I have had no satisfaction from BitMain and have decided to give up trying - at least I'll save myself the cost of shipping the other blown board to them for them to ignore.
I got two new boards from the very satisfactory Centrix International. I also bought their panel kit - it looks very smart and my new S5 is cooler and quieter than before, even with the stock fan.
Now all I need is advice - I will trawl this BB for answers to:
1) What do I do with the new % fan speed option? Is it safe to drop it very low if the temp stays low?
2) How about controlling heat and noise by under-clocking (to keep the noise level down at night time)?
3) Will two of these be better than the stock fan: 2 x Scythe Ultra Kaze Fan 3000 rpm 120 x 120 x 38 mm? Can I run safely on one of these?
4) How far should I push the clock when nobody is in earshot and going to be annoyed by the noise? Is it just a matter of going as high as I can without passing 70 degrees?
1) If you have a consistent ambient temperature and don't see that changing, set it as low as you want while monitoring temps
2) That's fine.
3) I've not tried them but others like them - I think it depends on your ambient if you can get away with one. Search (via google) the S5 thread for people's reports on them.
4) Don't bother pushing them, they're already near maxed out. You end up with less hash rate when you go too high because it starts giving you garbage results. With no voltage control on a string miner, just take stock speed as the max.