MacBook Pro prohibitory sign will only boot from External drive

RGLA00 wrote:

THANKS. Already tried that. As stated - upgraded OS to Catalina.

It seems like something was corrupted as it was working fine.

Did you replace the SATA cable as recommneded when you upgraded to the SSD— it is a known weak link.

SATA replacement 13"MBP mid 2012

https://eshop.macsales.com/item/Apple/8211480/%20%2013%22%20MacBook%20Pro%20SATA

If it boots externally but not internally, you can expect this cable has a fault.

RGLA00 wrote:

I didn't do that yet. It it's recognized by DU and other programs it seems like that would rule out a bad cable. I'll try and put it in an external enclosure to see if that works. thank you

SATA cables are flexible circuit boards, usually mylar, with printed circuit traces taking the place of wires.

In the case of an intermittent generic failure, the electrical continuity of a cracked trace on both sides of the crack is very often a function of the temperature of the unit at the point where the crack exists.

As a unit heats up, it expands, and as it expands, the crack widens, eventually forcing a complete electrical separation to exist on both sides of the crack, hence a failure. As it cools down, electrical contact may once again be restored.

RGLA00 wrote:

Hi. I've tried a lot of things but here's what's going on.

I have a mid 2012 MacBook Pro running High Sierra with a newish SSD - less than 2 years old. Was working fine then stuck. On reboot I got the prohibitory sign.

I got into recovery mode and ran disk utility. It said there was a problem with a TM snapshot. I tried to get to terminal to delete per info on internet but I couldn't.

I decided to update to Catalina to see if that would help. It got the computer to boot up and I was able to get most of my data off. But when I rebooted it was back to the prohibitory sign.

It seems like the Internal SSD keeps getting unmounted/disabled but when I click on it in DU it says it's fine.

Apple Hardware diagnostics states everything is fine.

I made an external boot drive (or so I thought) I think I made a clone of my drive somehow. This allowed me to boot up the computer. I made a time machine back up manually and by the next morning the computer seemed to be fine but that only lasted a day.

Now when I boot from from the external (clone?) sometimes it boots to my old wallpaper and sometimes it boots to Catalina default. Even with my old wallpaper I'm running Catalina on the boot drive and not HS.

It seems like the internal HD got messed up by TM and now won't work. But there was 2 days when it worked fine with. Now I can only boot from external but DU says internal is okay and mounted. Does that rule out the sata cable? Could an SSD drive fail this quickly.

<ENTRECHECK.log>

If your Mac starts up to a circle with a line through it

https://support.apple.com/en-us/HT210901