Unit 3 Failure

Got a trusty old MJ Research Tetrad PTC-225 4 block Peltier Thermal Cycler with standard 96 well Alpha blocks. Darn thing displayed a Unit 3 Failure this morning during Self-Test. I swapped blocks, but no luck. The manual states "The self-test has failed because of a problem with the base or the Alpha unit." And no more info other than to call MJ (now Bio-Rad). Bio-Rad gave the usual "out of support and thus we have no specific info." This unit is very nice, so it seems worth it to repair. Anyone have any experience with these units?