The most important thing, IMHO, is what you did before having a radio failure.
That is ensured you knew your destination's non-radio join procedure, and if they won't accept non-radio traffic under any circumstances - have decided upon a radio-failure diversion (and known their procedures).
(Almost) invariably this will also require you to be up to speed on how to fly an overhead join and read the signal square.
Apart from that I'm with A_and_C, don't muck about with diagnostics in the air, concentrate on flying non-radio, and do your investigations on the ground.
G
Suffered this too often!