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

A

acowan

Member
First attempt at fixing a 820-00239

An immaculate board, no water damage, no hot components the only area of fault is burn at J4402 between PP5V_S0_T139 and ground

All power rails look good including PP5V_S0

With battery and J4402 disconnected at start up it's pulling 640mA then up to 720mA then falls back to 620mA -What would be normal?

No fan spin - Should this model fan spin? I have no idea
 
2informaticos

2informaticos

Administrator
Staff member
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.
 
A

acowan

Member
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
 
A

acowan

Member
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

2informaticos

Administrator
Staff member
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.
 
A

acowan

Member
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

2informaticos

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

acowan

Member
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
 
A

acowan

Member
U4404 1.8v voltage regulator removed .. PP1V8_S0SW_DFR is now at 0.5v. Wonder where this 0.5 is coming from ... hmmmm
 
2informaticos

2informaticos

Administrator
Staff member
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...
 
A

acowan

Member
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
 
2informaticos

2informaticos

Administrator
Staff member
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.
 
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