820-3115-B No Backlight

[mushr00m]

Found bad F9700 and replace it with another one

Now I do get 11.06V

But still same behavior the machine turn on but still with a backlight issue.

If I use a flash light I can see the user screen to login

 

[2informaticos]

Any history available?

Check for corrosion between U9701 balls.

BKL_EN/PWM both come high?

 

[mushr00m]

No history available.

BKL_EN = 2.7V
BKL_PWM = 0V

 

[2informaticos]

Remove R9704 and run wire from C9704 to R9715.
If get backlight, do PRAM reset 2-3 times and rebuild original circuit.

 

[mushr00m]

I did it

No backlight.

However I still tried to do PRAM and couldn't.. WEIRD

OPTION + CMD + P + R

Also I removed and reballed again just in case it has corrosion under U9701

After doing everything I am testing it with the battery!!

Still image appears with a flashlight.

Should I use charger instead? To do PRAM same thing?


What's next

 

[2informaticos]

Don't bother with PRAM reset, if no backlight forcing BKL_PWM signal.

Check all resistors around U9701.

Compare diode mode readings with attached notes.

 

[mushr00m]

Should I put back R9704 to measure everything?

About comparing diode mode readings with the notes. I am not sure about the notes since it mentions things like

FB A5 656

I guess 656 its the diode number but how about FB and A5

All the resistors around U9701 are matching schematic ohms numbers.

Just give me a hint on to compare diode with your attached numbers and I will finish it in a minute

 

[mushr00m]

FB A5 - 656 0
SW_x B1/B2 - 404 405
FILTER C2 - 568 536 NOT SURE IF ITS THE PIN BKL_FLTR
VSYNC D2 - 568 535
ISET B3 - 570 537
FSET B4 - 572 539
SCL D3 - 439 415
SDA D4 - 443 399
EN A3 - 570 540
PWM A4 - 535 503
OUT1 E5 - 658
OUT2 D5 - 659
OUT3 C5 - 659
OUT4 E3 - 656
OUT5 E2 - 656
OUT6 E1 - 656

These are my measurements right besides each of your diode readings I was following END OF LINE NAME

First example would be FB = PPVOUT_SW_LCDBKLT_FB right? and this one is 0

Actually OUT1 I am not sure, is it BKL_ISEN1?? If so why call it OUT if its called ISEN??

 

[2informaticos]

"FB = PPVOUT_SW_LCDBKLT_FB right? and this one is 0"
Do you mean 0 (short), or OL (open)?
Please, post accurate information.
OL can mean broken trace, depends on which point you've checked it.

You should check XW9720 bridge continuity.

 

[mushr00m]

Yes its 0 short!

Just confirmed again

Actually found C9797 in short removed and the short is gone.

Can I assemble and use the board without it?

 

[2informaticos]

Should be good to solder another in place.

 

[mushr00m]

So I removed C9797 and replaced it with another one. Short is GONE =)

However still no backlight

Comparing diode mode

FB A5 - 656 MINE IS 559

Could it be a bad U9701?

 

[2informaticos]

No volt at all at backlight output?
Check with LCD connected.

You may need to change U9701.

 

[mushr00m]

PPVOUT_SW_LCDBKLT_FB = 2V

Should I replace U9701?

Some questions that STILL not answered and I still curious about it

Without C9797 would it work normally?
Is it ok to test and turn on all the times using only the battery?

 

[2informaticos]

Can test without C9797, but is recommended to solder it for long term use.

No problem to test with battery alone (without charger).

 

[mushr00m]

OHHHHH THANK YOU VERY MUCH FOR ANSWERING OLD QUESTIONS.

HOWEVER YOU FORGET TO TELL ME WHAT DO NEXT!!!!

LET ME REPEAT AGAIN TO YOU!!!


PPVOUT_SW_LCDBKLT_FB = 2V!!!!!!!

Should I replace U9701??????????????????

OR WHAT SHOULD I DO???????????

 

[2informaticos]

Yes, is strongly recommended...

 

[mushr00m]

Replaced U9701 with a 100% working one from a 2936 machine and still didn't work.

What's next

 

[2informaticos]

Check continuity between K/D9701 and A5/U9701.

Post Q9706 voltages.

 

[mushr00m]

Theres is continuity between D9701 and A5 U9701

I measured Q9706 only the bare board without the screen connect

Q9706
PIN3 = 12.19
PIN4 = 12.56


All the others PINs looks like starts with 0.300v and drops to 0V