gunrunnerjohn posted:...
As far as testing for open, it's a lot more complicated than an ohmmeter. You need a current limited variable voltage supply to test the breakdown voltage of the TVS to see if it's still meeting it's specs.
So what is the thinking on preventative-maintenance or testing a TVS? 
I think you could count on one hand the number of OGR'ers with a current-limited power supply that goes up to ~40V.
Soooo. I was thinking maybe a 25 cent capacitive voltage-doubler circuit that would convert 18V AC that presumably every O gauge user has to higher voltage DC...then use any DC voltmeter with and without the TVS to see if the DC output clamps to ~33V, ~36V, or whatever. The key point is the low-cost of this "tool". If there is interest I can elaborate.
Or, to Paul's point, maybe everyone replaces all the TVS diodes (good or bad) on their layout at the same time they change batteries on their smoke detectors? 
