My AEG won't fire anymore: a step-by-step diagnostic flow

My AEG won't fire anymore: a step-by-step diagnostic flow

you pull the trigger and nothing happens. or it makes a noise but no BB comes out. before you crack the gearbox open, work through this flow from top to bottom. in the vast majority of cases the problem sits in the first three steps, and those need no tools.

important first: pull the battery and pull the magazine before you touch anything. an AEG that "does nothing" can still have a BB in the chamber.

let me sort this out quickly, because an airsoft aeg not firing is really three different problems:

• A. nothing at all. no sound, no movement. go to step 1
• B. motor spins or makes noise, but no BB. go to step 6
• C. air comes out but no BB, or BBs just roll out. go to step 8

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A. nothing at all

step 1: the battery

yeah, i know. and yet this is the answer in half the cases.

• is the connector actually seated? both halves, all the way?
• is the battery charged? measure it. a 7.4 V LiPo should read above 7.4 V, an 11.1 V above 11.1 V
• is a cell dead? check per cell with a cell checker
• try another battery that you know for sure is good

if it works with another battery: your old pack is done. a LiPo that has been deeply discharged is not something you charge back up. see my piece on LiPos.

step 2: the fuse

most AEGs have a fuse, usually in the battery compartment or in the handguard, sometimes in a small plastic housing in the wiring.

• take it out and see if the little wire inside is still intact
• if in doubt: check continuity with a multimeter
• replace with the same rating. often 15 A, sometimes 20 A. don't put a heavier one in and don't bridge it with a piece of wire

if your fuse blows, that is a symptom, not a cause. something is drawing too much current. if it blows again right after replacing it: something is jammed in the gearbox or you have a short.

some AEGs have no fuse. then you skip this step.

step 3: wiring and connectors

• gently tug the wires at the connector. any movement? a broken wire inside the insulation is not visible
• look for scorched or melted insulation
• with a crane stock or a replica with wiring running through the buffer tube: those wires take a beating when you fold the stock in and out. classic spot for a break
• is there a pinched wire between the gearbox and the shell?

step 4: the trigger contacts

if you don't want to open the gearbox: on many replicas you can open the motor grip and pull the motor, then you can see the underside of the gearbox.

often the problem is simply dirt and oxidation on the trigger contacts. that happens especially if you run 11.1 V without a MOSFET.

• pull the trigger firmly a bunch of times, sometimes you scrub through it yourself
• if you have access: clean the contacts carefully with contact cleaner and a bit of fine sandpaper or a glass fibre pen
• if the contacts are badly burnt or deformed, they need replacing

symptom that points here: it works sometimes and not others, or only when you pull the trigger really far.

step 5: the motor

• take the motor out (unscrew the grip plate at the bottom of the grip)
• connect the battery straight to the motor, very briefly. does it spin? then the motor is fine and the problem is in the wiring or the gearbox
• doesn't spin: motor is dead, or the tabs are loose
• look at the pinion gear on top of the motor. are the teeth worn down or rounded off?

if the motor spins freely on its own but not in the replica, and the wiring is fine, then your gearbox is probably jammed (see step 7).

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B. it makes noise but nothing comes out

step 6: listen, what exactly do you hear

this is diagnosis by ear and it works surprisingly well.

clicking or rattling, motor keeps spinning. very likely a stripped piston. the piston teeth no longer grab the sector gear. see my separate piece on that clicking sound, it explains how to tell a stripped piston, stripped gears and wrong motor height apart.

one hard slap and then a dead stop. possibly a broken tooth or a blockage.

buzzing without movement. the motor gets current but can't turn the gearbox. blockage, or a spring too strong for the motor when the battery is low.

high whining sound. bad shimming or wrong motor height. still works, but it's eating itself.

normal sound, but no BB. go on to step 8.

step 7: gearbox jammed

if nothing turns and the motor is fine:

• take the motor out and turn the pinion by hand. does it run?
• with the motor out, stick a long allen key through the motor hole to turn the bevel gear. is it stuck?
• often there's a broken piece of piston, a BB or a snapped-off tooth wedged between the gears

at this point the gearbox has to come open. if you have never done that: get it done, or first find a good video guide for your specific gearbox version (V2 and V3 differ quite a bit). there's a tensioned spring in there and the anti-reversal latch jumps out if you're not paying attention.

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C. air yes, BB no

step 8: magazine and feeding

the most common problem, and the least serious.

• try another magazine. sounds dumb, works often
• with midcaps: is it wound? midcaps have a spring you have to tension
• with hicaps: did you turn the wheel?
• are the BBs stuck? shake the magazine
• look in the magwell for a jammed BB
• is the feeding lip damaged?

trying a different weight or a different brand of BB can help too. some magazines are picky.

step 9: the hop-up

• is your hop-up dialled all the way in? a fully closed hop clamps the BB tight in the barrel
• is the hop arm still seated properly? when you take it apart the nub sometimes pops out
• is the bucking crooked or torn?
• is there a BB jammed in the hop-up unit?

dial your hop fully open, pull the magazine, and fire a few times. does a BB that was still in there come out now?

step 10: nozzle and tappet plate

if air comes out but the BB isn't fed, the tappet plate is a suspect. it pulls the nozzle back so a BB can drop into the chamber.

• a broken tappet plate is a classic. the little lip snaps off
• a worn or broken tappet plate spring gives the same picture
• a broken air nozzle too

symptom: normal sound, some air, no or irregular BB feeding. this needs the gearbox open.

step 11: compression

if a BB does come out but far too weak:

• piston head O-ring worn
• cylinder head O-ring worn
• crack in the cylinder
• nozzle O-ring worn
• broken spring (then it's really weak)

weak compression shows up on the chrono. if you used to shoot 1.15 J and now get 0.7 J, this is your direction.

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quick reference table

when to stop and get it done

i'm not shy about wrenching on my own gear, but if you run into the following and you have never done it before:

• the gearbox has to come open and you don't know which version you have
• something needs soldering on the motor or a MOSFET
• there are metal particles in the gearbox (then everything comes out and gets cleaned)
• the cylinder or gearbox shell is cracked

at pretty much every field there's someone who'll do this for a few bucks and a beer. that's cheaper than having to repair it twice.

prevention

most of these faults announce themselves. a short routine after every game day catches a lot of them: battery on storage voltage, clean the barrel, check the hop, and just listen whether the sound is still normal. i have a separate piece on that.

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Also on Airsoft-FOB

• also available in dutch: Mijn AEG schiet niet meer: diagnoseschema stap voor stap