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Equipment Repairs => LCD TV forum => Topic started by: brooksy05 on July 08, 2015,21:10:28
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Hi all
I have a TV that's throwing a bl_sos error
The unit powers up OK, but the back light flickers like a florescent light for a bit then it throws the error.
I have checked for the obvious things like bulging caps hot marks on the boards and all look good, all voltages check OK on the psu
Ant tips on parts to check/replace next?
Any help would be greatly appreciated
P.S im not a tec but do know how to use a multi meter
Cheers brooksy
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:sign0144: :sign0085:
Link to manual if anyone wants to have a look
http://www.tv.quuq.org/index.php?ind=downloads&op=entry_view&iden=1471 (http://www.tv.quuq.org/index.php?ind=downloads&op=entry_view&iden=1471)
The pwm input on the LG board what's it's purpose?
Would I be correct in thinking that It controls back light brightness?
If so with the all voltages to the board being correct
the problem must lie in the LD board.
any input welcome even negative :thumbup:
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Hi brooksy05,
Take a ganger at this service bulletin. It may be your problem.
Bruce
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Thank you Sir :brinda:
The problem it covers is not so much the problem I have but it's something to investigate
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Are the voltages at connectors LD1 and LD3 on the LED Driver (LD) board constant, or are they fluctuating all over the place. My gut feeling is that you have faulty LEDs inside the panel, but you would need to disassemble the display panel to check these. Not really a job for beginners, as it's easy to fracture the thin panel.
Bruce
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The 24v to the LD board is solid so is the 16v not that it looks to go anywhere. It's the Bl_on line (pin 2 LD1) that's flucuating.
So that leads me back to the A board
I'm trying to wrap my head around the 18 pages of Schematics for it to get a feel for what's where and so forth
Worst part is none of the test points are labeled on the board. They are in the manual in the circuit board pic's but pixelate to bad to read them :41:
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KM21E
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Problem may well be A-Board if BL-ON is all over the shop, as that's where the BL-ON is generated.
Can you disconnect the BL-ON line, or cut it, and connect it via a 100 ohm resistor to the STB-5V (or 3V3) as a substitute for the BL-ON voltage. If the backlights come on without flickering, then you'll know the A board is the offender.
You are correct in that the 16V to the LD board is not used.
Bruce
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I'm More confused now
Jumped Power to the BL_on pin of the LD board and it still flashes and throws a error.
With nothing on the BL on pin the unit starts up fine with no errors
And when you stick the meter on the BL on line it holds steady
I'm close to screwing it back together and putting it in the shop
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And thanks Jordan the power board is the same in that one
And most of the circuit is the same but the A board itself is different :c017:
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In my opinion, then, you have LED backlight problems. Maybe a faulty connection in the LED strips or wiring.
At this point the TV is useless other than for parts. You could attempt to disassemble the display panel and check. Look for any burn marks firstly.
Bruce
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With the back light connector disconnected
From the board it's the same thing.
I thought that would eliminate the back light from being the cause?
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Well, not necessarily. If the micro detects the absence of the backlights, it most likely give you the same error code.
For what it's worth, I've uploaded the TH-L50B6A service manual to the "Downloads" area of this forum.
Bruce
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I download it before posting on the forum
In fact That's how I found the forum.
With the back light disconnected the BL_ON line still fluctuates
For 5 seconds before it faults and throws the error
I might power the back light with the bench top supply and see how I go
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OK, try this. Remove the connector on the A-Board that comes from the P-board. On that free plug, locate STB-5V and PS-ON and insert a small 100 ohm resistor into the plug pins between these two. Do the same between STB-5V and BL-ON. Plug the tv in. Now that you've cheated those 2 control lines, the P-board should operate all its working voltages and the backlights should work.
If all is sweet at this point, you can blame the A-Board for your woes. If backlights still flicker, and all the P-Board volts are stable, you can blame the LD-Board or the LED backlights. Not sure how you pick between these two. I usually strip the display and check the LED strips inside for burnt LEDs or connections,etc.
Bruce
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So I can confirm its not the A board
All voltages stable from the P board
The output from the Ld board to back light pulse up and down
with or without back light hooked up. I took a plunge and split the screen ( I have done many phones) and all leds look OK.
So now where is the best place to find parts the 2 local shops haven't been to keen to order parts in before for me
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So what have you decided, LD board?
Panasonic spares are supplied by Statewide Appliance Spares or JNG. Get the correct part number from the service manual.
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Yes Ld board, what on the board I don't know.
I wish at time like this I finished my traineeship when I got out of school.
I had the fets off the board and they seem to test OK, so I will try find out a price on a new LD board and see if it's worth the money to fix. It was a free TV, so easy come easy go
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https://www.google.com.au/url?sa=t&source=web&rct=j&ei=81eiVYjqGsHwmAXj64D4BQ&url=http://www.semicon.sanken-ele.co.jp/sk_content/bl0200c_ds_en.pdf&ved=0CBsQFjAA&usg=AFQjCNHnuK7A-s56rvTMihH5L5zo1eVs4Q (https://www.google.com.au/url?sa=t&source=web&rct=j&ei=81eiVYjqGsHwmAXj64D4BQ&url=http://www.semicon.sanken-ele.co.jp/sk_content/bl0200c_ds_en.pdf&ved=0CBsQFjAA&usg=AFQjCNHnuK7A-s56rvTMihH5L5zo1eVs4Q)
Link to data sheet for the main ic on the LD board
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What's the chances of the LD board from a tx-l50b6b
Working in this TV?
See attached manual
The P board and LD board schematics look to be the same
And I can get the board cheep from the UK
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Didn't have time to study the P-board, but the LD-board look identical circuit-wise. Some difference in the part number but I guess it's for a different market. Worth a shot.
Bruce
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Well the replacement LD board has been ordered and should be on its way. I will let you know how it goes.
I must say a big thanks to you Bruce for all your help :1st:
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Another tech having similar problems tells me the LD board is NLA.
Bruce
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Yeah that's what I found to
I got one from the UK, form the
Tx-l50b6b unit I posted the manual for.
the schematic all looks the same, photos of the board are the same. Number on the board tnp4g549 the same just different part numbers in the manuals.
So I'm confident it's going to work as it should
Only difference is it has the difference caps that the service bulletin you posted installed already.
But then someone with better knowledge may be able to fix the board
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Hi guys. Sorry to revive an old thread but, I'm having the same issue (flickering backlight) with same model (TH-L50B6A) and need to ask, replacing the LD board fixed the issue? Also is the service manual still available as I cannot see it in the download section. Cheers!
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Hi Dan.
I have uploaded the service manual to the download section. Backlight failure seems common on this model - uses a LG panel - but this invariably activates a error code of 1.
Check these voltages on the LD Board for stability. At connector LD1, BL-ON at pin2 and 24V supply at pins 8,9,10. At LD3 (output),
pins 1 and 5 are the LED drive voltages.
A pity brooksy didn't follow up but I have to say my gut feeling is an iffey panel (LEDs). Bruce
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Hi Bruce.
Thanks for your prompt reply and also for uploading the service manual again.
I will do as you have mentioned and report back with my findings, only due to work commitments, I wont get a chance to do anything until midweek :(
Regards!
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OK so it wasnt easy testing these voltages on my own because once the TV throws the error (green light goes out, red starts flashing) I have to put the tester down to unplug and plug back in the TV mains every 5 seconds or so. Ive tested the at connector LD1, BL-ON at pin2 (fluctuating between 0 to 3.2V) and 24V supply at pins 8,9,10 (all have 24V +or- <0.5V) And at LD3 (output), pin 1 (fluctuating between 9 to 14V) and pin 5 (nothing at all).
I've been searching for an unicorns err LD Boards, found one, second hand, selling for more than Id like to spend on S/H. So hoping it may be something else causing this problem.
Next step?, disconnect the BL-ON line, or cut it, and connect it via a 100 ohm resistor to the STB-5V (or 3V3) as a substitute for the BL-ON voltage. Only problem is in the schematics I cannot tell which is the STB-5V (3V3) :(
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What about using an external power supply......a couple of 1.5V batteries perhaps. The output at LD3 is definitely screwed up.
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Problem may well be A-Board if BL-ON is all over the shop, as that's where the BL-ON is generated.
Can you disconnect the BL-ON line, or cut it, and connect it via a 100 ohm resistor to the STB-5V (or 3V3) as a substitute for the BL-ON voltage. If the backlights come on without flickering, then you'll know the A board is the offender.
You are correct in that the 16V to the LD board is not used.
Bruce
Hi
can you please elaborate this in easy words please.
thanks
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I'm More confused now
Jumped Power to the BL_on pin of the LD board and it still flashes and throws a error.
With nothing on the BL on pin the unit starts up fine with no errors
And when you stick the meter on the BL on line it holds steady
I'm close to screwing it back together and putting it in the shop
Can you please explain how did you jump the BL_ON I'm kinda noob here.
Please help
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