Acer M5-481PT backlight issue

[p1muserfan]

I have a backlight issue with a known good screen, video is fine on external, can see internal image on screen with flashlight. Think issue is with backlight control (p. 15 of schematic). I have voltage (3.3V) with machine running on pins 2 and 3, need voltage at pin 5 to have backlight, correct? Need to learn to interpret a schematic...

[dj_ricoh]

Re: Acer M5-481PT backlight issue

List all the pins voltage.
This is the start

[p1muserfan]

Re: Acer M5-481PT backlight issue

List all the pins voltage.
This is the start

Only have voltage (3.3) on pins 2 and 3, everything else 0.

[dj_ricoh]

Re: Acer M5-481PT backlight issue

Find u22 and list the voltage from there.

Aparantly this machine got led ic driver. Similar with those crap mac's

[dj_ricoh]

Re: Acer M5-481PT backlight issue

And find u2 to
Get the voltage from there to

[p1muserfan]

Re: Acer M5-481PT backlight issue

Find u22 and list the voltage from there.

Aparantly this machine got led ic driver. Similar with those crap mac's

Have 19v at pins 16 and 19,nothing at 2,5, or 14

[p1muserfan]

Re: Acer M5-481PT backlight issue

And find u2 to
Get the voltage from there to

Have 3V at 1,3,4 and 6. Good chip

[dj_ricoh]

Re: Acer M5-481PT backlight issue

Go to kbc and find bl_on from pin 2.

See if its 0 to. Lift that resistor and check on pad if its 0 before u22 input.

The thing is this u22 its interconnected with kbc and we need to find out who is bad u22 or kbc fir not enabling the back light

[dj_ricoh]

Re: Acer M5-481PT backlight issue

Check for short with ground

[p1muserfan]

Re: Acer M5-481PT backlight issue

Go to kbc and find bl_on from pin 2.

See if its 0 to. Lift that resistor and check on pad if its 0 before u22 input.

The thing is this u22 its interconnected with kbc and we need to find out who is bad u22 or kbc fir not enabling the back light

BL_ON from pin 2 of U22 ties in to the backlight control circuit of Q16 (I searched the entire schematic and those were the only places that BL_ON was found) thru diode D8 to LID#. LID# also comes from the hall sensor and ties in. LID# then goes to pin 93 of the KBC, where I measured 3.3v. So KBC is ok? U22 no good?

[dj_ricoh]

Re: Acer M5-481PT backlight issue

Logical yes.
I'm thinking if its ok to give power without u22.

If you lift it up does the voltage come back?

[dj_ricoh]

Re: Acer M5-481PT backlight issue

Just take u22 out and check for short with ground on each pins.

If there is no short check u22 if its got short on pins via ground pin.
Don't apply power its much safer this way.

[p1muserfan]

Re: Acer M5-481PT backlight issue

Just take u22 out and check for short with ground on each pins.

If there is no short check u22 if its got short on pins via ground pin.
Don't apply power its much safer this way.

Removed U22 from board and pin 2 and all other pins that need/supply voltage on chip pad are not shorted to ground. Suspect bad chip. Have ordered one and will report back when it's replaced

[dj_ricoh]

Re: Acer M5-481PT backlight issue

Nice.
I hope it works out.
From china?

[p1muserfan]

Re: Acer M5-481PT backlight issue

Nice.
I hope it works out.
From china?

Mouser Electronics, Mansfield Texas, about 1/2 hour from where I live. Awesome place

[p1muserfan]

Re: Acer M5-481PT backlight issue

Changing U22 didn't help. It's now time to consider this motherboard isn't the right one for the screen. This board is not the one that came with the computer when I bought it almost a year ago. The original has a dead short which is gonna need to be fixed. Both boards have identical part #s and revision numbers but as you can tell by the pictures, they're different. The original doesn't have the U22 chip that I just changed, although the schematic matches the "new" board perfectly. The screen lit up fine with the original board before it died. Is that why this board will not light up the screen?

[p1muserfan]

Re: Acer M5-481PT backlight issue

Forgot pictures in previous post again

[dj_ricoh]

Re: Acer M5-481PT backlight issue

what voltage you got on Q16?
that zone its super hot.

something missing there it does not trigger the BL.

check all resistor and diodes.
you even got a transistor hooked to ground with feedback. Jesus
Let`s focus there.

on your second board find the big coils and see where is shorted.
prepare your lab PSU and will lift it up

[p1muserfan]

Re: Acer M5-481PT backlight issue

what voltage you got on Q16?
that zone its super hot.

something missing there it does not trigger the BL.

check all resistor and diodes.
you even got a transistor hooked to ground with feedback. Jesus
Let`s focus there.

on your second board find the big coils and see where is shorted.
prepare your lab PSU and will lift it up

Q16-3.3v on pins 2&3, nothing anywhere else. However only have 3v on one side of R296. Will steal from other board and report back

[dj_ricoh]

Re: Acer M5-481PT backlight issue

Q16-3.3v on pins 2&3, nothing anywhere else. However only have 3v on one side of R296. Will steal from other board and report back

Don't install the resistor aftet you took it out check to see if its not shorted to ground.
Maybe something else made the resistor go bad.

Check everything link to ground.