In adding science fantasy elements to a setting, we are leaving open the possibility that PCs will find high-tech items. I've mentioned previously that these in general should not be reproducible, so that the society doesn't wind up migrating from fantasy to science fiction entirely. But there are other possibilities, particularly because technological artifacts will by nature be prone to breaking, and weapons will run out of ammunition, and all of them will run out of power eventually.
So how do PCs find out if they can jury-rig a solution? I'm thinking that this is a good place for some Judges Guild style tables, akin to some of the things from City State / Ready Ref Sheets, giving a series of cascading chances to scrounge spare parts from other artifacts, rig up a solution, and of course what happens when it works or doesn't.
When the PCs run out of juice on the ray gun and the personal shield is malfunctioning - I'm thinking that the rules should allow them to sacrifice one artifact to salvage another with some reasonable chance. Or perhaps they go looking and find an inoperative beam rifle from a different period and manage to mix and match a few parts and get it to work - if nothing else, it's cool if it works at least once for a big boom before it is totally useless.
The chances of malfunction should always be present, barring a major success; if you have two identical pistols and replace one's firing mechanism with the other's, that will work reliably. But for the most part there needs to be some chance of backfiring, fizzling, or exploding, perferably in the most entertaining way possible.
Extending this idea, I'm thinking that a chart of different high tech weapons and defenses, combined with a set of rules for jury-rigging fixes, perhaps that can also double for what happens if they use malfunctioning equipment. Any special requests or ideas for this? It'll be for Dungeon Crawl #3.