The problem I think is deeper. There are parts that are obsolete on that board, let alone those with firmware loaded. There are no design drawing out there. They are multi trace layer boards. I have my process down to a science for 3V boards. But still can't fix them all especially when the 5V and 3V buss is fused internal in the PCB. Or the main processor looses a function from a short that is critical. 3V went obsolete for the same issues of specific chips no longer available. Just compare it to a 3V and realize even if you fix one chip, another is about to fail on a 5V. So unless your going to remove and replace all through hole and major SMD devices like diodes and FETs. I think we had some one over a year ago going down this same road. Never heard it was successful.
I am just saying pick some thing that the design was better to start and actually a desirable part. It took me about a year and half to reverse engineer the 3V boards and fine how it worked, and it was a much simpler device. Then another year or so of finding common modes of failure. We have no idea how the 5V fails. We just know some are total dead, and other have direct shorts. No real insight except the PV diodes, the rectifier, the swelling cap. Audio amps, light fets and motor fets, no problem. Everything else 
G
