ALL of the Leds went out at the exact same moment - I would have to assume that there was some kind of a main power (common) failure to the Led driver on the PSU - affecting all the leds ?

Does any of this sound about right ?


Thanks again
I really do appreciate all your help

[budm]

"I guess that explains why the 4.74v (high) on pin 12 (BL_On) of cnm801 drops to 0.24v (low) when the 20 pin cable is connected to the Main Board ?" Yes, the main board is keeping it down, and it will let it go high when TV is turn on.

If one of the LED string has an open or shorted circuit, the circuit will go into protection mode, but that will happen AFTER the circuit fire up the LED, that is why I ask if you did see the backlights flask on first before going dark.
Thanks for posting the manuals.
The old design has the pull-up resistors on the main board so you have to provide your own pull up to do the power supply stand alone testing, I guess the manufacturers got smarter and reading badcaps.net

[kenny1070]

Thanks for explaining it in a way that I could understand.

Now I have a much better concept of how this kind of system is suppose to work.

As far as the Backlight - I did reconfirm this in a completely dark room (nightlight included) when I first plugged in the A/C cord. No backlights at all.

I'll probably sit down tomorrow, and see if I can decifer the Led circuit.

I'll let you know what I find - if anything

Thanks again

[kenny1070]

Note:

The board that I have (PSU) is actually a BN44-00428A - not a "B".

The scheme for the A is unavailable - at least none that I can find.

I have been using this board schematic as a template, because the overall design is basically identical. Since the only real differences are in the component Id's and values, I have been simply transferring these to match the "A" board layout.

So if I make an error / type-o (or forget) in the transfer, please let me know.

Thanks

[budm]

So on my post 4, I would verify all 4 VF_ch1~4 to make sure they are present when TV is turn on.

[kenny1070]

Had a hard time trying to cyfer the Led driver output cicuit, so I decided to make my own diagram. I only went back as far as the inductors - but this is what I have, so far.

This is an overall track line / wiring diagram - traced directly on to the board itself.
Certainly provided a lot more clarity on the overall system - but also questions:

Are the Led lights (backlight strings) run in series as opposed to parallel ?
- note the correlation on the 62.7 (pin 8/12 , 18/2 , 7/11 , 17/1) - no input or output

-Or-

Are the connectors (pinouts) split top / bottom :
124.1v (2) feeds 62.7v (8) jumper to 62.7v (12) feeds 5.7v (18) etc...

Not sure - still somewhat confused.

[budm]

OK, since the diagram does not match the version of your board. You can still check the voltages, there are 4 black caps laying on the side, you can check the DC voltages right at the two legs off those caps.
http://assets.shopjimmy.com/media/ca...bn4400428a.jpg

[kenny1070]

"So on my post 4, I would verify all 4 VF_ch1~4 to make sure they are present when TV is turn on. "

Unable to do so, as the set is locked in Standby ( 2 red blinking/flashing) - no turn on operation.

Well the design matches, just not the enumeration (sch -to - board) - easy work around. (had the same on a sony kdl - and thanks by the way for that)

The trace seems to be leaning towards the string on the left / top (mid board).

I'll plug it back in and report back

[kenny1070]

Would it be OK to test this with the Led output connectors (cn801a - cn801b) disconnected / unplugged ?

[budm]

I beleive the circuit will go into shutdown if LED strings are not connected. When you first turn on I do expect the voltages on those 4 caps, unless when it first it powered up it does the self test first then report the error. I did not have a chance to look at the training manual yet to get the explanation on how the board functions.

[kenny1070]

OK, so I went back and voltage tested each of the components ( 7 per) on each of the 4 strings - All Good.

Each of these appear to be the Primary voltage supply for their led outputs.
I was also able to confirmed and verified them at their respective destination points by their 124v power source on pins 1, 2, 11, 12 of the 18 pin connector ( as seen in my attached wiring diagram ).

Just out of interest I decided to re-test each of the voltages at the led connectors - This time with the connectors unplugged:
With your concerns in mind, I used an old Analog meter (needle). Since the needle will respond a lot faster to any millisecond fluctuations than any DMM, and a better chance of spotting any voltage/spike before shut down - I thought it was a good choice .

Readings =
124v constant on all primaries (1,2,11,12 - 18 pin conn.)
1.8v on IFC 1 & 2 (pin 21,22 - 22 pin conn.)
No other voltages present - either on initial plug-in or running ???

[kenny1070]

Based on the information provided by the board, I was able to draft a basic composite of the backlight sheme (very basic).

Based on that , I can extrapolate that there is a failure in strings 7 & 8.

With the 124v power source being provided at R7+ and the lack of the 5.7volts at L7- , I guess the question would be :

" Is the 5.7v signal on pin 17 (of the 22 pin conn.) a forward ? -or- return voltage ? "

I'm guessing that the answer to that will probably determine whether this is actually a power supply problem - or- an Led issue.

[kenny1070]

Would it be possible to jumper a 5v from another location, say pin 18 or even standby from cn801 - without corrupting or damaging the whole sys. ?

That way I could verify the integrity of either the Leds (light up - forward) -or- the remainder of the circuit pathway on the board (board powers up - false positive return).

[kenny1070]

Forget Post 18, I was not even close (design or draft).


I took it apart (panel) - and what I found was:

This system uses 2 side panel led light bars - Left/Right
CN801a (18 pin) operates the right side and CN801b (22 pin) the left.
Each connector is then split again - top/bottom (odd/even), each responsible for their own respective halves of the light bar.

The two bars are then connected by looping the right side (primary) back through the PSU to power up the left side - cn801b 1,2 to cn801a 17,18
The 5.7v is a return signal - (after voltage drop from the 124v across the Leds)

Because of this, I am fairly convinced that this is not a power supply problem - but rather a bad Led (light bar) issue.


Sorry I posted this the wrong location -
thought for sure that this was definitely going to be a Power Supply problem



I know it was a long work through - and I appreciate all your help

Thanks