Asus X555L backlight shuts off when on battery

[sakalaz]

Re: Asus X555L backlight shuts off when on battery

Hi guys, same issue here (I think)
so far I have noticed two things:

1. BL_EN signal going to the LCD is 2.6v not sure if this is normal nevertheless backlight comes on when plugging the charger.

2. AC_BAT_SYS going to LCD when on charger is 19V and after disconnecting the charger it drop to 7.6v (battery voltage). My assumption is that this is the main issue for the backlight not turning on. I would expect the voltage to be in range 12v-19v

Not realy sure where to go from here? Charge controller IC?

[sakalaz]

Re: Asus X555L backlight shuts off when on battery

Just had a look at LCD panel specification that I have (Innolux N156BGE-L31)
Basically all the signals going to the pannel are correct and within the specification.

From specification:
1. BL_EN - backlight enabled voltage range 2.4-3.6
2. Pin38, Pin39, Pin40 - backlight voltage range 6v-21v

So... it must be that LCD logic board that is faulty. Could be the backlight DC boost circuit. I will be checking that today

[Dannyx]

Re: Asus X555L backlight shuts off when on battery

It would be interesting to see how/if you manage to solve this issue. This was slightly before I got really into component-level board repairs, so I lacked the required skills and knowledge to work out stuff like this on my own.

[mcplslg123]

Re: Asus X555L backlight shuts off when on battery

Just had a look at LCD panel specification that I have (Innolux N156BGE-L31)
Basically all the signals going to the pannel are correct and within the specification.

From specification:
1. BL_EN - backlight enabled voltage range 2.4-3.6
2. Pin38, Pin39, Pin40 - backlight voltage range 6v-21v

So... it must be that LCD logic board that is faulty. Could be the backlight DC boost circuit. I will be checking that today

Just replace the coil(marked 100) near backlit IC on led panel. Though weird but works. had this same issue on asus.

See my thread
https://www.badcaps.net/forum/showthread.php?t=76823

[Dannyx]

Re: Asus X555L backlight shuts off when on battery

Hm...wonder if it works on this model too. Guess it depends on what panel you get in your laptop, since I imagine they may differ even between identical models.

[RethoricalCheese]

Re: Asus X555L backlight shuts off when on battery

Yes, it seems to be same on all the Asus xx55y models with this fault. It took two hours of research surfing russian forums to find out about it. (And I don't even speak russian )

[sakalaz]

Re: Asus X555L backlight shuts off when on battery

So I went through the backlight circuit without having a datasheet for CM509A chip and couldn't find anything obviously wrong...

Just replacing the coil sounds not very convincing. Coils are passive components so it is uncommon for them to go bad unless they run hot or windings get shorted. Those LCDs that get "fixed" by replacing the coild could most likely be the cause of heat applied to driver chip or the diode near it (remember graphics chips, tantulum capacitors...) Nontheless I will try replacing the coil as a last try.

Just found someone stating that MP3388 is a direct alternative for CM509A. I will have another galnce at the board now with this information at hand.

Datasheet for MP33388 https://cdn.badcaps-static.com/pdfs/...f57cd8ef3f.pdf

Orderd an inductance meter from aliexpress and a pair of CM509A and MP3388 chips to play with.
This coil is 10 uH I think? Will be interresting to measure it

so next steps:
1. Take the coil off and measure it
2. Change a backlight driver chip to new one
3. Change a backlight driver chip to alternative (MP3388)
4. Change the coil

[RethoricalCheese]

Re: Asus X555L backlight shuts off when on battery

Just an hour ago had another Asus with the same problem. Replaced coil, got it working.

Maybe it is just underdimensioned thus running on its limit and will start acting up after a few years of use.

[sakalaz]

Re: Asus X555L backlight shuts off when on battery

Just an hour ago had another Asus with the same problem. Replaced coil, got it working.

Maybe it is just underdimensioned thus running on its limit and will start acting up after a few years of use.

Is it a 10 uH coil? You take then from a donor PCBs or do you buy them?

[RethoricalCheese]

Re: Asus X555L backlight shuts off when on battery

Since I have a pile of scrap donor displays, I get them from there.

Yes, marking 100 = 10uH.

[Dannyx]

Re: Asus X555L backlight shuts off when on battery

Just an hour ago had another Asus with the same problem. Replaced coil, got it working.

So was your problem similar to mine where there's backlight on AC power only ? Wish I had known of this trick at that time too

[RethoricalCheese]

Re: Asus X555L backlight shuts off when on battery

Yes, exactly the same problem. Seems to be a problem with Innolux panels.

[Dannyx]

Re: Asus X555L backlight shuts off when on battery

Sorry for the late reply. Given that the coil which causes the backlight to shut off when the laptop is running on battery is on the panel itself, it means the problem could also be solved with a new panel entirely, can't it ?

I can understand why nobody would bother to check with a replacement panel, because they'd plug the adapter in, see the picture come on screen nice and crystal clear and think "nope - display must be fine", but it isn't !

Is the backlight driver for these displays located on the panel itself ? I know Louis Rossmann talks about backlight circuits a lot and they're always on the laptop's board and not in the panel itself. It means the LVDS cable carries "B+" to the display which is then stepped up to drive the LEDs...I was curious what sort of voltage one might expect to see on the LVDS connector itself. On Macbooks, the LED voltage itself is present there, which is pretty high.....and dangerously close to the signal lines for the display

[mcplslg123]

Re: Asus X555L backlight shuts off when on battery

A new compatible panel does solves the problem in asus but why replace it if a simple coil replacement solves the problem. The backlit driver is located on the panel itself just near the backlit connector on the screen.

[RJARRRPCGP]

Re: Asus X555L backlight shuts off when on battery

has stopped working

That's the dumbed-down Windows error message, since Vista, meaning it has crashed with an invalid page fault (called an access violation) or another application-related exception detected by Windows.

[Dannyx]

Re: Asus X555L backlight shuts off when on battery

I had no idea what you were referring to, since you didn't include my full quote, so I looked back and found out I was talking about OpenBoardView not working for me Since then, I actually found a different one called OpenBoardViewER and that works perfectly No idea where it came from TBH, but who cares as long as it does its job.

[RJARRRPCGP]

Re: Asus X555L backlight shuts off when on battery

I had no idea what you were referring to, since you didn't include my full quote, so I looked back and found out I was talking about OpenBoardView not working for me

I quoted the "X has stopped working" Windows pop-up.

[Dannyx]

Re: Asus X555L backlight shuts off when on battery

Yeah, it's been a while and I forgot WHAT was not working

[mellbo]

Re: Asus X555L backlight shuts off when on battery

Hello guys. I also have this problem with Asus TP550LD. I would like to order that coil from TME, but I need some small help. I don`t know about curent of the coils. Any guys with TP550LD can confirm about fix with replace the coil in nearing CM509A ?

[Dannyx]

Re: Asus X555L backlight shuts off when on battery

CM509A ?

Is this a capacitor on the LVDS board of the panel ? Just curious...I don't have a panel on hand unfortunately...