Macbook Air 2015 Booting Very Slow and Stuck on apple Logo 99%

[platinumsteel]

Hi guys i have my personal MacBook Pro 2015 820-00165 board that was working fine for more than a year and one day stopped working on my original Magsafe charger. It was turning on with my bench power supply. Opened it up and while diagnosing that somehow i ended up with a shorted smc.The line which was shorted was SMC_PM_G2_EN. I removed the SMC and short was gone. So all I had was another working donor board 820-3435 which i used to program it's SMC to 820-00165 using the SMCTOOL By MuertoGB.Took that SMC and use it on my 820-00165 board .And my board started working again. PPBUS_G3H 8.56V. But started this extremely slow boot up. It will take 2 mins to hear the chime. Then another 2mins to show the apple logo and then it will take about 5 mins loading the OS .. then will get stuck on 99% and would get stuck there permanently.. So i tried like 3x different cleaned Me Region Dumps for this board from badcaps bios section. I tried different and older MacOS versions. Tried 5 different original SSD's . Also tried booting from a MacOS USB same issue. Used a known working chassis with working keyboard and trackpad and battery. plugged and unplugged,. Tested all resistors around the SPI and U1900 Area . Had 1 shorted cap just above U1900 and a Open Line Resistor. Changed them out and replaced them according to the Schematic. But nothing changed. Still boots extremely slow. Was wondering if any of u guys have experience with this issue and can maybe guide me on a few things to check before I give up on this board. Or is it just maybe a plain bad SMC. Or maybe I should of used a 820-3437 SMC as was recommended for use with 820-00165 boards with SMCTool.?Any help will be greatly appreciated thanks.

[livfe]

I have exactly the same problem, does anyone know the solution?

[kevingill]

As I understand it, as long as the Mac boots, a slow boot is caused by a bad SPI ROM. There are some bad dumps on here, so I'd try a few others first.

[reformatt]

Throttling on MAC's can be many things. They run slow with a flat battery (or missing SMBUS data to the battery), any sensor data that is missing (trackpad is the most common, but there are others on the board for voltage, current or temperature). Even had a bad Apple SSD cause it once. If you are using a donor BIOS, it must have a clean ME (i.e. the ME firmware contained in the BIOS is not initialised to an existing system). Note that Apple used a customised ME firmware compared to the vanilla Intel F/W, so you must use ME F/W specifically for each MAC system when creating a clean ME BIOS using FIT or Muerto's MacEfiTool.