820-01700 no backlight + other issues

[nininunz]

Ok so this board has been thru hell :/
Had water damage. Fixed water damage and it worked perfectly. Was putting back in top case and there was a bee in my room and I kinda maybe might have thrown the board at the bee and surprisingly everything still worked perfectly except the backlight. I bought a BY-3200 cable so I could test voltages and such outside of the top case and this was my first time using it. I plugged it in, checked a few rails, then was looking at the board view on my laptop when I heard a pop and saw the magic smoke. I have no idea where it came from. Nothing was warm and no components look damaged. It was in this general area though. And like I said it looks like hell lmao I was a lil bit drunk cuz it was pissing me off. It's a personal board, not a customer one. I'm not that unprofessional. I feel like I need to figure out what went poof before I figure out the backlight problem but honestly idk what to do as I don't see anything visible. But it came from the general area I was probing with the backlight components.

 

[2informaticos]

You must check F8400 first.
If burnt, check for short on several points of backlight circuitry.

Be aware, 3V3_G3H_RTC power supply is very close.
Leakage from backlight output can kill the board.
Board still works, only missing backlight?

 

[nininunz]

If burnt, check for short on several points of backlight circuitry.

nope not burnt. but damn I totally molested this board :/
I think I may have actually put D8410 on backwards. Can you confirm? Also note L8450 and C8463 are off the board. Neither should be crucial for display backlight though. I think. Since I'm not putting a load on C8463 just probing display pins.

Edit: forgot to say I haven't put the board back in the top case and tested if it boots since the magic smoke

 

[2informaticos]

You can't test the backlight circuit without connecting the internal LCD!

"I may have actually put D8410 on backwards."
Yeah, unfortunately; check if still good.

 

[nininunz]

I wouldn't get voltage on the display backlight pins without being connected?

 

[nininunz]

Ok so I hook it all up and it fucking worked. All this time it was just that diode =/
Aaaaaaaaaaaaaaaahhhhhhhh I'm literally crying lmfao

 

[nininunz]

Weird update. Noticed LB7000 and L3500 look kinda funky. Shown is LB7000, L3500 is not as bad. Any idea what would cause this? Good to just replace or is something else the root cause and gonna make it happen again? They're both USBC related. Neither is near where I saw the magic smoke before though so I don't think thats what it's from.

 

[2informaticos]

No big problem if coils enclosure is damaged.
I bet the core is OK.

L3500 and LB700 provide power for USB devices connected to the machine.
Check if an USB mouse, or pendrive work properly; test the 4 ports.

 

[nininunz]

Ok well that didn't last long :/
While testing the machine the display just died on me. Power cycle brings me back to my original issue, image but no backlight. Pulled the board back out and both rows of backlight caps are short to ground. I'm still terrible at understanding schematics lol. A little help on where to check would be greatly appreciated. thx.

 

[2informaticos]

What is the exact resistance to ground (ohm scale) on backlight output?
Check with internal LCD disconnected.
Inspect J8500 for damage.

 

[nininunz]

LCD connector has no damage, looks perfect.

PPVOUT_S0_LCDBKLT is 12 ohm to ground

 

[nininunz]

Side note: wtf is XW8410? It's on the board view but not the PDF and does not even have pads on the physical board.

 

[nininunz]

Ok I'm pretty dumb. Checked all the backlight caps again and one WAS bad :/
One was also bad before when I was fixing the initial water damage though. Is there something else wrong that is potentially killing these caps? Or is it just bad luck?

 

[2informaticos]

Change any cap which looks affected by liquid, on the backlight output.

 

[nininunz]

Yeah I changed them, they're all good now. Went to test and omfg this shit making me want to punch a hole in the wall. How tf does this happen? The fucking speaker amp is foaming. WHAT THE FUCK. I'm going to go cry now

 

[2informaticos]

Oooops!
The speaker amplifiers are powered from PPBUS_G3H and have direct connection with T2.
Leakage caused by corrosion can kill T2; sometime only losing sound on speakers.

 

[nininunz]

Still no backlight. Back at this board because my A1706 is annoying the shit out of me. Basically impossible to use while charging on the left side. I fixed it twice and it worked fine for a couple days then back to the same issue. Rather than fixing it right now I'd like to just upgrade to this A2141 because I can't afford another system lmao. But here's some voltages I've gathered. Q8400 has also been replaced. Honestly I'm at a loss for what the problem is.

PP1V8_G3S - 1.8v
PPVIN_S0SW_LCDBKLT - 0.01v
PPVIN_S0SW_LCDBKLT_FET - 12.73
PPVIN_S0SW_LCDBKLT_R - 12.63v
I2C_BKLT_SCL - 5.14v
I2C_BKLT_SDA - 5.14v
PP5V_G3S - 5.14v
BKLT_SCL - 5.14v
BKLT_SDA - 5.14v
BKLT_EN_R - 0v
EDP_BKLT_EN - 0v
PPVIN_SW_LCDBKLT_SW - 0v
PP5V_G3S_BKLT_D - 5.14v
PP5V_G3S_BKLT_A - 5.15v
LCDBKLT_FET_DRV - 0v
LCDBKLT_FET_DRV_R - 0v
LCDBKLT_EN_L - 11.67
LCDBKLT_FB - 0v
BKLT_SD - 11.03

 

[2informaticos]

Do you still get image, only missing backlight?
Check if DP_INT_HPD is present.
I recommend to test with known good LCD assembly.

 

[nininunz]

I really hate this board. Plugged in to test, heard pop, killed power. Inspected and didn't see anything obvious. Plugged back in and now it's stuck at 5v 45ma. Don't think I've messed with a 5v board so not sure what to check first.

Edit: 5v on all ports
Edit 2: ok so ppbus_g3h is short to ground

 

[nininunz]

I know it's been a while but last I recall it had image just no backlight. LCD is known good.