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820-2915 gMux Firmware updated but no blacklight now

R

RaezorSharp

Member
Hi,
I received a 820-2915 15" 2011 board that had the gMux hardwired to bypass the external AMD chip and was asked to do the gMux firmware update that allows brightness control. Upon removing the several wires that are involved in the bypass, I was able to reprogram the gMux using DosDude's firmware update but now the display is not showing a backlight.

Looked at BKL_PWM fail and I've checked R9704 is 33ohms, R9693 is 100k ohms, C9704 is not shorted to ground.

Also checked Pin 2 on U9701 (LP8550) that enable is 3.3V

BKL_PWM is only 8.8 mV, so I hard wired BKL_PWM to 3.3V and still no backlight

Also checked Output on PPVOUT_S0_LCDBKLT is only set to 12.5v,

I've reballed U9701 hoping to resolve some poor connection on the pads but no difference, should I assume the Backlight IC is toast?
 
2informaticos

2informaticos

Administrator
Staff member
Post diode mode to ground on return lines; be sure all resistors are good.

Do you have now both BKL_EN/PWM with 3V?
Did you try PRAM reset (2-3 times)?

Did you try another (compatible) LCD assembly?

U9701 gets 3V3 and 5V?
Check if D9701 is not shorted.
 
R

RaezorSharp

Member
Tried the PRAM reset 3 times - No change
Swapped LCD with anther - No change
Both BKL_EN/PWM are now 3V (remember I have wired BKL_PWM high with a wire, is was only 8.8 mV)
Checks all the LCD return line resistors that are basically wires (0 ohms) - No issue
Diode mode R9717 = 627, R9718 = 628, R9719 = 628, R9720 = 626, R9721 = 626, R9722 = 625
U9701 has 5V for VIN and 3.3V for VDDIO (measured off C9711)
D9701 was not shorted.
 
R

RaezorSharp

Member
Replaced U9701, no issue with A5 to K/D9701.

Had to have hard wired BKL_PWM to 3.3V to see any video. So I can see some video now but on boot-up I see some lines on apple logo when it starts and video is shaking, background goes to total 'Red' when I shutdown computer.
 
2informaticos

2informaticos

Administrator
Staff member
"Had to have hard wired BKL_PWM to 3.3V to see any video"
You already had 3V there, in a previous post
"Both BKL_EN/PWM are now 3V"

Is dificil to help if we cannot trust provided information...
Where did you get the actual 3V for BKL_PWM?
 
R

RaezorSharp

Member
In the previous post I still had BKL_PWM hardwired as indicated on the previous message, guess I should have mentioned it was still hardwired.

Took voltage 3.3 volts from the JTAG connector J9600 Pin 1. Also previously checked that R9704 Pin 1 was connected to R9693 Pin 1 as I didn't understand why U9600 was not providing 3.3 volts.
 
2informaticos

2informaticos

Administrator
Staff member
So you don't get backlight if join BKL_EN/PWM?

"background goes to total 'Red' when I shutdown computer"
Do you mean the screen stays red when machine is off???
 
R

RaezorSharp

Member
I have not tried to tie both BKL_EN and BKL_PWM together as I just thought it was quicker to take 3.3v from JTAG connector.

As I shutdown the MacOS the screen goes into some weird 'Red' colour as I'm shutting it down. Screen then goes black when the computer is off.
Video seems to have a significant sync type issue.
 
R

RaezorSharp

Member
So is the recommendation to tie the BKL_EN to supply power to BKL_PWM? Do you believe this will resolve the video shake issue?
 
2informaticos

2informaticos

Administrator
Staff member
Didn't try yet???
Backlight must appear AFTER image is enabled, and should go off BEFORE image dissapears.
Just to avoid any artifacts on the screen...
 
R

RaezorSharp

Member
Well apparently BKL_EN is not providing 3V.....Not sure what I was checked before but apparently not the correct thing.

BKL_EN is only in the mV's.....since I bridged BKL_PWM to BKL_EN the display is no longer visible since Backlight is not enabled.
 
R

RaezorSharp

Member
Ok with NO bridges...

BKL_EN - 140 mV
BKL_PWM - 1 mV

R9703 - 33 ohm
C9704 - 458 diode mode reading
R9731 - 176k
R9715 - 97k

R9666 - 4.7k
 
R

RaezorSharp

Member
I just switched R9666 to the correct resistor, noticed it was incorrect.
Not sure why BKL_EN was 3V before, might have been my error.
Yes, LCD was connected and LCD works.
 
R

RaezorSharp

Member
No not solved, I only indicated that the LCD was connected and it works....initial issue has not been resolved.

I'm going to have to go back to the start on this and check the path, not sure what is happening with BKL_EN and BKL_PWM.
 
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