On Thu, 23 Dec 2010 12:22:35 -0000, "N_Cook" wrote:

So what likely went wrong with the laser? Old and new both measure about
0.65V DVM diode test but powered in circuit the old one was dropping 4.6V
over the diode and the replacement, working one, about 1.8V across the
laser.


The old laser has ceased to lase, though damaged ones may still emit light
(IR). You old one apparently does not even emit light, thus the high
terminal voltage from the (IR) output regulation circuitry.