My macbook turns on but will be stuck on loading screen if boot internally, after smc reset it boots fine into os but if restarted or shut down, wont boot (stuck on loading screen) without smc or nvram reset, once reset the smc or sometime nvram it boots fine into os. it boot perfectly fine if hard drive connected externally through usb without any problems. “problem is definitely not related to hard drive or macos” hard drive been replaced twice, hdd flex cable also been replaced, os been reinstalled freshly many times. i know its an old machine not worth wasting time or money but i might want to do it as a fun project so any help or suggestions what could be the possible component behind it ? it has been previously repair few years ago for no power (was completely dead) not sure what component has been replace.
Macbook pro Mid 2009, A1278
Macbook pro Mid 2009, A1278