The plastic tang on the blue trigger had broken off.
I fixed mine by disassembling it and gluing a steel rod in place of the plastic actuator tang.
The top blue cover on the handle lifts off, the latch tabs on the plastic are hidden. You may need to gently pry it off with a flat bladed screwdriver. You may cause some cosmetic damage, but it's worth it. The unit was clearly designed as a "throw away".
The faulty trigger mechanism is a design flaw, and simple to fix with some gorilla glue and a 3/4 inch piece of shank(smooth part) of a 3/32 inch drill bit.
Phil
May 2008