No motor movement after rebuild following free-spin.

[twogowan]

Hi I'll try to keep it short,

Pre-owned MP5, took apart to install new spring and check what exactly the previous owner hsd induce.

Upon rebuild, I did not seat the motor correctly and it free-span a couple of times before stopping. 

Following this it no longer moves on trigger pull. Tried different battery.

Looking online people with similar problems have been told that fuse burnout is the probable cause, however upon checking the wiring there does not appear to be a fuse installed.

With there being no fuse, am I likely looking at a burned out motor?

Thanks for your time.

[Fatboy40]

From my own experience if the MP5 has a fuse it will usually be a small distance along the power cables from the battery connector (either a blade fuse or a cylinder in a plastic housing), however you may have a MOSFET / controller of some sort so if you do the fuse in a component of that.

 

I'd temporarily connect the motor to the terminals of another gun whilst leaving it outside of the gun (either hold the motor or put something heavy on it), pull the trigger on semi and get ready to disconnect the battery, if it spins then the motor's fine and either there is a fuse somewhere in the MP5 or the fuse in the MOSFET is blown (which means a new MOSFET unfortunately, unless you're able to replace surface mounted electronics). 

Edited July 25, 2023 by Fatboy40

[EDcase]

When you say "... it free-span a couple of times before stopping"

Do you mean you pulled the trigger a few times and it free span then it didn't move the next time you tried the trigger or you kept pulling the trigger and the motor just locked up?

The devil's in the details...

 

Its either a fuse buried in there somewhere or the MOSFET if it has one.

 

Its unlikely to be motor burnout but if you want to test...

As Fatboy said, test the motor ideally by connecting to another AEG or VERY CAREFULLY directly to a battery using wires/paperclips into the battery.

*MAKE SURE WIRES CONNECTED TO BATTERY DON'T TOUCH EACHOTHER*

Just tap the contact to see if the motor jumps but ideally put the motor in a vice.

 

 

 

 

 

 

Edited July 25, 2023 by EDcase

[twogowan]

Thanks for your replies guys. I'll post a couple images of the innards before I test the motor, that'll probably be better than me trying to explain whats in there. I attached em to the post.

 

Do you mean you pulled the trigger a few times and it free span then it didn't move the next time you tried the trigger or you kept pulling the trigger and the motor just locked up?

 

The devil's in the details...

 

______

To be as specific as possible, I pulled the trigger once for .2 of a second and heard a fast whirring which I assume was the motor spinning.

I repeated the trigger pull for the same result.

I repeated the trigger pull a third time and nothing happened. 

 

[twogowan]

I can see now the Perun mosfet inside has a fuse built-in (I'm new to exploring the innards obviously, I'm at that point I wish I'd just gotten a professional instead of trying to do it after watching a few youtube vids).

I'm reluctant to pull the motor out of my backup AEG right now incase I bugger that up too and have nothing to play with this week so I'll try that paperclip test, if I can find one that is. Either way the gun will be down for the count till payday I'm thinking.

[ak2m4]

you sure you didn't reverse the polarity of the motor?

[Emergencychimps]

24 minutes ago, ak2m4 said:

you sure you didn't reverse the polarity of the motor?

Check this first, easy to do and done several times! 

[EDcase]

With a reverse motor connection I wouldn't expect the motor to spin but I guess its possible it could spin inside the pinion gear.  That would likely blow the MOSFET.

[Emergencychimps]

It would spin the motor, it just spins the motor the wrong way as you have reversed the polarity (man, this sounds like some back to the future stuff). Assuming there is an anti reversal latch that would prevent the gears from turning. 

 

If the motor wasn't properly seated and therefore not engaging with the gears, this would explain why it did turn before it was seated properly (not engaging gears) and didn't turn when it was seated properly (engaging gears). 

 

 

[Leo Greer]

It's possible the actual MOSFET chip is blown, but usually that makes the motor spin whenever the battery is connected, not only upon trigger pull.

[EDcase]

6 hours ago, Emergencychimps said:

It would spin the motor, it just spins the motor the wrong way

If the pinion gear is engaged with the bevel gear which they should be when the motor is mounted in the handgrip then it cannot spin backwards because of the anti-reversal latch.

OP said motor wasn't mounted correctly but I can't imagine how it would not have engaged the gears at all.

 

 

Edited July 26, 2023 by EDcase

[twogowan]

Thanks for the replies guys,

3 hours ago, EDcase said:

If the pinion gear is engaged with the bevel gear which they should be when the motor is mounted in the handgrip then it cannot spin backwards because of the anti-reversal latch.

OP said motor wasn't mounted correctly but I can't imagine how it would not have engaged the gears at all.

 

 

I have been working on the assumption that because I neglected to screw in the small screw that allows you to adjust the motor depth, it ended up not touching the gears and span inside, based on the whirring noise I heard on trigger pull. I can't confirm anything of course.

I don't believe the polarity was reversed as there is a positive marker on the side of one of the motor connections along with a red marking which I attached the red wire to and the black on the other side.

After tomorrow's game I'll pull the motor out of my other AEG and test the MP5's motor on those wires.

[EDcase]

1 hour ago, twogowan said:

Thanks for the replies guys,

I have been working on the assumption that because I neglected to screw in the small screw that allows you to adjust the motor depth, it ended up not touching the gears and span inside, based on the whirring noise I heard on trigger pull. I can't confirm anything of course.

I don't believe the polarity was reversed as there is a positive marker on the side of one of the motor connections along with a red marking which I attached the red wire to and the black on the other side.

After tomorrow's game I'll pull the motor out of my other AEG and test the MP5's motor on those wires.

Yes, that sounds about right.  If the adjustment screw wasn't in at all then the gears must not have been in contact at all.  That would also mean that it wouldn't matter if the motor was wrongly wired.

I would guess the free spin of the motor must have overloaded some part of the MOSFET board.

If its the MOSFET then it should be relatively easy to replace with a basic one.

[twogowan]

On 27/07/2023 at 00:57, EDcase said:

Yes, that sounds about right.  If the adjustment screw wasn't in at all then the gears must not have been in contact at all.  That would also mean that it wouldn't matter if the motor was wrongly wired.

I would guess the free spin of the motor must have overloaded some part of the MOSFET board.

If its the MOSFET then it should be relatively easy to replace with a basic one.

Okay so I tested the motor on the other aeg wiring and it span fine.

Had a look at the mosfets manual and the status led had no indication of an electrical issue.

So I think I'm looking at a case of me being a silly billy at some point along the line. I'll try rebuilding it again later and see if anything happens.

thanks for all the inputs on this

[EDcase]

Good luck and let us know 👍