USB stick (FAT32) not recognised by iMac, but is okay on 2004 iBook

Macs can be very picky about the USB sticks they use. Many USB sticks are very poor quality even from respected brand names.

I've also had problems formatting a particular USB stick on one Mac and then another identical Mac won't read the USB stick. The only difference between the two Macs is the version of macOS used. The USB stick was formatted with FAT32 each time. It didn't matter whether the newer or older macOS. I could easily read and access the USB stick from a Linux system each time.

For best results format the USB stick on the older Mac. Macs are not very forgiving if some odd block size is used in the formatting. It is possible the older OS on the iBook isn't able to read some new variation in the FAT32 format.

Well it would be interesting to see how the QU mixer has formatted the disk, on your iBook plug the stick in

and highlight it and press Command-i to get the info panel up, look in the General section.

When you plug it into your 2013 iMac do you get an error message that pops up?

Have you tried Disk Utility to format it.

Open Applications/ Utilities/ Disk Utility elect the USB disk on the right, press Erase

give the Disk a name, next to Format select MS-DOS(FAT) and next to Scheme select Master Boot Record.

click on. the Erase button, now try and see if the Audio mixer can see the newly formatted USB.

Have you contacted the Audio Mixer manufacturer to ask them if the formatting they use can be used on Mac OS X Mavericks.

Perhaps you might be able to mount it using Terminal.

On the iMac 2013 plug in the USB

Open Terminal, it is in the Applications/ Utilities folder.

Enter the text

diskutil list press return

Terminal will list all disks on or attached to the Mac

look for the usb and note it's identifier.

for example on my Mac there is a FAT32 USB attached, it is an internet dongle its Identifier is disk6s2, see below.

your USB disk will have an identifier similar but will probably have a different number,

back to Terminal and enter the text,

diskutil mount disk?s? (please exchange the ?'s for the numbers for your USB) press Return

hopefully this will mount your USB, there are no guarantees.

Try formatting a spare USB as MS-DOS FAT on A Master Boot Record as described earlier

do it on the 2013 Mac and see if your Audio mixer can see it and save it's settings to the USB.

When you used the diskutil mount command in terminal did you input the correct identifier for your USB.

you can see for the screenshot above that the Identifier for my Internet dongle volume is disk6s1

so I would type in

diskutil mount disk6s1 and then press Return

Terminal should give you a response to the command

Can you try it again and maybe share a screenshot.