LN46A530 Backlights Flash

[neilc6]

TV turns on and off but backlights flash on for a few seconds before going out.

I suspect bad CCFL bulbs and would like to force the backlights on so I can confirm the main board and tcon are good before I salvage the boards and sell them. I did this previously on a LN40B500 following this thread https://www.badcaps.net/forum/showthread.php?t=29580

Don't see an OVP pin from the inverter. Controller IC is different LX1692BIDW PS is BN44-00202A

The 8 pin connector from the inverter board measures.
VCC 12V
FB 0V
FB 0v
GND
LD 12V
LD 12V

so the 12V regulator is good from this thread https://www.badcaps.net/forum/showthread.php?t=55179

Caps on the PS are original and not bulged.

[budm]

Re: LN46A530 Backlights Flash

LD will go below 10V when backlights error occur.
LD (Lamp Detect) 12V is normal so monitor this pin when TV is turned on and see if it drops down or not.
FB is lamp current feedback, it is high frequency AC (your AC Volt meter does not have the bandwidth to read it) and it will be in mACV range.
Pictures of the whole backside of the TV needed. It looks like your TV uses Balancer board.
BN44-00202A: https://www.shopjimmy.com/samsung-bn...wer-supply.htm
https://www.youtube.com/watch?v=oE6K4xBVweA
https://www.youtube.com/watch?v=Dh01ZepjDp0

[nomoresonys]

Re: LN46A530 Backlights Flash

That might help: https://www.youtube.com/watch?v=Dh01ZepjDp0

[neilc6]

Re: LN46A530 Backlights Flash

Monitoring both LD signals, they do not drop when the backlights are on. Also checked INV ON/OFF from the main board. It goes high and stays high (5V).

Other signals on the connector from the main board are PWM DIM and DET_5V.

[CapLeaker]

Re: LN46A530 Backlights Flash

measure the resistance on the secondary side on each transformer on the inverter board and compare them to each other.

[neilc6]

Re: LN46A530 Backlights Flash

Secondary transformer readings: 386, 389, 393, 391, 395, 389, 393, 390, 389, 378, 384, 388, 393, 380, 387, 406, 390, 391, 384, 392, 390, 388, 393, 385

One a little high (406) and one a little low (378)

[budm]

Re: LN46A530 Backlights Flash

The invererter transformers (2) are on the power supply/inverter boards, then you have TWO Balancer boards that distribute the high Voltage to each lamps via the small transformers on each Balancer board..
Also, the lamps are driven in push-pill mode,
SONY Training manual, SONY/SAMSUNG use the same topology since they were working together in the past. Page 49 is to topology used in your TV.
Did you watch the videos? Also read the trouble shooting section.
The LD dropping Voltage may be too fast and too short for your meter to detect.

[CapLeaker]

Re: LN46A530 Backlights Flash

Eek. Thats one of them with a master / slave boards driven by 2 transformers on the PSU. Well, more complicated... however same thing applies to the 2 transformers that supply the juice to the 2 balancer boards. Measure the secondary on those and look for evidence that one transformer runs hotter than the other(s). Check all transformers and the little blue capacitor for cracked solder joints.

[budm]

Re: LN46A530 Backlights Flash

BTW, verify that the PFC boosted Voltage did not drop out.

[neilc6]

Re: LN46A530 Backlights Flash

I probed the Enable pin on the controller IC. It is high and stays high when the backlights go out. PFC voltage is 390VDC and stable with the backlights off. Transformer solder joints look good. Secondary winding resistance on the two transformers are 20 ohms each. I disconnected a random tube and it has the same flash with one tube disconnected.

[budm]

Re: LN46A530 Backlights Flash

It will only take one bad lamp (or disconnected lamp or lamp that will not go into conduction after firing Voltage is applied) to cause the backlights to go into shutdown, you need to test the test point on the Balance board as shown in the video to see if any one of the lamp causes the error output signal as shown in norcal video.

[neilc6]

Re: LN46A530 Backlights Flash

I removed the panel and all the bulbs are good though as bulbs age, they can draw more current causing an overcurrent situation. I don't see test points on the balancer board in the video.

[CapLeaker]

Re: LN46A530 Backlights Flash

do theses ccfls have a pinkish tint?

[neilc6]

Re: LN46A530 Backlights Flash

No pinkish tint. I'm going to go through the power supply schematic and controller datasheet.

[CapLeaker]

Re: LN46A530 Backlights Flash

i am still thinking it's one of them transformers. There is always a transformer pair per ccfl. Usually they can't be far apart. the pair reading 387 on one and 406 for the other would be my suspect.