820-3330 missing bkl_pwm

[shanenin]

I have a missing backlight and 0v on bkl_pwm. I am able to get the backlight to come on if I jump pp3v3_s0 to bkl_pwm. Any ideas to why bkl_pwm is 0v?

I get 30 volts on the main backlight line without the jumper

 

[2informaticos]

Normal voltage is 39V there.
Do PRAM reset and comment.

 

[shanenin]

I tried to do a pram reset and it did not chime. I then replaced the backlight driver. Now my backlight output is down to 12.* . I am guessing my solder job may be bad. It seemed to go perfectly

 

[shanenin]

changed the backlight driver and I am back up to 27.8v. Since the speakers are connected to the board on this model, I should be hearing it chime when resetting the pram(but it did not)? I did hear it chime originally when first looking at the computer before removing the logic board

 

[shanenin]

I do get usb light and when resetting the pram it goes off. Is it normal when a logic board with the speakers attached to it, removed from the case, not to chime?

 

[2informaticos]

You must keep pressing the PRAM reset keys until USB mouse light comes on again.
In fact you are using its light instead of chime.

 

[shanenin]

I held the keys and reset the pram several times in a row, it flashed multiple times. I was just asking about hearing the chime if the logic board is pulled out as a second quesiton

 

[shanenin]

it is working now. Not sure what happened. it is working with 31.5 volts on backlight out. Is that seem like an issue since it is not 39v?

 

[2informaticos]

I only saw this problem on machines with EFI password.
The last one 3 days ago...

 

[shanenin]

what about it working and it is only giving 31.5 volts on the backlight output? Should I be concerned?

 

[2informaticos]

I doubt you can get backlight with less than 34V.
Be sure to measure correctly.

 

[shanenin]

Thanks for the help