Acer Aspire 5734Z with no backlight, replaced by LED screen, still no backlight

[ed1973]

For the first time I repaired a 5734Z Acer Aspire laptop from which the backlight did not work, but the screen showed output.
When I connected the laptop to an external monitor, it works.

First I replaced the invertor, but the problem persisted.

Then I ordered a new LED screen, to replace the LCD B156XW01 V.2 screen.
According to the supplier the LED screen was a good replacement for the B156XW01 V.2 LCD.

I replaced the screen, removed the invertor, installed the PCB, connected everything correctly, but the problem remained the same.

I saw display output, but no backlight.

Then I measured some connection points on the PCB which came along the LED screen:

+VBL : 18.06V
EN/ADJ : 3.31V
ON/PWM: 0v
-GND = GND

I am not too familiar with the terms I mentioned above, but could it be that there was nothing wrong with the display, and that a fuse might have blown on the laptop motherboard ?

When I measured voltages on the connector (which normally goes into the invertor) which I inserted in the PCB, then from left to right I measured:

GND
GND
0V
3.31V
3.31V
18.06V
18.06V

[dycc]

Re: Acer Aspire 5734Z with no backlight, replaced by LED screen, still no backlight

ON/PWM must not be equal to ZERO . this voltage is for the brightness adjustment. use schematic to find if there is no short on this line first .

now if you find nothing disconnect that pin (on/pwm) from the connector and connect (with tin) the EN/ADJ pin and ON/PWM pin directly on the invertor PCB.

it will result a full brightness on the screen .

[ed1973]

Re: Acer Aspire 5734Z with no backlight, replaced by LED screen, still no backlight

So what you mean is that ON/PWM can be shorted to GND for example ?
First I need to find the schematic of the mobo.

If there is no short, then I can bridge EN/ADJ pin with ON/PWM ?

[ed1973]

Re: Acer Aspire 5734Z with no backlight, replaced by LED screen, still no backlight

I have sent back the LED screen to the supplier.

Now I have the current LCD with the inverter and a connector that is going into the inverter PCB with the following voltages measure on the connector:

GND
GND
0V
3.31V
3.31V
18.06V
18.06V

I removed the wire with 0V from the connector, and put back the connector into the inverter.

Then I soldered the 0V connection on the inverter PCB to one of the 3.31V lines.

When I switched the laptop on, the backlight worked for a few seconds, and then turns off.

What can I do to keep it on ?

[spidey]

Re: Acer Aspire 5734Z with no backlight, replaced by LED screen, still no backlight

ccfl or inverter.

[ed1973]

Re: Acer Aspire 5734Z with no backlight, replaced by LED screen, still no backlight

But when I replaced the LCD and inverter by a LED screen, I had the same problem.

So the problem does not seem to be the backlight or inverter. And by the way, someone said that it is not normal that you have 0V on the incoming line ON/PWM.

So it looks like the problem is not related to the inverter, and not related to the backlight.

What else could it be ?

[Claudio Silva]

Re: Acer Aspire 5734Z with no backlight, replaced by LED screen, still no backlight

Check the S/IO chip, pin BLON (Backligth on), this pin will send the signal to activate de backlight on the LDC screen.

[JoeyJoe]

Re: Acer Aspire 5734Z with no backlight, replaced by LED screen, still no backlight

I used to deal with these laptops a lot. If the laptop doesn't work on an external display, then I'm sure the GPU chip has over heated. Look up gpu reflow.

[ed1973]

Re: Acer Aspire 5734Z with no backlight, replaced by LED screen, still no backlight

The laptop is working perfectly on an external display, no problems at all.

So the problem is not GPU related.

[masud]

Re: Acer Aspire 5734Z with no backlight, replaced by LED screen, still no backlight

your +VBL : 18.06V voltage is faulty (may have not sufficient amp).try to use an universal inverter.

[ed1973]

Re: Acer Aspire 5734Z with no backlight, replaced by LED screen, still no backlight

So you conclusion is that the mainboard of the laptop, is not delivering sufficient Amp, because you think the voltage is too low ?

Also somebody mentioned that it is not correct that the motherboard is giving 0V on ON/PWM, and my conclusion is, is that because of that the inverter does not get the signal to turn on the backlight. Is that correct ?

[thezozu]

Re: Acer Aspire 5734Z with no backlight, replaced by LED screen, still no backlight

Hi there, did you try to adjust the brightness of the screen from the keyboard hot keys.. if you adjust it to max it should work since it varies the voltage sent to the pcb through the board.