820-00165a Spillage around Y1915 and u7701

TBFix

Member
Board was powering up intermittent with black screen (chime) so replaced U7701 and Backlight was ok so began installation of Os.
After reboot it wouldnt turn on again so found some corrosion around Y1915. Replaced both resistors and board still powering intermittent.
Board stopped turning on the only drawing 250ma black screen no chime but usb boot hdd has activity (Blink a couple of times).
All rails have correct voltages except for backlight (PPVIN_S0SW_LCDBKLT_FET) .

PPbus has 8.58v
U1950 PM_PCH_SYS_PWROK 3.43v
Reflowed SMC then reballed but still same.
Any point in relacing Smc or what am I missing?.
 

2informaticos

Administrator
Staff member
So board works, only missing backlight?
PRAM reset tried (2-3 times)?
Caps lock reacts, chime, external video?

Did you check XW7720 bridge?
 

TBFix

Member
Hi No external video ,no chime, Usb activity on usb 3.0 hdd nothing on keyboard or mouse. Also how to check XW7720?.
. Current jump to a little over 300ma the immediately back to 250ma. Tried Pram reset with internal keyboard but it didnt respond.
 

2informaticos

Administrator
Staff member
Looks like board doesn't really boot.
So no backlight issue, probably.
Very strange to get USB activity in this case...

Do you have oscillation on Y1915?
Also check PCH_CLK32K_RTCX1 at U1900 output.
 

TBFix

Member
It originally booted but with no backlight but took a few presses of powerbutton and after I removed it from case and placed on bench it then started to boot. I replaced the Backllight Ic and had picture chime etc and began install os . Strangely the wifi acted strange and wouldnt connect during setup so rebooted it and thats when I get this status now.
 

2informaticos

Administrator
Staff member
PCH_CLK32K_RTCX1 should be stable 32KHz, square wave.
Did you test the board alone on the desk again?
Try disconnecting LIO flex and airport card.
 

TBFix

Member
I changed the probe now getting 32.hkz wave, everythign is dosconnected inc Lio cable but still same and 24mhz at Y1915
 

TBFix

Member
Yes stable on all 3 pins

PLT_RESET_L seems to be pulsing between 40mv to 160mv
 
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2informaticos

Administrator
Staff member
Check if you get al voltages at pages 57/58.
If yes, then should be PCH issue.
Heat it with quality flix.
No more than 180-200 degress, just to burn eventually accumulated crap underneath; no need to melt the balls.

Don't forget to remove SSD, airport and LIO flex for previous test.
 

TBFix

Member
Yes all Voltages on page 57/58 are present. Heated Cpu to 180c with Amtech 559 flux from Rossman store but still same . Any other ideas?
 

2informaticos

Administrator
Staff member
Should still be corrosion issue.
Check all resistors and traces around SMC.
Also inspect resistors under PCH.
No activity possible untill PCH releases PLT_RESET_L signal; nor even SPI chip is accessed.
 

TBFix

Member
Any point in replacing Smc ? .
What signals are required for PCH to release PLT_RESET_L signal ?

Also is it normal at start it stops at 20ma for a second then jumps to 260ma?.
 
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2informaticos

Administrator
Staff member
PCH needs to receive confirmation that all voltages are present, in order to release PLT_RESET_L.
Pin 3/U1950 is latest singnal expected by PCH in this sequence.
 

TBFix

Member
So probably dry joint on pch/cpu then or bad Pch

What voltage should be on PLT_RESET_L ?
After reflow Im getting 3.3v should it be 1.05v?
 
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TBFix

Member
Yes current draw just goes a little higher to 320mv.
PLT_RST_BUF_L
PCA9557D_RESET_L
SMC_LRESET_L
CAM_PCIE_RESET_L
BKLT_PLT_RST_L

Are all present and 3.3v

Where can I find a flowchart/list of the what signals/voltages should be present in correct order?.
 
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