Problem: My gun goes full auto, and can't stop firing. Why is that.

Question:
I realy need some help with my gun. As soon as I put my battery in the gun, the replica starts to autofire and it don't stop. I didnt drop the replica or hit or anything it just happend. Can you help me please.

My repply:
Hello
There are a coupe of ways a gun can have the behaviour you describe...
Here comes an eksplanaion on the ways that this can happen:

Option nr 1.
-----------------------------
Most older gun's does NOT have a mosfet installed from the factory. But if some one has installed a mosfet? Then the mosfet could be burned...
When a mosfet end's it's life then the gun will always go full auto. This is a verry normal problem with gun's that has mosfet's.
The fix: Replace the mosfet...

Option nr 2.
-------------------------
If the gun you have is verry used / old. Or if you are using Lipo / Life batteries. Then there is a good chanse that you trigger contacts are burned together in the on position .....

Option 2.a. (Old gun)
With time all airsoft triggers build up small burn marks that over time can make the trigger contacts have baad electrical contact points... When this happens then the contacts will make bigger and bigger sparks when pulling the trigger ... and eventualy the contacts burn together .... This will meen that the contacts can't release ..... ergo full auto ...
The fix: Clean the trigger cobber contact plates inside the gearbox...

Follow the link on the above line below... The last image shows the trigger that needs to be cleaned ...
GearboxV3_Page1

Option 2.b (Lipo)
Lipo and Life batteries gives ALLOT more power to the motor when using them ... The down side is that this ALSO burns the trigger contacts ... And after some time the trigger contacts will burn together .... Just like option 2.a but with lipo's this happen alot faster ...
The fix: Clean the trigger cobber contact plates inside the gearbox...

Follow the link on the above line below... The last image shows the trigger that needs to be cleaned ...
GearboxV3_Page1

Not: When you use lipo batteries you should ALWAYS have a mosfet installed !!!!!
Mosfet_Page1
It protect's the trigger contacts .... On the mp5k the mosfet can be hidden in the front grip when installing it ....

Option 3.
----------------------
Short's ... If the wires break inside the gun the metal frame (on the cyma mp5k the body is metal) can come in contact with the wires and then the body can carry the power to the motor... The nagative side (black wire) of the gun is directly connected to the battery... If hte wires on the battery side of the trigger touches the frame, and the motor side wires also touches the frame then the power conection is done and to motor will go full auto ...
This is ALMOST NEAVER HAPPENING !!! This amlost only happens when the gun get's disassembled and re assembled ALLTO of times .. 10-20 or more ... Because the wires each time will get bent and cut ....

Summery
-------------------------
The most ovious reason would be if you have a mosfet then is't 99% that it is blown and needs to be replaced ....
If you are using lipo's... Then it's 80% chance the trigger contacts are burned together. Clean them and install a mosfet !!!
Do you have an old verry used gun then it may also (60% chanse) be burned trigger contacts ... Clean + Optional install mosfet...
If none of the above are likely then it may be the wires that have broken .... Installe new wires ....

I hope it was helpfull ...
If you want to try to fix the problem your self then take a look at my guides to disassembly og the gun and gearbox.
Disassembly


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Airsoft Front Calculators CronoPhone Projects and tech Mods and Upgrades Disassembly FAQ & QNA Links	Problem: My gun goes full auto, and can't stop firing. Why is that. Question: I realy need some help with my gun. As soon as I put my battery in the gun, the replica starts to autofire and it don't stop. I didnt drop the replica or hit or anything it just happend. Can you help me please. My repply: Hello There are a coupe of ways a gun can have the behaviour you describe... Here comes an eksplanaion on the ways that this can happen: Option nr 1. ----------------------------- Most older gun's does NOT have a mosfet installed from the factory. But if some one has installed a mosfet? Then the mosfet could be burned... When a mosfet end's it's life then the gun will always go full auto. This is a verry normal problem with gun's that has mosfet's. The fix: Replace the mosfet... Option nr 2. ------------------------- If the gun you have is verry used / old. Or if you are using Lipo / Life batteries. Then there is a good chanse that you trigger contacts are burned together in the on position ..... Option 2.a. (Old gun) With time all airsoft triggers build up small burn marks that over time can make the trigger contacts have baad electrical contact points... When this happens then the contacts will make bigger and bigger sparks when pulling the trigger ... and eventualy the contacts burn together .... This will meen that the contacts can't release ..... ergo full auto ... The fix: Clean the trigger cobber contact plates inside the gearbox... Follow the link on the above line below... The last image shows the trigger that needs to be cleaned ... GearboxV3_Page1 Option 2.b (Lipo) Lipo and Life batteries gives ALLOT more power to the motor when using them ... The down side is that this ALSO burns the trigger contacts ... And after some time the trigger contacts will burn together .... Just like option 2.a but with lipo's this happen alot faster ... The fix: Clean the trigger cobber contact plates inside the gearbox... Follow the link on the above line below... The last image shows the trigger that needs to be cleaned ... GearboxV3_Page1 Not: When you use lipo batteries you should ALWAYS have a mosfet installed !!!!! Mosfet_Page1 It protect's the trigger contacts .... On the mp5k the mosfet can be hidden in the front grip when installing it .... Option 3. ---------------------- Short's ... If the wires break inside the gun the metal frame (on the cyma mp5k the body is metal) can come in contact with the wires and then the body can carry the power to the motor... The nagative side (black wire) of the gun is directly connected to the battery... If hte wires on the battery side of the trigger touches the frame, and the motor side wires also touches the frame then the power conection is done and to motor will go full auto ... This is ALMOST NEAVER HAPPENING !!! This amlost only happens when the gun get's disassembled and re assembled ALLTO of times .. 10-20 or more ... Because the wires each time will get bent and cut .... Summery ------------------------- The most ovious reason would be if you have a mosfet then is't 99% that it is blown and needs to be replaced .... If you are using lipo's... Then it's 80% chance the trigger contacts are burned together. Clean them and install a mosfet !!! Do you have an old verry used gun then it may also (60% chanse) be burned trigger contacts ... Clean + Optional install mosfet... If none of the above are likely then it may be the wires that have broken .... Installe new wires .... I hope it was helpfull ... If you want to try to fix the problem your self then take a look at my guides to disassembly og the gun and gearbox. Disassembly
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