You are welcome, Mark. It seems that there was a QA issue with some of the outsourced modules. I believe that you will qualify for a replacement module(s) and get a $50 discount on the upcoming rotary module by way of thanks for your patience. Good that you managed to pin down a solution and hopefully it will be a permanent fix. I saw somewhere (cannot remember where I read it though) that a couple of overvoltage diodes appear to be missing from the faulty modules.
wait one… I think it was @Toxic. Ok found it.
Circuit diagram linear module? or why my linear module is broken