Also make sure all the little screws, one on the side and one on the bottom cap are ticht. The one on the side you might work it back and forth a few times in case it has anodizing under it.
I've been having the same type of problem. Its an older Buzz. Without a carto on the top I get a red and blue light on. When its firing, and without a carto on, the red light will disappear. When I put a carto on the blue light goes away and just has a red light. When I hit the button a blue light comes on and the red light goes away. This is "normal" behavior. Whats been happening is that it wont fire at all, either with or without a carto attached (I use SmokTech 1.5 LRDC's). Without a carto I get both blue and red led's but when the button is pushed the red light stays on. When I put a carto on the blue light goes away, but when I press the button the red light stays and no blue light. I also have tried cleaning, fresh batts, etc. Nothing I does at the time will fix it. However, it will start to work again on its own. No rhyme or reason to it. The only thing I could think off is juice is getting into the connector and causing some sort of short. Right now its been working all day and I've taken to removing my DCT and cleaning the contacts every hour or so. We'll see if this keeps it running for good.....
Ok, back to having the same issue. I FINALLY got the top cap off (as I said, previous owner used thread lock on it, maybe part of the problem?) and cleaned the centerpost, screw and top cap. Cleaned bottom cap and made sure spring was good. Same thing. With no carto on 510 connection I get a red and blue light. Hit button and both lights stay on. Put a carto on and the blue light goes away, red light stays. When button is pressed nothing happens and I only get a red light, no blue light. Could this be the switch going out? What I have seen after messing with it many times is that sometimes if I hold the button down long enough it will fire, but cut off again a few seconds later. I've tried all three sets of 16340's I have, same result. Checked batts with a multimeter, fresh off the charger they are hitting at 4.18v. Going to soak the center post and both screws in alcohol tonight and see what happens. I'm not very positive that this will have any effect though as its registering when the carto is on the connection (blue light goes out) it just will not fire, which leads me to believe the button is shot.
Already checked all that. Measured the resistance between the center post and the sidewall, showed an open connection. I've already pulled the entire top cap apart, even took the center post off the positive wire and cleaned under its contact. I've thoroughly cleaned everything with a cotton swab and alcohol then compressed air to make sure no cotton fibers were sticking around. Also, tried a couple of different carto's, and all of them fired fine on my silver bullet, so I KNOW its not a carto issue.
Also, the behavior its showing is systematic to a button failure. Everything works like it did before, it just wont fire. With no carto I get both red and blue lights, but when I put the carto on the blue light goes away showing that the circuit is now complete. If it was shorting out I wouldn't have a blue light at all regardless if the carto was on or not. Is there a way to pull the circuitry out so I can ohm out the switch while depressed?