Featured Help figuring out g&g prk9 mosfet issue

Discussion in 'Gun Building, Modifications & Repairs' started by Mike223, Nov 24, 2021.

  1. Mike223

    Mike223 Member

    56
    10
    Stacy
    Hello,
    I am having issues with a g&g prk9 and its related to the mosfet. It does a cycle of sometimes firing once, then a two round burst other times and back to once and so on beeping in between trigger pulls. This happens in both semi auto and full auto. I have seen a manual for a g&g mosfet mentioning make sure the battery is charged and also that it may be a sector gear out of place or something like that if the light on the mosfet is on. Also the seller mentioned trying to reset it but I dont know how and I dont have a tool to program it. Would I need a mosfet programming tool to fix this issue?

    https://imgur.com/a/2TsaZHf

    I just charged one and it did the same thing. Otherwise id have to take some of the gun apart to take a look at the mosfet. I have essentially no experience working on airsoft gun so im worried ill end up breaking it and it not working once I put it back together.

    If its too much of a hassle I can always ask the person I bought it for, for a refund on paypal. One more thing thats wrong with it is the battery hatch doesnt wanna latch, unless I fiddle around with it for a minute or so. Something I was not aware of when I bought it, same with this firing issue but this part may be easily fixed idk.

    I contacted him and he told me to take out the charging rod to see if its bent. I did and it looked very slightly bent at the end. Could this be enough to make the hatch not work properly? Its not a very noticeable bend in the rod.

    Any advice on what is wrong with it? And should I think about returning it and getting my money back? I feel like I got it for a decent price but I wasn't planning on paying for a misfunctioning battery hatch and possibly mosfet as well.
     
  2. Guges Mk3

    Guges Mk3 Administrator Staff Member Administrator Supporting Member Lifetime Supporter

    8,428
    4,741
    Minneapolis
    You battery can be bad. What kind of battery are you using?
     
    wetpee likes this.

  3. Mike223

    Mike223 Member

    56
    10
    Stacy
    I have 3 of them, im using a nastima 1200 mah 11.1v lipo 20c.
     
  4. Guges Mk3

    Guges Mk3 Administrator Staff Member Administrator Supporting Member Lifetime Supporter

    8,428
    4,741
    Minneapolis
    And what is the output voltage?

    Pack isn't a very good one, sadly...
     
  5. Mike223

    Mike223 Member

    56
    10
    Stacy
    How do I know the output voltage? Is there an equation or do I need to plug it up to something? And what makes it not a good pack? What do you recommend?
     
  6. Ben3721

    Ben3721 Well-Known Member

    749
    386
    I've fixed this issue 3 times this year. At least the v2 type. Id imagine they are basically the same tho.

    This issue is common among the older and newer generation of g&g trigger switch boards. The microswitches become crushed from the trigger and start acting faulty half the time due to crush damage.

    To fix this issue you must replace the selector plate, trigger on the later designs - which they tried to change the trigger to a proprietary one that has a leaf spring to fix the issue, and obviously replace the contact board with a board mosfet or contacts.

    I generally enjoy teching, but when I see something so petty like this so often it gets annoying to fix.

    I actually still have all the g&g mosfets and trigger boards if anyone wants photos of them. One I took apart the contacts to see how it ruined them physically however. The plastic top that presses the metal button was flattened to the point it wouldn't activate.
     
    OutlawAirsoft, wetpee and aotsukisho like this.
  7. Mike223

    Mike223 Member

    56
    10
    Stacy
    It sounds like it might be more trouble than its worth lol, I might just ask for a refund at this point as I didnt know about this as he said it worked fine, unless it somehow got damaged during shipping idk. Also seeing as I have basically no experience there might be an easier gun to work on.
     
  8. Mike223

    Mike223 Member

    56
    10
    Stacy
    Also would you happen to know if the G&G TR16 MBR308SR would have the same issue down the road? I figure it might since its a g&g, and im just curious since I have one.
     
  9. Guges Mk3

    Guges Mk3 Administrator Staff Member Administrator Supporting Member Lifetime Supporter

    8,428
    4,741
    Minneapolis
    If you run LIPO you need a LIPO cell checker. It tells you the condition of each cell and pack as a whole.

    [​IMG]
     
  10. aotsukisho

    aotsukisho Well-Known Member

    797
    442
    Yes please
     
    Ben3721 likes this.
  11. Ben3721

    Ben3721 Well-Known Member

    749
    386
    I have another g&g hitting the table Friday too, I'll be checking over it over the weekend to find the point of failure. Likely same thing.

    I'll post a thread with all the juicy photos. And video of the "malfunction" that this thread most likely describes.


    The silly thing is the newer generation mosfet boards put like a leaf spring onto the trigger so even if you pulled the trigger all the way hard should "in theory" not crush and ruin it.

    Unfortunately they must have skipped on testing it with a bag of bbs. Heck the one I just had failed in under 1000 shots. Which is absolutely embarrassing for a manufacturer.

    The design of the mosfet with all the electronic chips being external and all the switches being internal with a half dozen extra wires to all the sensors was a poor design to begin with. Darn wires catch the motor pinion half the time, which most the time can damage them.
     
    aotsukisho and wetpee like this.
  12. Mike223

    Mike223 Member

    56
    10
    Stacy
    If I got this battery charger/ balancer would this be able to do that?

    https://hobbyking.com/en_us/imax-b6...D=45235&indexName=hbk_live_products_analytics

    And could I have this plugged into the battery while it’s in the gun if I have enough room in the compartment so I don’t drain the battery too low? Or do I not need that?

    https://www.amazon.com/Battery-Moni...ocphy=9019524&hvtargid=pla-304998738630&psc=1
     
    wetpee likes this.
  13. Mike223

    Mike223 Member

    56
    10
    Stacy
    If I did those things would I no longer have to worry about crushing the switches? Or would it just end up possibly happening again in the future?

    Sorry if this is a dumb question I just have very little knowledge about the internals of airsoft guns at the moment.
     
    wetpee likes this.
  14. Mike223

    Mike223 Member

    56
    10
    Stacy
    Also the seller said he had an old g&g l85 that would get stuck doing full auto and he said the only way around it was to reset it with an etu control card or replace the mosfet with a different one, which is what he did.
     
    Last edited: Nov 25, 2021
  15. Ben3721

    Ben3721 Well-Known Member

    749
    386
    Well, another alternative is fixing the microswitch with a new one.

    If you don't have experience with aegs, including ak style v3 gearboxes then you'd need to find a tech with experience with aks. I've only opened the m4 g&gs, not ak's. I'm not sure if the ak variant is the same process or if it's proprietary.

    My guess is it's the same deal as the m4 types.
     
  16. wetpee

    wetpee Active Member

    194
    77
    Chicago
    I would love to see photos of this. Haven't gotten any of these in myself. Luckily, G&Gs aren't so popular in my area.
    No such thing as a dumb question my man. Ask away.
    Through my experience, 1. the 11.1V is probably too much for the specs of the gun and its overspinning, although I'm not familiar with the cutoff mechanism in these guns. Sounds like it may not be a traditional design. 2. Your LiPo may be going bad which would be a result of insufficient Amp supply for whatever replicas you've been using them in. This is a common fault with what retailers and manufacturers recommend. You should absolutely be prioritizing mAh and C-rating over voltage. It will run a little slower in many applications, but it will be healthier for the motor and batteries. 3. I personally feel this should not be a switch or MOSFET issue, but it definitely could be and sounds like Ben has some experience with this particular issue in similar models. If this is the issue or one of the issues, that is truly poor design and/or manufacturing.
     
    Last edited: Nov 25, 2021
  17. Mike223

    Mike223 Member

    56
    10
    Stacy
    I got three used batteries along with a kwa I bought a while ago so I didn’t pick these out. A unrelated side note but I think that gun was not lipo ready as it was stock with no mosfet so he was using an 11.1 in the gun I have now that probably wasn’t built for it. I would’ve tried my other battery which is a 8.4v but it’s tamiya connected and the gun is deans.

    If it was up to me and I was buying a new battery I’d be ok with getting a 7.4 lipo as I don’t need a bullet hose or anything special.

    Do you have any recommendations on a minimum c rating and mag I should be getting? I’ve heard somewhere 15 is not very good 20 is better 25 I would assume is even better but I’m sure there’s a cutoff as you go up it’s not useful or makes something worse.

    Also I don’t know if it can even house a 11.1 as the battery compartment is not very big, the previous owner used a 7.4 I believe and he said it was a tight squeeze.

    Yeah at this point I just wanna get rid of both my g&g guns and run as far away as I can lol. If this is gonna be an issue as I’d rather not deal with it and I don’t absolutely need a adjustable mosfet, and if I did I might just go with a different brand or something down the road.
     
  18. wetpee

    wetpee Active Member

    194
    77
    Chicago
    This is a fallacious term. It means next to nothing. Even having a MOSFET doesn't make something "LiPo ready". You could run a massive high mAh, high c-rating 7.4V in something with no MOSFET for a very long time but an 11.1V low mAh, low discharge LiPo will kill it in 15k rounds. If it doesn't have a MOSFET installed, it likely has a weak motor, weak spring, and a "high torque" forgiving gear ratio so the machine doesn't demand many amps to run. Voltage simply makes things run harder. If the gears, gearbox, or bushings are manufactured poorly, gears are shimmed poorly, or myriad other variables that determine load, load capacity, and efficiency of the system, running a higher voltage battery is simply spelling a quicker death for the machine whether it has a MOSFET to protect the trigger contacts or not. In the past, Li-Po ready meant having bearings or something stupid. They just continue to move the goal post or come up with new terms as consumers become more informed. I always recommend people use less than 11.1V batteries unless (on top of having a proper MOSFET) they have opened up their gearbox and confidently confirmed smooth operation of the drivetrain or they have reshimmed it and are confident enough to say it is better than it was from factory.
    Amp output = C-rating * Ah
    So, 1100 mAh @ 20C (continuous) = 22A (continuous).. burst output is probably good up to like 40A, which is a burst of current that happens in milliseconds.
    This is just barely sufficient for most stock AEGs. Do not be fooled by Titan batteries or other Li-Ion batteries. They are far inferior to LiPos. They max at at like 6C continuous.
    Didn't you say you installed a titan in the MBR in your other post? If so, then you shouldn't have anything to worry about with that one, assuming good shimming of the gears has been confirmed, and everything was reassembled properly. The rest of the internals are very high quality. The PRK is a cool replica, but I am not familiar with the internal parts set on those. G&G's "premium" offerings tend to have very solid internals, aside from the MOSFETs and their accompanying trigger control solutions. I can guess that at least the motor and gears are desirable. If you're more concerned about bang for buck though, PRK9 is a questionable buy. You could have scooped an Arcturus or LCT and be much better off. Both have pros and cons vs each other and G&G, but both are brands more focused on AKs and the V3 gearbox, and they do those quite well.
     
    Last edited: Nov 25, 2021
  19. Mike223

    Mike223 Member

    56
    10
    Stacy
    It probably is a good idea to start opening up the gearboxes and being able to do shimming and all that.

    As for the battery I’ll probably get a 7.4 lipo with a higher mah and maybe even a tad higher c rating as well. Or a 9.6 nimh but I hear lipos are preferred.

    the previous owner had a tech install it, so yes it does have the gate titan in it.

    I was just worried about how a tech said in this thread that some mosfet boards can be crushed by the trigger and he’s seen it in g&gs before.

    Idk if he means the way their specific mosfets are built or the problem would be solved simply just using another mosfet not made by g&g. Or if the issue is with the g&g guns and it doesn’t matter what mosfet you use it will happen.

    As for the questionable buy that might be true haha. I bought it because he was selling it a bit cheaper than what I would imagine someone would sell it for so I figured why not. Similar to my other guns I get it cheaper new than used but I’m gambling with whatever damage they did to it lol. Anyways in my defense what I bought would be cheaper in my situation lol, but I still get what you mean.
     
    Last edited: Nov 25, 2021
  20. Ben3721

    Ben3721 Well-Known Member

    749
    386
    Wait does the g&g aeg in question have a gate titan installed?

    The higher end internal mosfets use optical sensors or even magnetic. They don't have micro switches as a failure point like the g&g mosfets do.