Panasonic TH-L50B6A

[brooksy05]

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

[brooksy05]

  
Link to manual if anyone wants to have a look
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

[downunder]

Hi brooksy05,

Take a ganger at this service bulletin. It may be your problem.

Bruce

[brooksy05]

Thank you Sir 
The problem it covers is not so much the problem I have but it's something to investigate

[downunder]

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

[brooksy05]

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

[jordan]

KM21E

[downunder]

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

[brooksy05]

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

[brooksy05]

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  

[downunder]

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

[brooksy05]

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?

[downunder]

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

[brooksy05]

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

[downunder]

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