Samsung / Hansol BN44-00428b

[R_J]

Re: Samsung / Hansol BN44-00428b

Hopefully, this is form is still active. I have had issues with my un55 powering on, the power light just blinked and would not come turn on. So here I am trying to replace the power supply board but none are available atm. Upon inspection of the board BN44-00428B I saw the contacts to the transformer are burned!

I could resolder the contacts which would possibly fix the issue but I really want to replace the transformer. Unfortunately, I cannot seem to find a data sheet to find one similar to replace. All I've been able to find is that its a EFD5055S(450uH).

Hopefully, one of yall might have some input.

The transformer will be ok, all you need to do is clean up the connections and resolder them.

[bob bimon]

Re: Samsung / Hansol BN44-00428b

Hello
I just finished to repair a Samsung TV UE45D6500 with the permanent boot cycling issue.
The root cause neither the PS board nor the processor board, but the connections between the PS board and the led bars.
One of the 2 flat harnesses supplying high volatges to led bards was flattened crushed between the power radiators and the back cover, and the isolating plastic sleeve melted and wires were touching each other between to leds strings power lines.
I repaired it, and the TV worked fine again without power cycling, except that the lower quarter part of the backlight was dead.
Checking each string voltage I noticed that a pair of strings between the total of 2x4 = 8 strings was in open circuit situation (>120V instead of 90V).
I decided to dismount the led bars.
The following video helped me a lot to dismantle the LCD screen without damage :
https://www.youtube.com/watch?v=O6KhWYSgA9c

I checked each led individually, all work fine; at the very end I discovered a opne continuity on a copper line on the bar, between the connector and the lower quarter string of one led bar.
There was a dark spot on this copper line, I scratched the paint and confirmed an open path; in fact the copper line acted as a fuse and burnt, opening the circuit.
I decided not to reuse it, event if a could just resoldering the coppler line, but I considered that some leds may have been strssed, and purchased new led bars.
I mounted them in the screen and rebuilt it, and backlight worked fine; reassembled the complete TV set and tested it, success !!

[freekey]

Re: Samsung / Hansol BN44-00428b

This thread is epic. Not sure whether I should create a new thread or update this one, but let me know if I am breaking board etiquette by replying here and I'll create a new thread.

I am troubleshooting a TV (a Samsung UN55D6420UF) that has one of these Hansol BN44-00428b boards right now. The symptoms don't look exactly like anything I could find in this forum and now I'm super curious to figure it out. I am obviously not an EE or anything but I am really intrigued by circuits.

Here is the behavior:

1. When perfectly cold and with all capacitors discharged, the TV starts right up, and will do so a few times in a row.
2. After it's been powered on for a while, if you turn the TV off and on again, it will relay-click a bunch of times before it starts up. It seems like the longer the TV has been running, the more times it'll click before it eventually comes on.
3. If it's been running for an hour or more, if you turn it off and on again, it will bootloop...you can see the logo come on for a moment and then it immediately reboots. I've let it do this for several minutes and it never fully boots, so I just unplug it at that point and let it cool down.
4. Occasionally (after 20-30 minutes or more), while watching the TV, the screen will go dark, the relays will click, and then it'll come back on. This sometimes results in an endless logo-flashing boot loop, especially if the TV has been on too long.

I put a meter on various power rails on the cold side as well as all of the pins on the main board connector. The standby voltage is around 5.5 VDC whether the TV is off or on. When the TV is successfully running, the voltage is 5.4 VDC on the 5V rail, 12.8-13.0 VDC on the 13V rail, and 17.9-18.1 VDC on the 18V rail.

However, when the relay is clicking on and off and the TV isn't booting yet, the voltage on each non-standby rail (5V, 13V, 18V) will spike up to about 25-75% of proper voltage right after each on-click, then go back down to zero immediately, and after that, the relay will click off and try again. This occurs until the "successful" on-click where the voltage gets up to where it's supposed to be.

Unplugging the main board from the power supply, there is a delay of between 5 and 20 seconds before the backlights will come on. Once they're on, they stay on, with no flickering. During the delay before the backlights come on, there is a faint crackling noise coming from the area near where the AC cable is plugged in, somewhere around the two inductor coils there. Sometimes, during the crackling noises and before the LEDs fully come up, the LEDs will flicker on each crackle. Because of this possibly abnormal behavior even with the mainboard unplugged, I'm suspecting either the power board or the LEDs (or the connections between).

I ran these tests in the dark and I see no arcing on either side of the board either during the relay-clicking power on or during TV operation.

All caps look visibly fine to me (although I know this doesn't mean they're good). I saw some questionable-looking solder pads around the large transformer, so I fluxed and resoldered every larger pad on the hot side of the board as well as every pad on the transformers, but this didn't change the behavior. I tested each diode on the board with a multimeter's diode mode and I believe they all tested good, although I may have missed one or messed this up.

I turned down the brightness and looked for bad LEDs with the TV on, but didn't find any.

I measure 440 VDC across the two 450V caps (on the right side of the board) while it's running. While it's relay-clicking at start and there's unstable power to the low voltage rails, these caps measure 440 VDC after the on-click, and then slowly discharge after the on-click.

Also measured 184 VDC on the caps that drive the LEDs on the upper right of the board while the TV is working and the LEDs are on.

The next thing I can think to do is to try and measure each IC with the board on, and compare the measurements to what the datasheet says. It's tricky to perform this kind of test because the TV mostly works... if it were bootlooping or something constantly it'd be a lot easier to measure voltages! As it is right now, I'm plugging it in and unplugging it for each test. Now I really want to buy some of those multimeter leads with alligator clips on the end...

I am attaching photos of the board in case they provide any clues. I left the flux around the solder pads so you can see which ones I resoldered. If you're as intrigued as I am by this situation and want to help, let me know if you need any other photos and/or measurements.

[bundlestars]

Re: Samsung / Hansol BN44-00428b




Thanks, I did as you described, I soldered the single leg side of the diode to the ground, the rlay switching problem was solved and the TV turned on.

If I understand correctly, you soldered this point to the ground and thereby disabled the said protection. May I ask you where the nearest ground was that you soldered to?

[bundlestars]

After I soldered this point to the nearest ground, the TV actually turned on, but it also showed me why this switching problem existed in the first place.



Can someone tell me if this is an LED strip issue or a motherboard/flex cable issue?

[bundlestars]

I fixed the problem by removing the flex cable from the T-Con board and cleaning the contacts with an air spray.

It seems that dust particles caused this, and since vertical lines usually have something to do with this particular board, I tried my luck at cleaning it again, and it worked.