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Medium In-Depth Issues and Solutions for AEG Users

This is a comprehensive article on discovery the issues and solving them for automatic electric guns.

I will try and make sort of a bracket of what the possible issue(s) is (are) and the possible solutions. I will not be going into bizarre issues and cases that have come up that deserve a spot on the tech hall of infamy. I will be going over the issues that are common. *Some are still, more common than others.

Gun Does Nothing On A Fully Charged Battery- (No MOSFET Installed)

Possible Issue 1: Your Fuse has blown.

Solution: Replace the fuse with another fuse with an AMP rating of 20
~40 AMP or by pass it temporarily, to ensure narrow the issue down to the fuse.
Possible Issue 2: You have a break in connection at the motor.
Solution: Ensure red (+) black (-) wires are firmly connected to the motor or in some cases soldered.
Possible Issue 3: Your trigger contacts are, Burnt from Arcing, Broken, or the male sliding contact is not touch one or more of the female contacts.
Solution: Clean the trigger contacts or replace them if they are broken. If they are simply not coming in contact with the each other, bend them in a way that they do. You can narrow this issue down several ways, if you don’t have voltmeter handy, take apart the mechbox, reassemble the mechbox with your trigger and complete trigger switch (trigger switch, trigger trolley, trigger trolley spring, and wires of course) are in only . Connect the motor plugs to the motor, hook up your battery, and pull the trigger. If it spins your good, if not you need to re-adjust the female contacts.
Possible Issue 4: If you’re running an AEG set up that requires a metal contact on your selector plate; make sure that, that selector plate contact is touching the outer contact(s) from the trigger switch. *This will be on the outside of your gearbox.
Solution: Bend the outside contact(s) so they are coming in full contact with the metal contact on the selector plate.
Possible Issue 5: If you are running regular Tamiya Connectors one or more of the crimped plugs has come out.
Solution: Make sure the wires are pushed into the plug as much as possible; the plugs should be even on both sides (jutting out the same length.) If the issue persists, it would be wise to convert to Deans connectors.
Possible Issue 6: Motor Brush Spring(s) have come off and are not pushing the motor brush or brushes (there is two) onto the armature of the motor.
Solution: Bush the brush or brushes (2) back in and properly re-install the spring(s) so they are pushing the brushes onto the armature.
Possible Issue 7: Cut Wire
Solution: Apply solder to complete circuit.
Gun Makes A Clicking Noise
Possible Issue 1: Your Gearbox is locked.
Solution A: Plug in a fully charged battery to your AEG, the battery needs to be of high quality preferably with a nominal voltage of 9.3 Volts or higher. Shoot the AEG and see if it will cycle. It should be noted that if your gearbox continues to lock up, you will need to get a new battery and/or purchase a higher torque motor- if your stock motor is way under powered.

Solution B: With at least the lower part of the GearBox exposed, stick in a strong thin, pick-like rod and push or pry the Anti-Reversal Latch up or to the side to get it off of the anti-reversal gear on the bevel gear. On stock guns this can typically be done every time, but with gearboxes using a strong springs (example 2 Joule or higher), you do have a higher risk of breaking the AR Latch on heavier springs as the gearbox is under more stress.

Solution C: If you cannot access the anti-reversal latch, the next easiest thing to do is open up your gearbox and reset everything to their relaxed position.
Possible Issue 2: Stripped gear with gear debris blocking teeth.
Solution: Replace the stripped Gear(s)
Possible Issue 3: Gears are shimmed too tight.
Solution: Re Shim the gearbox or have a tech re shim it for you, so that all gears are meshing properly, have no or very little play, yet so that they can spin freely.
Possible Issue 4: Motor height is to High.
Solution: Lower the motor height.
Loud Screeching Noise/ ‘Whirling’ Noise:

Possible Issue 1: Motor height is too low.
Solution: raise your motor height until the gun shoots normal, you are going to want to continue to raise the motor height adjustment screw right before you hear a drop in rate of fire.
Possible Issue 2: Pinion Gear shimmed too far away from Bevel causing insufficient pinion-bevel mesh
Solution: Add shims to the top of the bevel gear, forcing it to contact the pinion. If you are unsure about your shimming ask a tech or have a tech do it for you.
Possible Issue 3: Stripped Gear(s)
Solution: Replace the stripped gear(s) with an upgraded gear set.
Possible Issue 4: Gears shimming is way off.
Solution: Have gears re-shimmed properly.
Possible Issue 5: Exploded Ball Bearing.
Solution: Replace bearings to solid steel bushings or convert to ceramic bearings.
Gun Makes Plastic Grinding Noise And Won’t Shoot:

Possible Issue 1: Stripped Piston.
Solution: Replace piston with an upgraded one; be sure to correct the AoE.
*You will be able to see the air nozzle moving back and forth*
Gun Does Not feed All Of The Time:
*Before starting this, please make sure this is not a simple magazine issue.

Possible Issue 1: Air Nozzle not retracting far enough back to allow a BB to pass through the BB feed chamber.
Solution A: Shim the hop up away from the front of the mechbox. This is done by adding material to the back of the hop up sits further in front of the Gearbox shell. Note you should do this in small increments with trial and error. Try and not shim too far as you will lose a significant amount of FPS. You can use hard rubber, as long as it can be sanded and cut to shape.
Solution B: Like the solution listed above, you can add material to the front of the Tappet plate.
Possible Issue 2: Your Air nozzle is not being held back for a long enough period of time.
Solution A: Add a sector clip, if you do not have one you can make one.
FPS Is Much Lower Than It Should:

Possible Issue 1: Internal (Gear Box) Compression Leak. That is Compression loss via Piston Head, Cylinder to Cylinder Head, or Cylinder Head to Air Nozzle.
Solution: Please do a compression test and see if there is any air leaks when you press the piston head down. All of your compression components should be in top notch; this is pretty well known so I won’t dive into it. If you have a replace the parts with something that seals better, or even better, seal them up so they do not have an issue.
Possible Issue 2: Compression Loss via Hop Up:
Solution: Quality metal hop up and good quality bucking- Lonex and Prometheus are great options as far as consistency. It is wise to ditch the brass ring that “seals” the hop up to barrel and do the O-Ring mod, that will not only help with compression leaks and helps with accuracy, but will eliminate the need for a hop up spring. If you are unsure which O rings to purchase, HS5 makes them. If you do not have the O-Rings or anything to seal, Teflon tape seals nicely.
Possible Issue 3: Compression Loss via Air Nozzle to Bucking:
Solution : Use a shorter Tappet Plate, this is typically done by removing material from the front of the tappet plate (the bit that comes in contact with the front of the GB shell,) Do not remove too much material (if any) from the top portion of the tappet plate where the air nozzle sits. This modification, will allow the air nozzle to be pushed further into the hop unit hopefully creating a better seal from the air nozzle to the bucking, you can do this as trial and error as well, remove material, test, removal material, test, etc. It shouldn’t take too long.
Possible Issue 4: There is too much friction between Piston Head and Cylinder.
*This should have been noticed during the compression test, you should not have to force your piston through the cylinder.
Solution: Depending on what is rubbing up against the cylinder walls either the piston head itself or the O-Ring. Try another piston head. It should be noted this is an issue that will occur when you mix and match compression parts.
Possible Issue 5: One or more of your compression components is cracked and broken and causing an air leak.
Solution: Replace the broken part.
Hop Up Will not Adjust OR Adjusts Very Little:

Possible Issue 1: Your nub has come out of position on the hop up arm nub slot.
Solution: Disassemble the hop unit and reposition the nub correctly.
Possible Issue 2: Hop Gears are not turning one another. This is only pertaining to TM style M4/M16 Hop Units, both the one and two piece units.
Solution: Depending on if the plastic gears are broken or one has simply popped out of place and not making contact with other gear(s). If it’s broken you can still adjust the hop with the barrel out and rotate the final gear (the gear that adjusts the hop up arm) or you preferably seek a replacement set of hop up gears for your AR.
Possible Issue 3: Your nub is too soft or damaged-unlikely, but possible.
Solution: Replace the nub with a harder one – MadBull buckings are notoriously hard.
Possible Issue 4: Bucking is too hard
Solution: Switch to a softer one –Lonex 50 degree, SHS, Systema.
Possible Issue 5: Barrel window is not lined up with window in hop up
Solution: Disassemble and Realign hop up with barrel window.
BB Curves Laterally (Left or Right):

Possible Issue 1: Your bucking is misaligned or not seated on the barrel properly and the alignment ridge on the bucking is not lined up with the alignment cut in the barrel.
Solution: Re-align your bucking onto the barrel, if you are having trouble getting it to stay in place as try adding 100% silicone (liquid form to your bucking and then slide your hop unit over it)
Possible Issue 2: The mound that contacts the BB inside your bucking is inconsistent leading to inconsistent (left or right) trajectories.
Solution A: You can try the Dental Floss mod (if you do not know about this Google it)

Solution B: Purchase a new bucking.
Possible Issue 3: Your barrel is clogged with dirt and debris.
Solution: Clean your bore, it is not an option.
Possible Issue 4: There is too much play between the hop up arm and the hop unit.
Solution : Shim the hop up arm; this is done by adding an even amount of material on both sides of the hop arm, so that there is not side to side movement. I have not yet done this, but it seems metal sheets (aluminum and brass) are the preferred method of doing this.
Battery, Motor, Wiring Get Hot-When Firing:

Possible Issues: There is too much to stress on the Gear Box - This either the gears are shimmed too tight, the motor height is raised too high, the spring is too strong for your battery and/or motor.
Solution: Make sure your shimming is sport on, if you’re shimming from the bevel gear, you shouldn’t really need to adjust your motor height when it is completed. If you are pulling a heavy spring, you should already be running a torque motor (neodymium magnets). Torque motors also tend to run cooler than speed motors as they have more windings, typically.
Other common Issues associated to Gear Box stress: The piston is too tight and cannot cycle- this is pertinent with aftermarket pistons on certain GB shells.

LiPO Gets Warm when shooting:

Depending on your set-up, you will most likely need a higher rated ‘C’ LiPO.

If you are using a relatively low stress set up, you may need to revert back to fine tuning your gearbox, as there may be unnecessary stress.

Trigger Jams in Semi-Auto:

Possible Issue 1: Your Sector gear is stopping in a certain position, this position is having the cut off cam on the sector gear already engaged with the cut off lever, so the cut off lever is actually blocking the trigger trolley from being able to move forward.
Solution A: Use a better battery.

Solution B: MOSFET switches do help. Active braking will cure the issue, but will result in increased wear and tear on your motor/brushes and cause additional heat.

Solution C: If you are still having issues you can try and shape the cut off lever, so that moves only as long as it needs to, (up and down quickly-no delay)
Possible Issue 2: Your safety Latch is engaged on Semi Auto mode (Ver. 2 only)
Solution: Where the selector plate is engaging the safety switch, you will need to shave down the knob in a way that the selector plate will not touch the safety lever on semi-auto.
Possible Issue 3: Your cut off lever is too high/thick and cannot let the trolley to cut off properly off of its cut off sear.
Solution: Shave down the protruding mound on the cut of lever screw hole. You should shave it down so that it is completely flush with surrounding edges of the cut off lever. Do not drill too much as the cut off lever will not be able to move freely. The end goal here is to lower the cut off levers position slightly.
Gun Will Not Fire, When Wired Up Fine:

You will notice the electronics of your airsoft gun (wire, trigger switch, MOSFET, motor, etc.) If you can manually fire the gun with the GB open.

What you are most likely dealing with in this case is a simple mechanical problem, not an electrical one. Possible Issue: Your trigger is slipping off of the trigger trolley when you press it in a certain amount. So it essentially slips off and the trolley spring pulls it back to its original position making no contact.
Solution: Add material to the back of the trolley or to the top of the trigger so it will no longer slip off. You will be able to test your modification very easily.
Unexplained- Drop In R.o.F. and Trigger Response:

To further explain this, this will not happen all of the sudden, but gradually over time.

Possible Issue: Your motor brushes need replaced.
Solution: Replace the brushes and clean the motor.
Inconsistent FPS:

Make sure your hop up is set off when troubleshooting here for the initial test, especially with R-Hop and Flat Hop. In addition to preparation, either test with a different chronograph or try another gun on the same chronograph you should be able see if the chrono is or is not the issue.

There really is a lot to be said about this so I cannot cover everything as it would be way too messy.

Possible Issue 1: Too much back and forth play in the hop up unit and the front of the Gearbox shell. When the hop up unit itself moves back and forth about the stationary gearbox shell it will cause inconsistencies in FPS a great deal. * You will be able to notice this when the gun is assembled or mostly assembled.
Solution: Do the O-ring mod. If you have hop spring, they rarely are sufficient enough.
Possible Issue 2: Cylinder Is Not Ported Correctly
Solution: Port your cylinder with your barrel length. There are many tables online. There really is no set formula or ratio for this. The best way of doing this is buying the correct cylinder for your barrel length. If you plan on using heavier BBs such as .28g or heavier, go up one size more. Example, M4 should be ported to a standard ported cylinder if you plan on using heavier rounds, use a type 1 cylinder.
Possible Issue 3: Compression Leak.
Solution: Has already been stated- Refer back to Issue: Lower than expected FPS.
Wind Back Noise After Every Cycle:

You will notice this bizarre noise when you take your finger off the trigger.

Issue: The Anti-Reversal Latch is not engaging the reversal gear on the bevel. When this issue occurs the gears and the motor will torque backwards, this causes a number of issues I will not go into.
Solution: Find out why your reversal latch is not engaging, it could be as simple as the spring has come off or it has broke, the ARL itself has broken, or was installed incorrectly to begin with. If this is not the case, you may need to shim the reversal latch up to better engage with the bevel gear. Modifications such as these are only really pertinent when adding and installing new parts.
Delayed Trigger Response/Trigger Has To Be Pulled all the way For Gun To Begin To Cycle:

Possible Issue 1: Trigger Contacts are Broken or melted:
Solution: Replace trigger contacts or entire trigger switch, both solutions are very cheap.
Possible Issue 2: Female Contacts are too spread out and not making a good solid contact with the sliding male contact.
Solution: Shape optimize the female contacts in your trigger switch so they both make a good solid contact with the male sliding contact.
AEG Works Intermittently:

Meaning it shoots and then goes dead, shoots fine, possibly slows down, and goes dead, the motor may start smoking

Possible Issue 1: Your motor wire(s) keep slipping on and off of your motor terminal(s).
Solution: Secure the wires so they do not move about, if you do not have a version GB, they should almost always be soldered on and then insulated with heat shrink wrap.