Samsung LN46C630K1F – Intermittent Backlight, BN44-00341B Power Board

[nomoresonys]

Re: Samsung LN46C630K1F – Intermittent Backlight, BN44-00341B Power Board

well just to test, turn the backlights all the way up and let it run for a while, see if it fails.

[C152Heavy]

Re: Samsung LN46C630K1F – Intermittent Backlight, BN44-00341B Power Board

well just to test, turn the backlights all the way up and let it run for a while, see if it fails.

Hmmm.... Is the idea to provoke the protection circuit and shut down the TV or to see if the BL fails on the next on/off cycle?

Thanks,

C152Heavy

[nomoresonys]

Re: Samsung LN46C630K1F – Intermittent Backlight, BN44-00341B Power Board

crap my bad, forgot for a second that its ccfl instead of led lighting so prolly won't work.

[C152Heavy]

Re: Samsung LN46C630K1F – Intermittent Backlight, BN44-00341B Power Board

Update:

Since it's been back in service the BL has failed once and wouldn't light for a few ON/OFF power cycles so I pulled the mains plug plus hit the "on" button which drains the two 100u/450V caps/residual power in the system and it has been behaving since.

No idea why that should help and no idea if it would again but it's about all I could do at that point!

Too bad these things don't have a OBD like cars, LOL!

D

[nomoresonys]

Re: Samsung LN46C630K1F – Intermittent Backlight, BN44-00341B Power Board

you mean holding the power button for 30 seconds actually fixed it. seems to be the case, and some said that it did absolutely nothing and never fixed any tv, well looks like they were WRONG.

[C152Heavy]

Re: Samsung LN46C630K1F – Intermittent Backlight, BN44-00341B Power Board

you mean holding the power button for 30 seconds actually fixed it. seems to be the case, and some said that it did absolutely nothing and never fixed any tv, well looks like they were WRONG.

LOL! Well, sort of, not really.

All I did was press the button a few seconds as if I was starting the TV. I had noted previously, when I had test leads on the two 100u/450 caps, doing that drained those caps leaving no residual energy on the board.

So, no attempts at "magic" repairs.

C152Heavy

[nomoresonys]

Re: Samsung LN46C630K1F – Intermittent Backlight, BN44-00341B Power Board

Right not magic, there is science behind it, i researched it.

[C152Heavy]

Re: Samsung LN46C630K1F – Intermittent Backlight, BN44-00341B Power Board

Right not magic, there is science behind it, i researched it.

Ummmm..., Sorry, I'm not getting whether you're joking on serious....

C152Heavy

[nomoresonys]

Re: Samsung LN46C630K1F – Intermittent Backlight, BN44-00341B Power Board

not joking, there was a little debate a while ago, I said the technique fixed certain conditions and some said it did nothing ever.

[R_J]

Re: Samsung LN46C630K1F – Intermittent Backlight, BN44-00341B Power Board

When the tv was unplugged were you still getting standby voltage to supply the main board?

The two main capacitors CP802 and CP803 have resistors in parallel to drain the voltage, RP802,RP805,RP807.RP810 and RP819/RP820 Approx. 6Meg of resistance.

If you are having a intermittent backlight it is likely a poor connection on the high voltage distribution board in the panel.

[C152Heavy]

Re: Samsung LN46C630K1F – Intermittent Backlight, BN44-00341B Power Board

not joking, there was a little debate a while ago, I said the technique fixed certain conditions and some said it did nothing ever.

OK, what is the "magic" procedure? Pull the plug, hold the remote start button down for 30 seconds? Once the capacitors drain (almost instantly) isn't the button hold time not relevant?

What is supposed to be occurring when the button hold procedure is done? Some sort of a mini re-set?

I'm not trying to be smart here, just wanting to understand what's being achieved.

Thanks,

C152Heavy

[C152Heavy]

Re: Samsung LN46C630K1F – Intermittent Backlight, BN44-00341B Power Board

When the tv was unplugged were you still getting standby voltage to supply the main board?

The two main capacitors CP802 and CP803 have resistors in parallel to drain the voltage, RP802,RP805,RP807.RP810 and RP819/RP820 Approx. 6Meg of resistance.

If you are having a intermittent backlight it is likely a poor connection on the high voltage distribution board in the panel.

On 12 Jan., R_J said:

If the backlights have a problem, they can send a signal to the LAMP_DET line

You may have a bad ccfl or there may be a bad connection on the high voltage distribution board in the panel.

Thinking back, I looked around the HV transformers on the Power Board (solder joints) and didn't see anything suspicious. I was looking at the distribution board for bad CFLs etc. and I didn't see anything else that stood out but I wasn't looking specifically for bad connections so I'll put that on the to do list, thanks for the reminder.

Are we looking for a bad connection that keeps the current from flowing to or on the distribution board? Any specific locations/components? Would a bad connection (low voltage) flag a signal on the LAMP_DET line? Would this shut off the backlight or the whole TV? The TV stays on with no BL. Of note is that the BL has never shut off while the TV is on, only failed to start when the TV starts up.

Would unplugging the 2 pin HV cable (Power to HV Dist Board) at the power board simulate the bad connection failure that you suspect? I'm assuming that would simulate a bad connection which would result in the TV booting but with no backlight. Is there any risk of causing damage to do this test? Is there anything useful to learn by doing this test?

You asked about the standby voltage with the TV off and the power cord pulled. I see the standby of 149V and dropping, consistent with what you say about it bleeding off and what I posted back on 11 Jan. and as pasted below:

My posting of 11 Jan:

I have read BUDM's comments about drift of the four 1.5M SMT resistor chain (RP 802, 805, 807, 810) so they are suspects but by his comments I would expect lower CP803/803 voltage. At caps CP802/803 I get 385 V when the BL is on and when it fails to light I get ~159V. At rest, TV off, the voltage is about 149V. BUDM calls for 390V but is 385V close enough?

Of note, when the BL fails to light, the voltage at CP802/803 drops to zero then jumps to ~350V then drops to ~159V. Under normal operation the Cap Voltage is resting between 385 & 149 and simply rises to 385 when the TV boots. I have obtained that data using a Fluke 77 and an older analog meter.

I should add clarification to my comments above regarding the at rest cap voltage with the TV plugged in. Immediately when the TV is turned off the CP802/803 voltage is ~385V and it eventually settles to ~149V. I can't recall specifically watching from 149V to eventually 0V after I unplug the TV but that's what I would expect. It does immediately go to 0V when the remote ON button is pushed so I think the round about answer to your question today is that the main board still has power right after the TV is unplugged. It seems logical since it would be the main board that would detect or receive the detect signal from the remote (IR) sensor and try to boot the TV.

I'm going to make the leap of faith and say the main board still has power for at least a period of time.

Last observation is that the BL has not failed to light since the last event I spoke of on 22 Jan. so data has been slim.

Thanks for your time & comments!

C152Heavy

[nomoresonys]

Re: Samsung LN46C630K1F – Intermittent Backlight, BN44-00341B Power Board

its a hard reset and also drains capacitors etc, and THAT can fix many issues, used for pc's, dvd players all kinds of devices, not magic at all, just electronics.

[C152Heavy]

OP Update:

I see that it's been almost exactly a year since I last posted but I have news worthy of an update. So many of these threads just go quiet, like this one, with no eventual outcome reported but I think I owe it to all that have helped with advice along the way and those attempting to solve the same problem to report back on the final outcome.

I FIXED IT! (Hopefully for good) 😀😁😄😎

If you've read this thread this far then you have seen everything I have done to try and fix this thing. In the past year we have been tolerating the not infrequent failure of the backlight to light but it never completely failed. I just lost patience with it and decided to try the last thing that was suggested but I had not yet tried. That would be to replace those 4 resistors (1.5M, RP802, 805, 807, 810) and the 39K RP819 which BudM recommended. I had shied away from that because I thought the voltage at the 100u/450V power caps (CP802/803) was probably close enough (385 vs 390V) so it was unlikely to be the problem. It was also a reflection of my inexperience in changing SMT resistors but I built sufficient skills and had a go at it.

For my trouble I was left with no backlight at all. I then tried opening the JP852 jumper which has been mentioned but that only got me a quick blink on startup so I put it back.

Finally, as a nothing to lose attempt and with the thought that the new, nominal value resistors broke the backlight completely I theorized that perhaps a resistance value different from the original nominal might help. To achieve this, I replaced RP819 (39k) with a Bourns 50k trimpot, initially set to 39k Ohm. At first I got a blinking backlight, then when I tweaked the value down it became steady at 31k Ohm. Right now the TV is back together and on probation but it starts every time which is a huge improvement.

So, at this point I have one more question, is there any reason this might not be a long term/permanent fix? I find it curious that replacing the 5 resistors with the correct (1%) value did not fix it but an off-nominal value did. Also, is this an indication that a different component is drifting and should be looked at? I don't have a 31k SMT resistor so I left the trimpot for now or maybe for good.

In any case, a big thanks to everyone that contributed to this thread and all the others that I have read while working on this TV!


EDIT: I mentioned that the TV was on probation.....turns out that after 10 - 20 minutes (when I had my back turned, LOL!) the backlight drops out, apparently due to a protection circuit. It comes back after a re-start.

After a little adjustment of the trimpot I now have it so that the backlight keeps working indefinitely, or at least a few hours as of this morning. The updated setting is 36.8k Ohm, closer to the original 39k of the SMT resistor.


C152Heavy 😎

[nomoresonys]

Prolly something similar to what they're yakking about in this thread: https://www.badcaps.net/forum/troubl...is-good?t=8259

[C152Heavy]

Prolly something similar to what they're yakking about in this thread: https://www.badcaps.net/forum/troubl...is-good?t=8259

Thanks, that's an interesting thread. I'll file that away in case I have a CFL that goes west.

Just to underline though, the resistor I'm speaking of is part of the PFC circuit not at the CFL board so I don't think the thread is directly applicable.

D 😎

[nomoresonys]

No expert, but I think it has to do with the old ccfl's gradually going south or west and triggering a shutdown, seems the resister mod balances out the protection so it doesn't get triggered and shutdown, maybe one of the supertechs will chime in about it.

[C152Heavy]

No expert, but I think it has to do with the old ccfl's gradually going south or west and triggering a shutdown, seems the resister mod balances out the protection so it doesn't get triggered and shutdown, maybe one of the supertechs will chime in about it.

At this point I wouldn't be surprised, that seems to make sense. One end of the adjustment range does indeed seem to trigger the protection circuit while the other leads to blinking & drop-out.

On reflection I think there's going to be a replacement TV in our future, it's been interesting and a learning experience which is a lot of what this is about but probably time to cut bait. Since I just can't leave well enough alone, (LOL!) I'm contemplating an LED backlight retrofit just for the fun of it but that would make it a secondary TV, not the primary that has to be depended on. That would become Project 42.

C152Heavy😎

[nomoresonys]

It may run a long time with the adjustable resistor, as long as nothing is getting hot, I don't see why it wouldn't.