help acer v3-471g backlight problem....

[rheyntau]

hi guys....gud day ...i have an acer v3-471g
DAZQSAMB6E0 REV E model ZQSA
the problem is after 5 to 10 mins the backligt is off but i can see the display/graphics with a flashlight...

i already try other lcd and it has same probmem......


can anyone help me.....

thanks in advance...

[mon2]

Re: help acer v3-471g backlight problem....

Hi. Can you post the schematic? Or link it if it is on this forum.

[mon2]

Re: help acer v3-471g backlight problem....

I think I have the schematic for this logic board.

Update - referenced the wrong schematic earlier from the database.

measure the voltage on pin # 26 (BL_ON) of the CN1 connector:

a) when the backlight is ON

b) when the backlight is OFF

[rheyntau]

Re: help acer v3-471g backlight problem....

this is the schem....

[rheyntau]

Re: help acer v3-471g backlight problem....

I think I have the schematic for this logic board.

Update - referenced the wrong schematic earlier from the database.

measure the voltage on pin # 26 (BL_ON) of the CN1 connector:

a) when the backlight is ON

b) when the backlight is OFF

i test the voltage on bl_0n whenthe backlight is on 3.2v and when it off after 5 mins.... 0.5v.....

[mon2]

Re: help acer v3-471g backlight problem....

How do you get the backlight to turn on again? Power cycle the unit?

What is the history of the unit? Liquid damage?

Perhaps a lid sensor fault and the logic board thinks the lid is closed.

Can you turn off all power savings mode?

What if you enter the bios setup screen and leave it on this screen? Will the display backlight remain on ? Test the idea. Leave it on in bios mode for 15-30 mins.

[rheyntau]

Re: help acer v3-471g backlight problem....

How do you get the backlight to turn on again? Power cycle the unit?

What is the history of the unit? Liquid damage?

Perhaps a lid sensor fault and the logic board thinks the lid is closed.

Can you turn off all power savings mode?

What if you enter the bios setup screen and leave it on this screen? Will the display backlight remain on ? Test the idea. Leave it on in bios mode for 15-30 mins.

itry to turn on and off...its dsame if i turn it off for how many hour and if i open it again the backlyts on and after 5 mins it off and if i torn ooff it again and on it again the backlyt is off even ot boot...

i try to injected 3v on bl on and the backlyt on...

[rheyntau]

Re: help acer v3-471g backlight problem....

update i try to remove Q2 and test it now it has a backlyt ...d Q2 marking code is K72 F.....i have a scrap board and the transistor code is K72 X1 ist d same?

[mon2]

Re: help acer v3-471g backlight problem....

What is the voltage on pin #2 of Q1 mosfet ?
Voltage on pin #2 of Q3 ?

To check if a mosfet is damaged, remove all power.

Meter in resistance mode (2k scale).

Check the resistance between:

Source and drain
Source and gate
Gate and drain

Of each mosfet Q1 and Q2.

Q2 may be ok. If you remove Q2, backlight will work since the default pull up voltage of ~3v will appear on the BL_ON pin due to pull up resistor @ R40.

First need to confirm if any of the mosfet driver parts are being turned off for this signal line.

Post your voltage readings.

[rheyntau]

Re: help acer v3-471g backlight problem....

thank you so much for the help and advice..i replace Q2 and now its fine ....

[KleeMapple]

Re: help acer v3-471g backlight problem....

hi guys newbie here can u gave me a pic were Q2 located on board DAZQSAMB6E0 REV.E MODEL :ZQSA . I got a same problem like yours sir .

[mon2]

Re: help acer v3-471g backlight problem....

Hi. Personally have never seen the board and do not see a boardview file in my database.

Review the connector for the LCD display. This backlight circuit featuring Q2 should be nearby. The mosfet is very common and is a SOT23 package (3 legs) = 2N7002.

See attached as a reference for the component shape. Do not worry about the topside markings as your logic board may be fitted with a different version of the same part (many vendors build this part).

Post clear pics of the LCD connector and nearby parts for a review. About to enter my beauty sleep mode after a bit of Aliexpress shopping...

[SMDFlea]

Re: help acer v3-471g backlight problem....

ZQSA Rev F boardview https://www.badcaps.net/forum/showthread.php?t=50906

[mon2]

Re: help acer v3-471g backlight problem....

Thanks @SMDFlea.

See attached.

[KleeMapple]

Re: help acer v3-471g backlight problem....

Thnx.^^ guys i know where to look now.btw can i ask? i had old laptop that has q5 to q36 or bunch of it.can i used it to replaced dmg Q1 o Q2?

[KleeMapple]

Re: help acer v3-471g backlight problem....

Or should i chck its volts?

[mon2]

Re: help acer v3-471g backlight problem....

On the laptop that is not working, measure the voltage to ground of each pin of Q2.

Meter in dc volts, 50 volts or higher scale. Backlight is usually a higher voltage of 25-50 volts.

Red meter probe to point to test.

Black probe to ground.

Post each measurement.