Samsung LN46b530p7f – relay clicks and backlight cycling, sound OK

[momaka]

I got this TV a little over a year ago from a coworker from my previous job. It’s a Samsung 46” TV, model number LN46b530p7f.

Problem:
Backlight cycles On and Off.
Basically, when the TV is turned On, there is a relay click heard from the TV PS board. The relay cycles On and Off 4 times in about 2-3 second intervals. Each of those 4 times, the backlights also cycle On and Off with the relay. The screen TFT isn’t cracked/damaged and appears to work - I can see a “no signal” image when the backlights turn On briefly – though the image is a bit dull/dark. The greeting / turn Off chime works fine too, so the set has working sound. Also, when the backlights turn On, there is a faint buzzing heard from the inverter. I don’t know if it’s normal sound or not (I’ve seen some very noisy inverters before). But just noting it here anyways,

So is anyone familiar with this issue by any chance and what I might be the problem?

In terms of troubleshooting, the first thing I did is re-recap the power supply. Long story short, it was recapped by my colleague, but he did a little bit of a messy job and not with the most appropriate caps (Nichicon VZ general purpose caps and some Chang/Chong/X for the smaller caps). Picture of his “handiwork” attached below for comic relief.
https://www.badcaps.net/forum/attach...1&d=1547788861
https://www.badcaps.net/forum/attach...1&d=1547788861
https://www.badcaps.net/forum/attach...1&d=1547788861
https://www.badcaps.net/forum/attach...1&d=1547788861
https://www.badcaps.net/forum/attach...1&d=1547788861
Of course, all of the above “handiwork” is fixed now.

When I asked him about the original caps, he said he’s doesn’t remember if they looked bad or not. But he said that even after the recap job, the TV appeared to do the same thing as when he found it. So it’s quite possible the caps were not the issue in the first place. Nevertheless, I did a slightly better (but still temporary) recap job with a few low ESR caps mixed in with the GP Nichicons he had on there (which I checked were good, BTW.)

After this, I checked some of the power supply voltages on the main connector (the one between the PSU board and logic/video board) and connector CN1806 on the PSU, which goes to the inverter driver / balancer / feedback board.

Main connector voltages are as follows…
RAIL...............................TV in standby..........................TV On
INV ON/OFF (pin 23).................0.01 V...............cycles between 0 V and 5 V with relay click
[PS] ON/OFF (pin 1)..................0.01 V....................................1.17 V
STB 5.3V................................5.15 V....................................5.13 V
13Vs......................................0.3 V....................................13.03 V
5.3V......................................0.1 V.....................................5.13 V
13Vm.....................................0.4 V....................................12.78 V
DET_5V..................................0.22 V...............cycles between 0 and 2.8-3 V with relay
H_SYNC DC (AC)......................0.04 V (0 V)........................1.71 V (3 V)

CN1806 connector voltages from PS board to inverter driver / balancer board:
RAIL................................TV in standby.......................TV On
Vcc (pin 1)..............................0.07 V.................................10.5 V
LD..........................................0 V.....................................11.55 V
FB1 (DC measurement)...............0.02 mV..............................-0.54 mV when relay clicks on
FB1 (AC measurement)...............0.1 mV......................mostly ~0 mV, but sometimes 30-56 mV on the 3rd or 4th relay click
FB2 (DC measurement)...............0.02 mV.......................-6 mV when relay clicks on
FB2 (AC measurement)...............0.1 mV......................54 to 63 mV with relay clicks on

Other things I checked:
- Voltage on main input caps of the PS board are at ~167V DC when the TV is in standby, and 388.8V DC when the TV in On. Voltage is stable when the relay clicks On.
- Voltage measurement for FB1 and FB2 voltages was done across feedback resistors RF801 thru RF804. These resistors are 22 Ohms each, with RF801 and 802 in parallel (for 11 Ohms total) and 803 and 804 in parallel (for 11 Ohms total, again.)
- Feedback resistors RF801 thru RF804 above are in spec.
- Did a basic resistance + diode check on most feedback components for the inverter on the PS board, and they all appear okay.
- Inverter transformers on the PS board have nearly identical resistance, so they appear to be okay as well.
- Removed TFT panel and checked the CCFL tubes – all tubes light up when the inverter cycles On (i.e. when the relay clicks). None seem to be burned or darkened and they appear the same brightness, as far as I can tell from the quick power cycling.

I also already tried forcing the inverter on by raising the INV ON/OFF pin high, along with PS ON/OFF pin. The power supply voltages come up, and the relay clicks and stays On. But I get no light output from the backlight. I think the E_PWM and H_SYNC signals may have something to do with that, though, because when I ran that test, I had the logic/video board disconnected. Pulling E_PWM both high and low didn’t seem to make a difference.

With all of that said, are there any suggestions what else I should check or perhaps where else I might look? I’m thinking there must be something wrong with the CCFL inverter driver / balancer / feedback board. But I’m not sure what to check on there. Most SMD components measured fine on resistance and diode test. And the transformers on that board are hard to test, because IIRC when I last tested it some months ago, those smaller transformers have very short turns on their outputs and thus always read as nearly short-circuit.

Anyways, the PSU model / part number is IP-261603A [or BN44-00265A], if that’s of any help. I’ll try taking pictures of the driver / balancer and video / logic boards tomorrow. Speaking of the video / logic board – all regulators and MOSFETs measured okay.

Thanks for reading! Hope the TV can get fixed. I don’t really have much use for a second TV, but it’s been sitting around and taking space for too long.

[nomoresonys]

Re: Samsung LN46b530p7f – relay clicks and backlight cycling, sound OK

Possibly bad/faulty transformer on inverter, can be tricky to test, some how to vids. on youtube.

[budm]

Re: Samsung LN46b530p7f – relay clicks and backlight cycling, sound OK

What happen if you disconnect the cable from the power supply board and the main board and then force on the power supply and the inverter circuit?
Can we see the whole backside of the TV showing all the boards? It looks like this TV has Balancer board for the backlights lamps.

[CapLeaker]

Re: Samsung LN46b530p7f – relay clicks and backlight cycling, sound OK

SJ has a kit: Samsung BN44-00265A Power Supply / Backlight Inverter Component Repair Kit

The Samsung BN44-00265A Power Supply / Backlight Inverter Component Repair Kit includes all commonly failing components on the PSU/BLI Board. Symptoms include no power / dead set, slow start-up, no 5V standby, no or intermittent backlights.

Look at the components used in the kit and check it with yours.

[nomoresonys]

Re: Samsung LN46b530p7f – relay clicks and backlight cycling, sound OK

Some testing, if you do it HEED THE WARNING THE VOLTAGE IS DEADLY. I can tell you know what you are doing, the warning is for those who may not be aware of the danger. https://www.youtube.com/watch?v=oE6K4xBVweA

[momaka]

Re: Samsung LN46b530p7f – relay clicks and backlight cycling, sound OK

Thanks for the replies, folks!

What happen if you disconnect the cable from the power supply board and the main board and then force on the power supply and the inverter circuit?

I tried that, and this is the result: PSU secondary outputs and inverter power up instantly. The relay clicks On and stays On as long as the TV is plugged in. The backlights flash once for less than half a second and then shut down. I can repeat this if I unplug the TV from the wall, wait 2-3 seconds for the capacitors to discharge (and relay to click Off), then plug it in again.

With that done, I decided to do another experiment: I made a small pull-up/down circuit with a switch on a breadboard and connected the PSU to that.

Basically, I had the PS ON/OFF signal pulled up to 5V (from STB 5V) with a 510 Ohm resistor. INV ON/OFF and DET_5V I pulled down to ground with 2.7 kOhm resistors and also wired to a switch button - which when pressed, pulls up these rails to 5V (through 100 Ohm resistors) from the 5.3V rail.

This new "setup" allowed me to cycle the inverter On and Off as I pleased when pressing the switch and without having to unplug the TV. So when I did that, the relay for the TV would click On, then the backlights would flash briefly and shut down - just the same way as the above setup. However, de-pressing and pressing the button again to trigger the backlights would make them flash for a shorter period of time after the initial longer flash. If I unplug and plug back the TV, I can repeat the same experiment again.

Worth noting here is that the relay that cycles is RL8015, which simply bypasses the NTC inrush thermistor on the primary side.

Also worth noting is that without 5V_DET pin pulled up, the inverter would NOT power On.

After all of these tests, I tried the TV again connected to the logic board, just to make sure my "experiemnts" above didn't mess anything (well, they shouldn't with those pull up resistors, but I always check) - but everything is the same as before.

Can we see the whole backside of the TV showing all the boards? It looks like this TV has Balancer board for the backlights lamps.

Pictures attached.
Yes, the inverter has a "balancer" board indeed. Model number is ssb460h16v01 and/or inv46b16f. A detailed picture of that is attached in the ZIP file, because it is too wide for the forum image feature to accept it (I stitched it from several images taken up close).
Also attached pictures of the logic board. Model number for that one is bn41-01181a, if I am not mistaken.

Let me know if these pictures are any good or if you need more. And thanks gain for your replies.

BTW, I attached some pictures of the CCFL tubes in the TV as well. None of them look badly burner/darkened at the ends.
There are also two pictures (the last two) of the feedback circuit on the back of the PSU board. There are two ICs on the PSU board that are related to this circuit, I believe: one is a A393F (393 dual comparator) and a LX65031DW 16-pin chip (which I think is the inverter driver on the PSU board).

Some testing, if you do it HEED THE WARNING THE VOLTAGE IS DEADLY.

Thanks for the heads up.
Yes, I'm aware of the dangerous voltages in these TVs, so I'm always careful when I have the set plugged in for testing / voltage measurements. For starters, I always wear my safety glasses (never know if something is gonna blow up in your face) and almost always keep one hand on the power cord plug, ready to unplug it if needed.

SJ has a kit: Samsung BN44-00265A Power Supply / Backlight Inverter Component Repair Kit
...
Look at the components used in the kit and check it with yours.

Very good idea, thank you!

I see the kit includes mostly capacitors and transistors/rectifiers + 2 ICs - most likely to alleviate the issue of a bad power supply (I'm guessing the ICs are the pri.-side PFC controller and pri.-side PWM controllers). Not anything much related to the inverter, though. So probably not my issue, as my power supply voltages are solid and I already did a not-so-great but functional recap.