I just now happened upon this thread.
Flickering has been a problem in several of the Blaster II. The main reason was the contact between the srew and the negative solder contact. Tightening down the screw often solves the problem. I found a few that it took more than merely tightening down the screw. I had to add a tiny brass washer to the screw. The brass washer make the ground circuit more reliable.
I tested a couple of the next production run that had the same problem (still). So I have placed the brass washer on all subesquent Blasters, even if they didn't have the problem. All of the Blaster series flashlights will have this washer added, from the factory, from now on.
Just one of those things you never know about, until the product gets out in the field for testing.
Another problem the first production run had was in the tailcap to body ground connection. The end of the flashlight was left unanodized, and made contact to the cap. So, unless the tailcap was tighted securely, the light didn't get ground and didn't work, or would flicker. In this next production run, the threads were cut after the anodizing process, so they are bare aluminum, and make excellent electrical ground, even if the cap is very loose.
Wayne j