2012 Prius MFD Headunit Malfunction, Removal of Harman Extension Box, Possible Fix (Solder Joint)

I had the dreaded MFD malfunction in my 2012 Prius III with the Navigation MFD/Headunit (no JBL), and wanted to share my experience researching this problem.

Members here and elsewhere believed that the Harman Extension Box that's an auxiliary component to the MFD was the culprit. Sure enough it was. I removed a bunch of trim pieces to get to my stereo, and then I disconnected all the connectors to the Harman box.

The MFD worked, but lost the Apps, Navigation, and Entunes.

People seem to believe that Bluetooth was also lost, but this is not true. If both connectors [see red lines in "MFD Back" picture below] from the Harman box are re-connected to the main unit, then Bluetooth works fine to wirelessly stream music from your phone.

This is where most discussions on this problem ended.

I believe the failure mode is very likely to be a solder joint problem. My MFD would work on and off depending on the day before dying for good -- this is very likely a due to a broken solder joint.

I took apart the Harman box. It's held together with six T10 torx screws. The PCB inside comes right out, nothing other than the screws holding it inside the enclosure.

Looking around the PCB, at least one of the pins holding the large main 24-pin connector appears to have a bad solder joint.

With a soldering iron, the joint could be fixed. After re-soldering, I would probably also conformal coat the PCB to last a while longer in the heat.