a1425 retina

[guruji]

hi all
i have a retina board 820-3462-a a1425 no power. after changing the smc the machine was restored and all worked fine with catalina 10.15.3.the after 4 days the customer gave back and it was 3 beeps ram error.So i changed all 16pcs of micron ram with same part no still 3 beeps finally i landed up chaning the bios and bingo i got display but the ssd could not boot, but i am able to boot my catalina pemdrive installation and see the ssd. so i cleaned the ME engine still same problem tried various efi/bios.next day i had a similar machine all working so i checked the ssd in the working machine and it booted well.
I copied the bios from a working machine which boots the ssd ,and guess what the same ram beep. WTF...... now i dont know is it the hardware or is it the firmware.but i noticed the firmware that works give the display white and the firmware with the ram error used to give me black screen with white apple logo.i have checked all pch memory straps.
has anyone faced this

[piernov]

Re: a1425 retina

Older BootROM versions cannot boot from APFS.
macOS High Sierra or newer must be reinstalled on the internal drive to get the BootROM update and be able to boot APFS filesystems (default for SSD since macOS High Sierra).
In any case if it is beeping there is probably still a problem with RAM circuit or CPU.

[guruji]

Re: a1425 retina

Hi Piernov
Thanks for your reply
That what I thought it is a Ram problem.but when I put another efi it takes os upto 10.12 the moment I try installing 10.13 it gave me
An error cannot determine firmware and if I force to install the next reboot I get ram beeps previously the machine worked on Catalina some firmware update messed it up I am posting the efi version before and after.I notice too many invalid entries in the VSS store when I strip it in UEFI tool