820-00244 refuses to power on

[iMuhtaseb]

This A1534 was brought in for a screen and battery replacement; it had no power on issues.

After the screen and battery change up the computer refuses to power on; ammeter switches to 20V successfully but without any power draw; 0.04 amp.

I checked PPBUS it’s there 8.6V or 8.7 something like that.
PP3V3_G3H is there
PP5V_S5 is there
PP5V_S4 is missing, I checked it in diode mode and compared the numbers from FlexBV; it was 0.350 on flex while 0.180 on my board;
PM_SLP_S4_L is missing of course.

Since this is a very critical issues I replaced U7650 (5V creator) and Q7660; diode readings went up to 0.210 (still now) but now the line pulses every 5 seconds..

This is a customers' computer with important data in it and kinda hopeless here.

 

[2informaticos]

First of all, welcome to the forum!

Check all you've touched in the replacement process.
Broken trace, or knocked off components can happen.

Test the board alone, disconnecting any cable, apart of USB/power flex.
Only 5V coil pulsing now?
Check for pulse on all other coils.
Compare their diode mode readings with good board.

 

[iMuhtaseb]

Thanks! I'm happy to be here.

I've taken a look at the board for any abnormality and I couldn't find it.

5V pulses while only on USB-C power cable yes..

I totally forgot about this board that I have, I compared the diode readings on PP5V_S4 and it was 0.195; meaning this is normal.

 

[iMuhtaseb]

P5VS4_PGOOD gets high for very little 200 mv then drops..

 

[iMuhtaseb]

Noticed a line "P5VS4_EN" that's not in the schematic but it shows it's derived from PM_SLP_S5_L; I checked for PM_SLP_S5_L and it's pulsing as well.. could this be the issue source?

 

[iMuhtaseb]

Under the thermal camera it shows the CD32115B00 is at 32C.. but the device is showing 20V normally.. could it be a CD3215 issues?!

After looking at the other side of the CD3215 is where a memory module is at and next to it the camera chip and pulsing..

https://file.io/yDnXHGVtcEQz

 

[2informaticos]

Did you check other coils for pulse?
L7900/60, L7290, L800/20/50, L8130 for example?

Also check for any output short on page 50.

 

[iMuhtaseb]

L7900 there’s pulse

L7960 there’s pulse

L7290 there’s pulse

L7960 (PPVCCIO) is pulsing

L8000 1.0V (PP1V_SUS present)

L8020 1.8V (PP1V8_SUS present)

L8050 1.0V (PPVCORE_SUS_PCH)

L8130 no pulse; diode mode is 0.344 while on the known-good is 0.481

 

[iMuhtaseb]

I have checked all SMC outputs in the page 50 and found no shorts.
* I have checked all points expect for "NC" or under the chip points

 

[2informaticos]

CPU core (L7210) pulsing too?

Test if starts in SMC bypass mode.

 

[iMuhtaseb]

No pulse on L7210.

SMC bypass mode; unsuccessful

 

[2informaticos]

I still suspect mechanical damage on the board.

Still pulsing with both charger and battery connected?

 

[iMuhtaseb]

Suspecting mechanical damage is very sensible especially because the tech who worked on this board its kinda his MO.

I looked over the board again (and I will keep looking) and I found two things: bits of foam around some parts on board, that foam is under the USB-C connector on board and it's copper/gold like; IDK if its conducting or not.
And the other thing is a little teeny bit of crack on BIOS chips.. I don't know if it's a valid suspect; picture below.

Yes, pulse is there on battery only too.

 

[iMuhtaseb]

Yes it's conductive.

 

[2informaticos]

Replace BIOS chip and test again.
Flash with known good BIOS, clean ME.
If no chip available, check at least if you can read/write the original.

 

[iMuhtaseb]

Having troubles reading off of the chip; its pretty annoying to install on reader PCB. How likely this is a BIOS issue?

I've put another BIOS chip from 00045 for the differential diagnosis purposes, and it's still behaving the same.

 

[2informaticos]

Original chip has broken corner.
So is normal to suspect about its integrity.

There must be something else damaged when screen and battery have been changed.
Are you working with the board alone on the desk?

 

[iMuhtaseb]

No I have the board with other computers and stuff.

 

[iMuhtaseb]

Original chip has broken corner.
So is normal to suspect about its integrity.

Its integrity indeed in question but I would like to know if this is a suspect for such case..

 

[iMuhtaseb]

I reballed the original BIOS chip.. I noticed that exactly where the small crack is a trace for 3v3 pin.. It occurred to me to start measuring for diode mode under the chip and have an idea of the connectivity but right before I started measuring the chipped corner sadly couldn't handle anymore and fell off..
I measured anyway and 3.3v is OL under the chip there's no connectivity.. Wish I measured before it cracked off..

I really don't know if this is 100% BIOS or not..

edit: before the small chip fell off it was flapping like little a thin wire hanging in there.. so IDK if the trace was already missing. picture below