Time Machine question

[Mac Man 2007]

I was having trouble reinstalling Mojave even after wiping my flash drive clean on my 2013 Mac Air. The Genius Bar thought it was a software issue. It kept getting stuck and sitting there. Then when they tried to fix it they said it was a Flash Drive failure. I put in a new Other World Computer flash drive Aura Pro x2 and it worked like a dream. One little glitch setting it up but OWC tech phone service told me what to do (which I now forgot what is was) and if fixed it immediately.
I'd also recommend their batteries. I had a very premature failure of an SMC battery that supposedly makes them for Apple. Got around 75 cycles and it really was acting loopy. I bought a new battery from OWC and it is 97% at 122 cycles and is just about as good as the original battery that came with it new from Apple.

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[TurboSteve]

I suspect another hard drive would cure it, but i would probably put the money towards a new computer.

Today's update: Everything has failed to produce results thus far. I recently purchased a Thunderbolt cable to connect it to the iMac i'm using. I booted it to target disk mode and applied first aid and tried to restore and erase the disk, but it won't unmount. I've gotten -69877 and -69888 error codes.

This was kind of my last hope. I've read about using Terminal and entering some commands in, but i don't wan't to make the mistake of doing it to the functioning iMac.

 

[TurboSteve]

Hmmm.

 

[MacInWin]

Sometimes users experienced the time machine backup failure. Here are 4 methods to fix the time machine backup failure issue:

1. Check the file system of the external hard drive
2. Check the free storage of the external hard drive
3. Uninstall App Cleaner & Uninstaller
4. Check if other process or services are blocking time machine from running

Further, you can also check the below link for more details in regards to recovering data from the affected time machine:
How to resolve No Time Machine Backup Found Issue

Hope this will help!

@andystuart77, you have posted that same post twice, and it doesn't work. As i have been saying, I've reformatted the target external drive, tried just about every trick in the book for fixing it and none of what you suggest makes any difference. And App Cleaner has zero to do with the issue. Please stop posting bad advice.