Acer Aspire R3-131T no backlight

[CambridgeMart]

I'm trying to repair an Acer R3-131T which has display problems. The panhel is working as I can see an image if I hold a bright ligtht up to it, but the backlight is dead. I've checked the signhals on EDP1 and I have +16V on 37-40, +3.2V on eDP_BLEN_CON (pin 34) and +0.5V on eDP_BLCTRL_CON (pin 35).
I don't know what signal levels should be on 34 and 35, so not sure if I should be fault finding the mainboard or the display.

[Techtiger]

Re: Acer Aspire R3-131T no backlight

I'm trying to repair an Acer R3-131T which has display problems. The panhel is working as I can see an image if I hold a bright ligtht up to it, but the backlight is dead. I've checked the signhals on EDP1 and I have +16V on 37-40, +3.2V on eDP_BLEN_CON (pin 34) and +0.5V on eDP_BLCTRL_CON (pin 35).
I don't know what signal levels should be on 34 and 35, so not sure if I should be fault finding the mainboard or the display.

Check LCDVDD 3.3V

[Vesko356]

Re: Acer Aspire R3-131T no backlight

+0.5V on eDP_BLCTRL_CON (pin 35).

Here is the problem, should be 3.3V, so to speak if you short eDP_BLEN_CON with the eDP_BLCTRL_CON the backlight will turn on (but don't do it, just find why eDP_BLCTRL_CON is low).

[CambridgeMart]

Re: Acer Aspire R3-131T no backlight

Here is the problem, should be 3.3V, so to speak if you short eDP_BLEN_CON with the eDP_BLCTRL_CON the backlight will turn on (but don't do it, just find why eDP_BLCTRL_CON is low).

Thanks, that's what I needed to know.

[CambridgeMart]

Re: Acer Aspire R3-131T no backlight

eDP_BLCTRL_CON is low because eDP_BLCTRL_CPU is low, now I am stumped because I can't track the signal back further than R5227 as the next point that the signal surfaces at is below the CPU package.

Update, I managed to locate the trace at the unoccupied R804 pad, eDP_BLCTRL_CPU is low there as well.

[Vesko356]

Re: Acer Aspire R3-131T no backlight

eDP_BLCTRL_CON is low because eDP_BLCTRL_CPU is low, now I am stumped because I can't track the signal back further than R5227 as the next point that the signal surfaces at is below the CPU package.

Update, I managed to locate the trace at the unoccupied R804 pad, eDP_BLCTRL_CPU is low there as well.

Check all resistors and fets in eDP_BLCTRL_CON and eDP_BLCTRL_CPU and resistance to ground in lines, disconnect screen cable (remove the battery and charger first) and measure again. Check hall sensor.

[CambridgeMart]

Re: Acer Aspire R3-131T no backlight

LID_CLOSE1# and LID_CLOSE2# read high with the lid open which appears to be correct if I'm reading the datasheet for the Hall sensor correctly.
eDP_BLCTRL_CPU reads 230k to gnd, so no sign of a problem there (readings taken with the panel disconnected). The FET Q5202 and bipolar Q5203 appear to be functional.

[Vesko356]

Re: Acer Aspire R3-131T no backlight

LID_CLOSE1# and LID_CLOSE2# read high with the lid open which appears to be correct if I'm reading the datasheet for the Hall sensor correctly.
eDP_BLCTRL_CPU reads 230k to gnd, so no sign of a problem there (readings taken with the panel disconnected). The FET Q5202 and bipolar Q5203 appear to be functional.

Will be a dood idea to uplead datasheet here, so if anyone wants to help to see it.
Readings with the panel connected (let me remind you once again - remove the battery and charger when connecting or disconcerting screen)? Did you check all resistors in lines for match with the datasheet values?

[CambridgeMart]

Re: Acer Aspire R3-131T no backlight

All the resistors check out with the values on the schematic. The voltage readings on eDP_BLCTRL_CPU, Q5203 and Q5202 are all exactly the same with the panel connected. I also checked the Hall sensor with a magnet and confirmed the LID signals do change, going low when the magnet is brought near the sensor. It seems the output from the CPU isn't correct.
Datasheet for the Hall sensor is attached.

[Vesko356]

Re: Acer Aspire R3-131T no backlight

All the resistors check out with the values on the schematic. The voltage readings on eDP_BLCTRL_CPU, Q5203 and Q5202 are all exactly the same with the panel connected. I also checked the Hall sensor with a magnet and confirmed the LID signals do change, going low when the magnet is brought near the sensor. It seems the output from the CPU isn't correct.
Datasheet for the Hall sensor is attached.

Come ooon, I meant to upload the whole datasheet, not just the Hall sensor one.
Anyway if we're looking the same datasheet eDP_BLCTRL_CON comes from eDP_BLCTRL_CPU_R, and eDP_BLCTRL_CPU_R comes from 3D3V_S0, so check that line and the resistors (RN5257 and R5220) in it.
So to speak when the laptop is ON 3.3V shold be present in that line, and the line is:
3D3V_S0--->RN5257--->eDP_BLCTRL_CPU_R--->R5220--->eDP_BLCTRL_CON
Simple as that.

[CambridgeMart]

Re: Acer Aspire R3-131T no backlight

Come ooon, I meant to upload the whole datasheet, not just the Hall sensor one.

Oh, you mean the schematic, I'll put it up a little later.


OK, so eDP_BLCTRL_CPU_R is being held low by Q5202 because pin 5 is high as a result of Q5203 being off; Q5203 is off because eDP_BLCTRL_CPU_Q is low due to eDP_BLCTRL_CPU being low.

[CambridgeMart]

Re: Acer Aspire R3-131T no backlight

Acer R3-131T (Wistron Chopper 1-14299-1) schematic.

[Vesko356]

Re: Acer Aspire R3-131T no backlight

Acer R3-131T (Wistron Chopper 1-14299-1) schematic.

Yea, now it's better.
You mentioned that you checked all the fets and resistors, give the measurement results.
I don't know why we hang around for so long, this is not a complicated case, the fault can be detected quickly, in my opinion the fastest way will be this - unsolder RN5257 and take voltage measurements on pins 5.7 and 8, and everything will become clear.

P.S. After that and in case eDP_BLCTRL_CPU is really missing (low) and R5227 is ok, solder back RN5257 and there is nothing to do but to unsolder pin 3 (Q5202), so at least you can have a backlight and be able to use the laptop.

[CambridgeMart]

Re: Acer Aspire R3-131T no backlight

My measurements around Q5202 and Q5203:
Q5202 G2 (5) 3.3V, S2 (4) 0.0V, D2 (3) 0.0V
Q5203 B 0.0V, C 3.3V, E 0.0V

With R5257 removed, its pads measure:
5 0.0V, 7 3.3V, 8 3.3V

So eDP_BLCTRL_CPU is really missing (low) and R5257 is OK, so I'm no further forward! Resistance readings on eDP_BLCTRL_CPU indicate that the trace is connected to the CPU, so I suspect something else is amiss; I'm now contemplating setting eDP_BLCTRL_CPU permanently high as you suggest.

[Vesko356]

Re: Acer Aspire R3-131T no backlight

... 5 0.0V...

Yea, quite a bad news unfortunately.

...and R5227 is ok..

...and R5257 is OK...

R5227 - how much is the measured value in Ohms? Also measure voltage drop (diod mode) both sides to ground.

I'm now contemplating setting eDP_BLCTRL_CPU permanently high as you suggest.

I do not see another solution (but first tell me the R5227 measurements values), at least you will be able to use the machine.

[janifaisal538]

Re: Acer Aspire R3-131T no backlight

I need bios of this mode.. can anyone plz give me org dump of this model?

[Vesko356]

Re: Acer Aspire R3-131T no backlight

I need bios of this mode.. can anyone plz give me org dump of this model?

Create your own topic at "BIOS Requests ONLY!" section, but use forum search first:

https://www.badcaps.net/forum/showth...hlight=R3-131T

https://www.badcaps.net/forum/showth...hlight=R3-131T

[Vesko356]

Re: Acer Aspire R3-131T no backlight

LID_CLOSE1# and LID_CLOSE2# read high with the lid open which appears to be correct if I'm reading the datasheet for the Hall sensor correctly.

Wait a minute LID_CLOSE1# and LID_CLOSE2# - both signals must be active low and you said "read high with the lid open". That's it! Bring back both signals low at the Hall sensor and check eDP_BLCTRL_CPU line voltage (pin 5 at RN5257). I believe it will go high and Hall sensor as I suspected is the problem here.

P.S. But still take the R5227 measurements values.