Chosen Solution
Hoping iFixIt may have some answers. I have moved from iMacs to a Mac Pro, and since I wanted Thunderbolt and keeping the same image quality as the iMac, I picked up two A1407 Thunderbolt Displays. The displays function, but each have presented their own sets of problems. I’m running the latest version Mojave, with the boot rom up to date. Display One - This is the newer of the two. It has flaky ports. When I plug a USB key in the back, it sometimes mounts. None of the ports work or they all work. I can tell if the ports are working by going into displays. If the brightness slider is there for that monitor, the ports are working, if it isn’t, no ports. My thought was the logic board? I can do without the ports on that monitor if so, but the behavior is erratic. This display old firmware and the system will not let me update it. It says the computer does not require it (tried from a MBP too) Display Two - When I purchased this, I was told it had dirt on the screen. Fair enough, easy fix. When it arrived, a closer look determined it was not on the screen, it was in the screen. I took the TBD apart and separated the display. There was fine dust on the backlight. Cleaned and re assembled, including new tape. Started up and display was clean. Worked great for a week. I just upgraded the MacPro to a 1TB Apple SSD, so I had to disconnect all peripherals. Upon re-start, I get a fast RPM spin of the fan, then it settles to about 50% speed, and will not turn down. It is awfully loud and I’ve thought about disconnecting it. This has never occurred. I cannot hear the fan at all on Display One, even at start up. This display has the latest firmware. I would be OK if I could get the displays fan to shut-up. The consistent colour and quality of the display is why I picked them up. Apple support says bring them in for repair, but we both know where that would go. Any insight or assistance would be greatly appreciated. Thanks Team!
I suspect your Thunderbolt cable is bad on your Display #1 Its also possible your power supply is going as well so the logic board is not getting good power for the USB ports. While I know you want two displays working here lets see if we can use parts from one to diagnose the other. I’m going to suspect if you where to swap the displays the system which has the dirt on the backlight and has the fan running hard will become quiet with the other display (that would imply the thermal sensor has an issue or the screen is running hot). If you were to take the TB cable from the good system #2 and put it on system #1 the brightness control should show up and stay, if not then its the power supply.
