I can't imagine a bad relay board would blow a fuse. The relay board would need to make a bad connection to ground to blow a fuse -- I don't see it.
If you could supply me with the ML#, I'll take a look at the wiring diagram and give you an educated answer.
Not that I recall clearly which fuse is for the drain solenoid, but the two sound related. If a drain valve is obstructed by debris, it will heat up the coil and short it out. I don't know the spec'd ohms, but I would suspect at least 50. I'd check it.
This is a low temperature machine. So detegent and sanitizer go in together and the rinse aid goes in at the rinse cycle. At the lines in the right containers. It is pulling sanitizer at the rinse cycle?
Page 11 of the manual leads me to belive it may be priming. Do you have non return valves in the lines of all the product? Your lines should be full of chemical all the time with no air spaces.
Your detergent supplier, Hobart, Ecolab, Diversey will often help with issues like this for no charge. Don't let them play with metering though. That is an old trick to get the salemen more sales. ;>)