It's an interesting point, dc42, and something we've been mulling over, especially since we went 'big time' with RS!
Our general policy is that it is your printer, and you are free to do what you want to it. It's the nature of machine evolution that Adrian Bowyer promotes, that by Open Sourcing the design, people are free to make their own choices, and the printer can develop independently of us. We feel that our responsibility is to get you printing, and will support you as much as we can to get as many of our customers as possible to that point. Parts that are missing, supplied incorrectly, and broken during assembly (especially if the instructions aren't clear) will be replaced under warranty. If a customer decides to diverge significantly from our instructions, we feel we can't be held responsible for that choice, and the warranty will be void. That's not say we won't continue to support that customer with advice, but the limits to the warranty have to be realistic.
Once the printer is operational, and something breaks, we try to work with the customer to diagnose the problem, and come up with a solution. This can feedback into the instructions, and/or inform the customer so they do not repeat the mistake. If replacement parts are needed, we generally need some evidence that failure is our responsibility, rather than the customer's, to authorise warranty replacements. We're pretty good at knowing what can go wrong!
The case for the first 220 Duet boards is that they have been supplied functioning, but not fully functional. It depends how each customer intends to use their printer as to whether this is a problem for them or not. We're aiming to do a 'managed' recall, so that we have enough boards, and time, to cope with the turnaround over a couple of months, rather than all at once. We would like these returned to us, as we can then send them back to the manufacturer to be fixed. If a customer tries to fix the board, and fails, that becomes more difficult, and will be looked at on a case-by-case basis.
I think, in the end, it's down to common sense. If you KNOW that fixing the board is within your capabilities, I would say fix it. If you THINK that you MIGHT be able to fix it, I would advise against it. You may left with a properly broken board, and we may be more circumspect about replacing it, depending on the damage done to it - tracks lifted being the worst, as it makes the board unrepairable.
If there already other issues with the board, eg some customers have reported loose/poorly soldered USB connectors and SD cards, I would say DON'T fix it; return it for a warranty replacement, with a note of the fault. That way, we can feedback to our supplier, and get them to improve reliability.
I hope that helps.
Ian
RepRapPro tech support