Generally transformers either work or they don't work - I have never encountered an intermittent transformer although I'm not a qualified electrician - instruments & computers since 1962.
I suffered with continually failing, over-counter kitchen downlights - four of them at 12v 20W fed from transformers.
The main problems apart from the fillaments failing were ones of poor connection - I remade all the connections and things improved but the lamps still continued to fail but much less often.
I think the installer had not stripped back the insulation on the wires properly and had just relied on the screw terminals to puncture the plastic to make the connections
In desperation at always fiddling around with the expensive lamps when they really failed I replaced them with miniature neon strips at about £9 each - just one tube to replace in 2 years - better light - more relaible - cooler - cheaper to run.
Good luck...
Peccavi
March 2010
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