Thank you for posting that. In recent years, it has gotten somewhat more common for builders to use brazing flux or repair flux on their kits, and this flux is conductive and causes a whole ton of issues. I could tell in your photos that some extra flux had been used, so I thought it was worth asking. The rosin core in the solder you used is the flux, so you don't need to use any extra.
With your black meter probe grounded, what DC resistance do you get between each end of each 270 ohm 5W resistor?
I would also assume that all of the measurement tests before the final one were done without the fuse blowing?
Generally what I expect when someone reports a fuse blowing immediately upon powering up a Crack is that a UF4007 diode is installed backwards, the leads of two diodes that go to two different terminals are touching, a 220uF/250V cap is installed backwards, a black ground wire is installed into an improper terminal, or a 270R/5W resistor is installed into an improper terminal. I don't see any of this going on in your photos.
We can split the circuit in half for the purposes of testing though. You can remove the red wire at terminal 13 and bend it up and out of the way, then fire up the amp and see if the fuse holds (I would be surprised if the amp was suddenly happy, but it's worth the cost of the fuse to see).
-PB
