Acer Aspire V5-431 no backlight

[PanicMechanic]

https://www.badcaps.net/forum/showthread.php?t=75984

Same laptop, same issue (display works, but no backlight).

I get this voltages on the display driver board connector (for the backlight, I assume):



What voltages should I get?

BTW, the posted schematics does not help. Backlight power page is blank.

LCD panel: B140XTN02.4

LCD driver board: TCM14F32

[mon2]

Re: Acer Aspire V5-431 no backlight

See attached.

Locate the 30 pin display connector.

You may be missing the backlight led voltage that should be present on 3 pins of this 30 pin connector. Check the fuse that should precede connector.

[PanicMechanic]

Re: Acer Aspire V5-431 no backlight

BL_Enable is 3.3V (pin 22 on the LCD-side connector)
BL_PWR is 0V (pins 27, 28, 27 on the LCD-side connector).

The resetable fuse is OK.

So the 12V power supply on the motherboard is the issue, not the LCD driver board.

[PanicMechanic]

Re: Acer Aspire V5-431 no backlight

The problem is here somwhere:



There is a burtn ceramic cap, but there is still 19V on it (from the power adapter).


EDIT: Nah, that is a battery charge controller circuit... :/

[PanicMechanic]

Re: Acer Aspire V5-431 no backlight

Don't know which part of the circuit generates 12V for the backlight.

[mon2]

Re: Acer Aspire V5-431 no backlight

Ok, some chaos here. The backlight voltage is fed from the logic board but that portion of the schematic is missing.

In checking other 30 pin eDP display connectors on the Acer Aspire series, found that the same set of pins are with a netname of VIN.

VIN is the main voltage rail that powers the logic board.

Remove all power -> meter in lowest resistance mode -> one meter probe on the backlight voltage pin on the display connector. Other meter probe to the main 19v power rail (after the 2 x DCin mosfets or similar).

What is the resistance ? if the resistance is ~0 ohms then this backlight feed is ~19v when it is working.

Post your resistance measurement.

[mon2]

Re: Acer Aspire V5-431 no backlight

In hindsight, since you have no voltage on the 30 pin eDP connector, you most likely will not have a trace from the fuse to the VIN rail.

Post a close pic of this area where the fuse resides.

The work around may be to shift the fuse so that one pad connects to the eDP power pins (3 pins used for the backlight).

The OTHER side of the fuse to connect to the main VIN power rail using a piece of wire. Before you do this, we want to be 110% sure that the fuse is not mating to any other parts that are nearby.

In summary, you just need a power rail that is high enough for the eDP panel to accept and the panel will do the rest. That is my understanding. If this power rail is absent, the backlight will be OFF.

[JaroTech]

Re: Acer Aspire V5-431 no backlight

Hi, a simple question, depending on the motherboard you have, how many pins do you have on the LCD connector on the motherboard?

[mon2]

Re: Acer Aspire V5-431 no backlight

It will vary by the design of the logic board - there is the 30 pin and 40 pin versions of the LCD connectors. This is common to laptops.

For portable (mobile) phones, it is MIPI. MIPI is a high speed differential signal transfer so they are applied in pairs.

Lower resolution mobile phones are featuring:

MIPI_LANE0 ; a pair of connections from logic board to target display
MIPI_CLK ; a pair of connections from logic board to target display to clock out the data

The LANEx count increases as the display resolution increases.

For example, the more current iPHONES will be 4 MIPI LANES + CLOCK pair.

[JaroTech]

Re: Acer Aspire V5-431 no backlight

Ok, but how many pins on this Acer Aspire V5-431?

[mon2]

Re: Acer Aspire V5-431 no backlight

30 as shown in the schematics which are on this forum.

The backlight circuit is not present in the same schematics.

[JaroTech]

Re: Acer Aspire V5-431 no backlight

How come on page 49 of the schematics, the connector LCD1 has 40 pins?

[mon2]

Re: Acer Aspire V5-431 no backlight

The OP noted the display is LCD panel: B140XTN02.4.

Datasheet for the display is posted above.

This display has 30 pins = eDP. Then checking other Acer models with eDP to review how they source the backlight voltage rail.

[PanicMechanic]

Re: Acer Aspire V5-431 no backlight

Ok, some chaos here. The backlight voltage is fed from the logic board but that portion of the schematic is missing.

In checking other 30 pin eDP display connectors on the Acer Aspire series, found that the same set of pins are with a netname of VIN.

VIN is the main voltage rail that powers the logic board.

Remove all power -> meter in lowest resistance mode -> one meter probe on the backlight voltage pin on the display connector. Other meter probe to the main 19v power rail (after the 2 x DCin mosfets or similar).

What is the resistance ? if the resistance is ~0 ohms then this backlight feed is ~19v when it is working.

Post your resistance measurement.

It is not 0 Ohms. It is a few kilohms, around 0.5 Mohms and chnagning (some capacitance charging).

In hindsight, since you have no voltage on the 30 pin eDP connector, you most likely will not have a trace from the fuse to the VIN rail.

Post a close pic of this area where the fuse resides.

The work around may be to shift the fuse so that one pad connects to the eDP power pins (3 pins used for the backlight).

The OTHER side of the fuse to connect to the main VIN power rail using a piece of wire. Before you do this, we want to be 110% sure that the fuse is not mating to any other parts that are nearby.

In summary, you just need a power rail that is high enough for the eDP panel to accept and the panel will do the rest. That is my understanding. If this power rail is absent, the backlight will be OFF.

I will try feeding the 19V from the fuse to the BL_PWR, but the 19V is always present (as soon as the power adapter is pluged in).

[PanicMechanic]

Re: Acer Aspire V5-431 no backlight

OK, I have connected 19V to the BL_PWR, and it now works. It lights up when the power button is pressed, as it should.

Now, when laptop is in safe mode, the display works fine.

But when it boots up in normal mode, the display does not work good at all. You can barely see some shapes, it is unusable.

I think it is a graphics driver issue. It's not my laptop, so I don't know.
But if it works fine in the safe mode, then the display is fine.

Thanks for the help.

[mon2]

Re: Acer Aspire V5-431 no backlight

https://community.acer.com/en/discus...000-or-hd-4000

Locate the best driver for this box from Acer or Intel's website.

Do not select too high of a refresh rate or resolution that can distort the display.

Also, is the backlight fuse still present with this bypass hack for the backlight ?

If you are applying the backlight wire direct to the lcd connector, then remove the backlight fuse and test again. Monitor the backlight voltage when the display is in safe mode vs. normal windows mode.

Likely the graphics driver is in a wrong screen refresh or resolution setting.

[PanicMechanic]

Re: Acer Aspire V5-431 no backlight

The fuse is present. It is the main fuse, that goes directly from the pin 1 of the connector on the motherboard, and is fed by the 19V from the power adapter.
I will report back on Friday.

[PanicMechanic]

Re: Acer Aspire V5-431 no backlight

Yeah, the driver was the problem. Windows reinstalled, and it now works in normal mode as well.