A1706 / 820-00239 - Burn at touch bar connector. All power rails good not turning on

[2informaticos]

There should be a reason it got burnt; any history available?
No other pin affected?
Do you get VCORE?
Check voltage at all big coils; also page 78.

Test the board disconnecting J4401/02.

 

[acowan]

No history at all
All other pins checked and verified no short to ground
PPVCC_S0_CPU 1.06v at C10G1

Removed J4401 and J4402

Board responds to holding down the power button - hold it down for long enough and it will take 2mA .. press again goes back into start-up routine back to 620mA

I wonder if this is display issues

 

[2informaticos]

You must always check USB activity, before looking for video issue.

 

[acowan]

Does that apply to USB-C .... no absolutely sure how to check for USB-C activity other than basic current,violate from the USB-c meter

Managed to get a fan spin, taken board out and narrowed it down to no fan spin when tpad is connected

 

[2informaticos]

Use USB-C hub and connect a pendrive with macOS.
Must have a Link LED which can confirm USB activity if flashes.
You can test at least if get steady light on USB mouse.

 

[acowan]

USB activity confirmed on a USB - USB-C converter to an external SSD.

 

[acowan]

No history but I've found a previous repair ? .. ? Looks like Q4400 has previously been replaced and maybe some other components. Hmm I wonder if the original problem was on PP1V8_S0SW_DFR as that's connected to Q4400 and the pin next to the burn.

 

[2informaticos]

Working on the boards already touched by someone else, is always a nightmare.
You can waste your time, without any success.

 

[acowan]

Oh yes - I can see. I like the challenge though

 

[2informaticos]

If you have USB activity, is now time to test external video.

 

[acowan]

Yup .. EDP_BKLT_EN is missing and given how stupidly fiddly the display connector is i'm not hopeful but lets give it a go

 

[acowan]

PP1V8_S0SW_DFR <-- 3.8v now that's not right

Thankfully PP1V8_S0 and PP1V8_S0_PCH_VCCHDA are 1.8

 

[acowan]

U4404 1.8v voltage regulator removed .. PP1V8_S0SW_DFR is now at 0.5v. Wonder where this 0.5 is coming from ... hmmmm

 

[2informaticos]

So an overvoltage occuredd at PP1V8_S0SW_DFR.
I don't know if that could generate letal damage on touchbar circuitry.
There are few pull-up resistors on U3900 lines too; it could be also affected...

 

[acowan]

I'm sticking with this board - something to do while I lockdown.

So it seems I don't have PPVCCEDRAM_SO_CPU (0v) or PPVCCGT_S0_CPU (0v)

trying to track down why PPVCCEDRAM_SO_CPU is low

U7760 has 5v at pin 1 - PP5v_s0
pin 2, its enable PM_OPC_ZVM_L is 0v - should this be high or low? Enable are usually high but PM_OPC_ZVM_L suggests low?

Checked U7790 0v at pin 4 - PM_OPC_ZVM_L
1v at pin 6 PP1v0_s3

 

[acowan]

Any idea what CPU_ZVM_L means?
Just to confirm PPVCCEDRAM_S0_REG_F is 1v

 

[2informaticos]

I saw several boards where PPVCCGT_S0_CPU only appears under graphics load, like playing YouTube videos.

I don't have any similar board with PPVCCEDRAM_SO_CPU for test.
Compare with working board, if possible.
CPU_ZVM_L is supposed to be 1V and U7790 translate it to 3V at PM_OPC_ZVM_L output.
Same circuit exists on 00840/875 boards, check the levels there.