820-3435 .74A then .54A then OFF

[2click]

Hi, this board tries to start, goes to .74A a couple seconds and goes down to .54A and then it shuts down and repeat the same over and over again. I checked the board for corrosion and found corrosion on R6102, I cleaned it on the ultrasonic and had to change R6102 after doing that, now it is having the same behavior.
What should I check first?

Happy New Year!

 

[2informaticos]

Check ALL SPI Bus Series Termination resistors and their traces.
Clean/remove J6100.
Reball SMC, as usual for corroded boards.

Does it start in SMC bypass mode?

 

[2click]

I reballed SMC, j6100 is clean and SPI Bus Series resistors have correct values and look OK. Still not working properly. On PIN 1 R6115 getting a pulse when turning on, but only a pulse of around 1v and then goes back to 0v.
I was thinking about reprograming BIOS, I have a TL866Plus but can´t read the BIOS on that programmer or maybe I am doing something the wrong way... Does that bios need different programming ?

 

[2informaticos]

Use new chip for U6100, just in case.

 

[2click]

I got a u6100 from donor, but still can´t read it on my TL866, is it. different from other bios chips? I put other bios and can read them with no problem, double checked the soldering pads and they were ok. Don´t know what to do anymore...

 

[2informaticos]

Your programmer may not recognize the chip properly.
Manually choose a compatibloe chip (8MB) and try to read/write it.

 

[2click]

When trying to start it in SMC bypass mode it does the same, but the backlights turns on for a couple seconds and then turns back off but this time doesnt loop, it stays off.

update: I was turning it on without the hard drive, with the hard drive it turns on, get to the login screen for around 10 seconds and shuts down... Changed the cpu thermal paste, same behavior...

 

[2informaticos]

Can you access boot menu?
Still turns off then?

 

[2click]

I can but still shuts down...

 

[2informaticos]

If turns of in boot menu, then is no macOS related issue.

Does this with original BIOS?
Clean ME region, just in case.

 

[2click]

It turns off in the boot menu, it shows me the hard drive to boot of around 10 seconds, the same that in login screen and it shuts down, the BIOS is the original and the problem is that I cant read the BIOS chip in my programmer...

 

[2click]

Ok, so I couldn´t reprogram the BIOS because I think it´s an EEPROM and don´t have programmer for that. but found out that it only starts in smc bypass mode, it loads to the log in screen and turns off 10 seconds later. Does the backlight can make the board to shut down? It is wierd that only in smc bypass mode I get backlight and image for a couple seconds, but trying to boot it normally it doesn´t turn on the backlight... what could make the board to shutdown? I checked temperature and current sensors and everything seems to be ok.

A little detail: When it turns on, it starts at 600-700ma then it goes down to 360ma and starts to go up by 10ma until it gets to 390ma that´s the point where it turns off. When it turns off PPBUS_G3H goes as low as around 7.8v. I dont think that is normal behavior...

 

[piernov]

Did you check charging circuit current paths sensing and fuse?

 

[2informaticos]

Shouldn't be a sensor issue, if still turns off in SMC bypass.
Looks like a problem near U7100, causing PPBUS_G3H drop.
Inspect that area, resolder and check traces.
Try changing ISL6259.
Test with fake charger, or lab PSU.