Used HHKB controller or USB problem

[mkleehammer]

I picked up a used HHKB Pro 2 on r/mechmarket and just got it today, but it spews things like "azxc34redfvb56ytghn1" and hangs when I plug it in to two Macs (which is all I have to test with).  The actual keys pressed are similar but not always identical - seems to go through all or most keys.  Any ideas what could be causing this or how to troubleshoot?

I have two other HHKB Pro 2 Type-S that I use on these systems and have no problems at all.

I ran the Keyboard Viewer which shows what keys are pressed. When I plug it in, it seems to run through most or all keys and then most of the modifiers stay pressed. No USB errors in the Mac system log (Console).

This was lubed and has new domes. The seller didn't mention any problems (I've just sent a message to discuss) so I'm assuming it worked for them. The switches were not set for a Mac and I did change them. (Incidentally same behavior regardless of switch settings.)

Does this sound like a controller problem? Could broken cables ever do that? Perhaps lube melting during shipping onto the PCB? The lube is 3204 which I assume is non-conductive so shouldn't do that.

Any suggestions on troubleshooting?

[Applet]

If you open it up, you can unplug the cable that connects the top PCB to the controller, and then connect only the controller to the computer. If you still get the same behaviour, it is likely a problem with the controller.