View Full Version : Mechbox trigger question

Mad Irishman
03-04-2007, 09:49 PM
After replacing the gears and shims in my TM Beita I started getting a problem with the gun stopping while firing.I was trying to settle the new spring by going through a few hi caps. The gun would fire about 50 or so rounds then stop. The trigger would depress smoothly and I didn't notice anything that seemed like binding. It was as if the gun wasn't getting voltage. At first I could move the selector to safe and back to get a few more rounds out then it would quit again. I used 4 different batteries to verify then cracked open the mechbox again. I found that the trigger switch was not seated flush with the bottom side (left) of the mechbox. Once I seated it the gun started to fire smoothly again. Now the problem I am having is that when you look at the left side of the mechbox where the trigger selector make contact with the trigger switch, you can see a small blue arc every time the trigger is pulled! :eek: I can't imagine that this is normal but I've never watched it before. Any ideas on what's going on? Is this normal?

03-04-2007, 10:02 PM
I don't have experience with the version 3 mechbox, but I do have a wild suggestion based on some symptoms I had recently. Check the two springs on the end of the motor, ensuring that they're properly engaged with the motor brushes. On my M4 I had managed to bump one of these springs loose during tear-down, and this caused intermittent arching in the body.

Mad Irishman
03-04-2007, 10:14 PM
The two springs appear to be in the right position. I've never removed them so I'm not positive but they look correct.

03-04-2007, 10:49 PM
Does the selector plate move across two copper contact bars on the left side of the mechbox? If it does, I'll bet that the two contact bars are somewhat depressed from their original position. While disconnected from a battery, place a small screwdriver underneath the contact bars and very gently bend them back into their original position so that they make proper contact with the selector plate.

Mad Irishman
03-04-2007, 11:21 PM
Woot! Who's the man? Marimba...Marimba.... That worked like a champ! Thanks bro!

03-04-2007, 11:27 PM
That is a common problem with Ver3 mechboxes as they age.

Mad Irishman
03-05-2007, 01:21 AM
Thanks for the help guys! I hope to get a better crono reading now that I replaced the Systema spring with a CA. Didn't really find anything that was causing the low numbers with the M120 spring that was in there though (290fps).