You're probably right. The original PSU works just fine with the third module disabled, so it's likely that just a part of that module is damaged. When I get a chance I will take it apart and inspect the module. It would suck if it's the backplane that's damanged as two modules connect to one backplane. I must admit I'm not a big fan of the batch3 design. As of now the unit is hashing fine with two modules and with the original PSU in place.
I'm thinking of selling the unit. I am getting tired of babysitting these units.
If anyone wants to make me an offer for the unit (bear in mind that at the moment only two modules are officially functioning) please PM me.
The b3 backplane easily breaks apart in order to separate the modules, there are no electrical connections between the 2 modules on the same backplane.
Possible magic smoke sources on the backplane are the power connectors, 2 caps on the bottom side, or worse case circuit traces.