T430 Backlight dimming = mad flickering

[ketsa]

Hello all,

I recently acquired a T430, it works well for my needs but I have one problem with it :

The screen only works correctly on maximum brightness,
One press on Fn-F8, it strongly dims and starts flickering like mad. unusable.
Further presses on Fn-F8 reduce brightness but still flicker very fast.

It is not an operating system issue as it also happens on the BIOS screen, on windows and on Linux.

Any ideas where it comes from ?

Thanks.

[Screamer]

I suspect that it has something to do with the display panel's backlight or the inverter, but have you tried to reduce the flickering via IntelPWMControl?

If the display panel doesn't show any signs of an aging backlight (strong pink/red tint on boot-up), it could be the inverter that is at fault. If I were you, I would replace the inverter and see how it goes from there.

[RealBlackStuff]

T430 does not have an inverter, which was only used with CCFL backlight.
T430 has LED-backlight, which is supported by the LED-board (see HMM pages 108/109).

[ketsa]

Really ? It looks to me like that small led board is only for the wifi and HDD leds.

[Screamer]

Well, it could be. The panel appears to be solely driven by motherboard's power connector from what the hardware maintenance manual seems to show.

As the inverter's ruled out, I believe the display panel needs to be replaced.

T430 does not have an inverter, which was only used with CCFL backlight.
T430 has LED-backlight, which is supported by the LED-board (see HMM pages 108/109).

My bad, sorry. I was under the impression that a LED-backlit display panel still required an inverter to convert DC to AC, but after thinking that through, it does make sense that the inverter would no longer be needed for a LED-backlit panel.

[Thinkpad4by3]

My bad, sorry. I was under the impression that a LED-backlit display panel still required an inverter to convert DC to AC, but after thinking that through, it does make sense that the inverter would no longer be needed for a LED-backlit panel.

Well it does need a driver...but it's a DC driver. The LEDs are driven at like 27-36V constant current...but it's not an inverter because it isn't going DC->AC.

[ketsa]

I ordered a new LCD panel, we'll see...

[ketsa]

Received a new screen : backlight dimming works so my screen is definitely defect.

But the screen i received has 2 big light/white streaks... now starting RMA.

[a_q]

What about this "LED Board"?

I have a T430 with no backlight (you can see the dim logo on the screen).

I found a LED board on ebay (e.g. part number 94V-0 CN0404) but it doesn't look man enough to be a DC-DC convertor (i.e. drive the backlight)?

It only seems to have a few resistors, caps, diodes and LED's on it.

Does it do this, or is the 36V DC generated on the motherboard?

Thanks.

[RealBlackStuff]

If you have no backlight, then most likely you blew the backlight fuse F3 near the LCD-connector. (ERBRD3R00X - Fuse, Surface Mount, 3 A, 32 VDC, Fast Acting, 0402 )
If so, piggyback-solder a new one on top of it.

[a_q]

Thanks first time I've seen F3 mentioned, previously it was F7 (which is OK)/.

F3 is indeed open circuit and it's on the top of the board so no need for much disassembly, if you can get the iron tip in there.

Thanks again.

[a_q]

D'oh! These 0402 components are ridiculous (and I work with them professionally too.)

F3 and F19 are both OK - read 0 ohms. Given that there's an F19 one question is where are F1, F2, F4-6, F8-F18?

Anyhow the hunt is still on for the fault. Is the boost convertor for the backlight on the motherboard?

[RealBlackStuff]

0 ohms?
You need to check a fuse for continuity, most multimeters nowadays give a buzz or beep if the fuse is OK.
If not OK, you hear nothing.

[a_q]

Last time I looked, zero ohms is continuity. You weren't thinking "infinite ohms" were you?

[a_q]

Looks like the root cause was a loose cnnector behind the screen. This looks like poor design as there is nothing retaining it.

Anyhow in the mean time the screen itself has developed a fault so I am looking at swapping it out.

The one in there is a B140RW02 AUO (40-pin connector), does anyone know if I need to stick with the N/W:3A F/W:1 designation or are they all pretty much interchangeable?

As the price of secondhand replacements varies considerably, if I can pick and choose I can save a lot of $$$ £££.