I recently bought an SSD for my old Apple computer. I updated the system from Snow Leopard to Yosemite as some applications required a newer system.

Two weeks after I found that my FTDI chip (serial to USB converter) was faulty. Tried another, same problem. After a quick loop with an oscilloscope, the reset signal was not good… I search on the Internet and found that Apple now develops its own drivers but they are faulty :/

The workaround is following.

• Disable Apple’s driver by copy/pasting the following command in a terminal
• Reboot
• Install the driver from FTDI, which is signed in case you care about :)

sudo mv /System/Library/Extensions/IOUSBFamily.kext/Contents/PlugIns/AppleUSBFTDI.kext /System/Library/Extensions/IOUSBFamily.kext/Contents/PlugIns/AppleUSBFTDI.disabled

This article has been written about Yosemite v10.10.4 and with FTDI driver 2.3. Also, even if this should be safe, backup your files!