Hi Dave, so the same robot plugged into a different controller homed fine? Just making sure.
Also, do all axis show the same sluggishness?
The control box (Scorpower) is more like a power supply, really. That and the driver for the motors. All the controlling is happening inside the software on the PC. But as far as what voltages to expect inside the box, there should be +5V and +12V in there.
I actually had to repair my Scorpower USB box myself before I could use it. From my own experience and hearing from other Scorbot enthusiasts, the large electrolytic capacitors in the power supply very often go bad. Mine had the cap on the input side on the +5V voltage regulator shortened. I had to replace the cap. Another possibility is the voltage regulator itself could have given out. These are pretty archaic linear power supplies and they use the classic 7805 for 5V and 7812 for 12V regulators, except they are using rather hard to find 3A versions. Most of what's sold out there is 1A, so be careful if you're looking for places to buy one.
I am thinking there's nothing wrong with the +5V branch since otherwise neither USB nor lights would work on the box, it'll just look like it's completely dead. On the other hand, if 12V is not quite 12V, it may explain the sluggishness. Maybe there's yet another shortened or dried out capacitor, this time on the output side of the 7812 regulator?
Unfortunately, the PCB is a real pain to remove - it's bolted down to everything really good. But once you get it out, the repair (if it is indeed power-related ) should be relatively easy. Pop the old capacitor, put the new one in. If it did not fix the issue, replace the 7812. That should do the trick.
Of course, there could also be something entirely different that I can't see. Let's just hope it's not the transformer that feeds that 12V regulator. A replacement for that puppy would be next to impossible to find and no one in their right mind would rewind a transformer these days.
Anyhow, I hope it's something less dramatic. My guess is that a dried out or shortened electrolytic capacitor is the culprit once again.
Good luck!