No start MacBook Pro 9,2

[Procrastinus]

I have acquired a MacBook Pro 9,2 mid 2012 (A1278) running Monterey with OCLP and in very good cosmetic condition, but with a problem – it will not start regularly. Press the power button and absolutely nothing happens most of the time. If it does decide to boot (usually after a prolonged rest!) everything runs as it should – keyboard, trackpad,camera, etc. I have run all the keyboard combinations for NVRAM et al and been through the Apple list of disconnecting various cables whilst shorting the power pads. External keyboards don't help either. I have even removed the logic board to check for liquid spill and subsequent corrosion – nothing, it is spotless. Battery usage was in the 300's last time I looked and I have tried booting with power cable only. I did notice that the battery has been replaced at some time. All to no avail. Any further ideas on poking this sulky lappy into life?

 

[Fishrrman]

The 2012 unibody MBP's had a notorious "point of failure".
That was the internal ribbon cable that connects the drive to the motherboard.

When the cable starts to wear, communication is lost between the drive and the motherboard.
When that happens, one may think that the motherboard has "gone bad", or the internal drive has failed -- but it's really just a bad connection between the drive and the board.

The cable is easy to replace -- go to ifixit.com to see the procedure and get the part number.
You could order the cable from them, or get it elsewhere.

NO PROMISES that this is your problem... it could be something else... but this is something you should be aware of.

 

[Procrastinus]

Thanks for your prompt reply.
Will be off to eBay!

 

[Procrastinus]

New cable in and fitted. Guess what - it fired up and all systems and apps worked. However after shutting down normally, this lappy has gone into sulk mode again and refuses to start. I feel it must be something simple, not temperature related, not power button related. Motherboard? But then why does it work when it wants too. Perhaps angry Artificial Intelligence?
Hair being torn out! Any further ideas?

 

[Procrastinus]

You will not believe this, but I am starting to see a pattern in my sulky laptop - it needs a good nights sleep!
So first thing most mornings, it starts fine and runs as it should (CPU temp steady at around 45C). Restart works normally, but shut it down and that is mostly it for the rest of the day!!
Has anyone seen anything like this before?