CYMA MP5 - Semi auto broke

[LukeNorman]

I have been searching the internet for an answer but none have been able to help.  
In full auto the RIF works amazing but in semi auto it is iffy, either doesn’t shoot but spins the motor, doesn’t do anything or sometimes it works. 
 

I stripped the RIF down to the motor and gearbox and the motor works when pulling the trigger in semi. I am stuck with what the problem may be or even how to diagnose it further. Does anybody have any experience with fixing a problem such as this. 
 

The batteries are brand new, 7.4v lipos and that was my first thought. But it does have an upgraded SHS motor and 13:1 gears. 
 

cheers 

Edited November 21 by LukeNorman

[ButcherBill]

Have you tried different mags?

[LukeNorman]

Yeah, does the same with 3 different mags. 

[ButcherBill]

Then have you tried different batteries 9.6 or 11.1's?

 

A 7.4 might not have the oomph for the motor to be consistant.

Edited November 21 by ButcherBill

[LukeNorman]

I’ll give a 11.1v a go, just was worried about burning out the contacts as there is no mosfet.

[Colin Allen]

When you say that it doesn't shoot, what do you mean?  Do you mean that the gearbox does not cycle or that it cycles and no BB's come out if you have a loaded magazine in it?

Do you know the rating of the spring?

[LukeNorman]

Hey, cheers for the reply. I have a video of it just clicking when the trigger is pulled, but before it would sometimes cycle and shoot. 
 

the spring is a m100

[ButcherBill]

I still think it's the battery power, can't explain why it'll fire in auto tho. Collin has more experience that me & migt have an answer. 

[LukeNorman]

Got a 11.1v lipo coming tmr so I’ll update to see if it helps or not. I hope it is the battery and nothing else 

[Colin Allen]

Try the new battery; however, it looks like your trigger is not always resetting properly in semi.  I suspect it is some sort of trigger trolley/trigger interface/COL issue; it might be that the trigger is not engaging with the trigger trolley properly due to wear on one or both or that the COL is engaging badly with the trigger trolley.

If the battery does not do the trick, you are going to have to open the gearbox up.

[Lozart]

11 hours ago, Colin Allen said:

however, it looks like your trigger is not always resetting properly in semi.  I suspect it is some sort of trigger trolley/trigger interface/COL issue; it might be that the trigger is not engaging with the trigger trolley properly due to wear on one or both or that the COL is engaging badly with the trigger trolley.

 

 

I agree, this doesn't seem like a battery problem to me. Most likely the trigger contact trolley or the cut off lever is a bit worn. Good opportunity to sack it all off and fit a decent ETU.

[Cannonfodder]

15 hours ago, LukeNorman said:

I’ll give a 11.1v a go, just was worried about burning out the contacts as there is no mosfet.

Nothing to worry about there, I've been running most of my AEGs with 11.1v batteries and no mosfet for years with no problems 

[Ace Airsoft War Games]

Hi, I had this issue with most of our CYMA MP5 rentals using NIMH or 7.4 Lipo, would fire no problem on full auto but semi would be very hit and miss if at all.
After lots of head scratching we noticed that on full auto people tend to usually pull the trigger quite hard and it fires, so we tried the same principle on semi pulling the trigger like really hard and IT WORKED every time!!  Turned out to be worn out and dirty internal trigger contacts in the end.

Hope that helps.