This is... not a story I'm really impressed by, all around, honestly. Although your mileage may vary, since I haven't yet found a way to ingrain my own opinions and beliefs into the rest of y'all. Yet.
Anyhow, it's Powell and Donnovan again, and again they're fairly flat characters, with Donnovan being the Dumb Angry guy with occasional inspirations out of left field, and Powell being the Calm Voice of Reason and Intelligence.
The writing itself is clunkier in places: "'Shut Up!' said Powell, savagely, 'I know you know it, but I'm just describing the hell of it.'" Did anyone not immediately tack "so that the audience can know what's going on" to the end of that sentence?
And it's nice to have Asimov admit that no one knows how the hell positronic fields work, including the guys in charge of maintaining and troubleshooting them. Unobtanium, indeed.
Even the problem du jour falls a bit flat for me, since I'm finding it hard to imagine that six "fingers," specifically, vs. five would really narrow down what circuits they need to check. I mean, if it's a matter of coordinating the fingers (which they had already figured out), why would the number of things being coordinated really narrow it down any more than knowing what the general problem was in the first place?
Of course, I'm not an engineer/computer scientist/roboticist so... I don't know. :p