# Auto firing Mech Mod.



## Chickenstrip (22/2/20)

Hello, I'm having an issue lately.

I've had my mech mod as long as I can remember. In fact, over the years I've had many of them. I've only got one left now which I use mainly as a priming device for my billet box. Never had an issue with it. 

I recently made a trade with a friend. I got an old MTL RTA 

All was well for a few weeks. But now I'm having the mech autofire on me around 1-3 times a day. And I cant understand why. Let's set the stage:

Basic hybrid mech tube.
25R battery. Perfectly wrapped.
MTL tank drawing ~5amps.
510 pin protrudes plenty.
My button is not assembled incorrectly.
I've checked that the cause is not due to the coil shorting on the inside of the tank.
I always put my battery in the correct way so that it completes the circuit rather than dead shorting when something like this happens. 

What else could it be? It's not really a major issue in that it's highly unlikely it will explode. It's way below the CDR of the battery. (+-15-25% of CDR) depending on battery level. I never leave the battery in the mech or leave it unattended. 

But it's really annoying because usually by the time I've got the battery out. My cotton is cooked.

Anyone got any suggestions?


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## Grand Guru (22/2/20)

I’m no expert in mech mods but my logic says it might be the button spring throw has become smaller with time and may need replacement.

Reactions: Like 2 | Agree 2


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## Chickenstrip (22/2/20)

Grand Guru said:


> I’m no expert in mech mods but my logic says it might be the button spring throw has become smaller with time and may need replacement.




Good call, let me check that out!

Spring looked alright but has now been replaced. Will monitor for the moment.

Reactions: Like 2


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## JPDrag&Drop (22/2/20)

Clean the area where the spring is as vapor can seep in and check if the spring is still good.
Get some mechanical lube so everything can function smoothly.

my mechs is cleaned out once a week. Even when it’s not used as mechs should not be used if not cleaned properly.
If the button is not smooth when pushing. Then give it another clean coz the eye can’t see everything.
A clean mech is a safer mech

Reactions: Like 2 | Agree 1


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## Chickenstrip (22/2/20)

JPDrag&Drop said:


> Clean the area where the spring is as vapor can seep in and check if the spring is still good.
> Get some mechanical lube so everything can function smoothly.
> 
> my mechs is cleaned out once a week. Even when it’s not used as mechs should not be used if not cleaned properly.
> ...




It's a stainless tube. Just cleaned the button when I replaced the spring. But it was already clean. Definitely not a cleanliness issue . I'll have to monitor to see if the spring was the issue but I'm starting to suspect the RTA.

Reactions: Like 2


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## Puff the Magic Dragon (22/2/20)

Does the RTA work on another device ?

Reactions: Like 2 | Agree 1


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## Resistance (22/2/20)

It can't be the RTA. The circuit needs to be complete in order for current to pass to the RTA.
Something on you mech is causing this. Take out the battery and check the inside wall of the mech if it a tube mod.
If it's a box mod you should be able to see whats shorting.

Reactions: Like 1


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## Chickenstrip (23/2/20)

I haven't had another issue since the spring was replaced with a stiffer and longer one. So far so good. Thanks so much guys. I'll have to report back in as soon as something happens.

Reactions: Like 3


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## Resistance (23/2/20)

Chickenstrip said:


> I haven't had another issue since the spring was replaced with a stiffer and longer one. So far so good. Thanks so much guys. I'll have to report back in as soon as something happens.


I think that could solve your issue ,but still keep an eye like you said.

Reactions: Like 1


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## Chickenstrip (24/2/20)

Got a bad short this evening. Sigh. Will teardown on the weekend thanks for the assistance everyone! More grateful than I can express.

Reactions: Like 2


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## Adephi (24/2/20)

Maybe strip the RTA completely down and check that the peek insulators are still good. 

I know its very unlikely but its worth a shot.

Reactions: Like 1 | Thanks 1


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## Chickenstrip (24/2/20)

Bad news, not the spring. Thanks @Adephi for the idea. I'll try it out.

Reactions: Like 1


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## Resistance (24/2/20)

Chickenstrip said:


> Bad news, not the spring. Thanks @Adephi for the idea. I'll try it out.


What's your battery orientation? +Up or down?

Reactions: Like 1


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## Chickenstrip (24/2/20)

Resistance said:


> What's your battery orientation? +Up or down?



Positive up. I may be a little slow but I'm not brain dead

Reactions: Winner 1


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## Chickenstrip (24/2/20)

I'm pretty sure it's got something to do with the button. @Resistance , your post regarding the circuit completion makes a lot of sense. I'm going to muck about with the switch because if I take a moment to think about it... There really is no other realistic reason for it to complete the circuit. I'm going to open it up. Re clean and put in a different size spring and troubleshoot from there.

Reactions: Like 1


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## Resistance (24/2/20)

Chickenstrip said:


> View attachment 190825
> 
> 
> Positive up. I may be a little slow but I'm not brain dead


Trying to figure out why it's auto firing.
Because if it was the other way around it would have blown already

Reactions: Agree 1


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## Resistance (24/2/20)

Chickenstrip said:


> I'm pretty sure it's got something to do with the button. @Resistance , your post regarding the circuit completion makes a lot of sense. I'm going to muck about with the switch because if I take a moment to think about it... There really is no other realistic reason for it to complete the circuit. I'm going to open it up. Re clean and put in a different size spring and troubleshoot from there.


Maybe also check the insulator on the switch.

Reactions: Like 1


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## Chickenstrip (24/2/20)

Resistance said:


> Maybe also check the insulator on the switch.


Switch has no insulator but I can easily make one.

Reactions: Like 1


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## Resistance (24/2/20)

Chickenstrip said:


> Switch has no insulator but I can easily make one.


Either that or something is shorting through your battery wrap.

Reactions: Agree 1 | Winner 1


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## Resistance (24/2/20)

Post pics of the switch bro. Also check the inside of the mod

Reactions: Like 1


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## Chickenstrip (26/2/20)

Will do when I've got some time. My curr


Resistance said:


> Post pics of the switch bro. Also check the inside of the mod


Current work load gives me less than an hour of personal time per day. Wraps are good as the problem persists with any battery. And I'm religious with properly wrapped batts. The odd thing is that this mech has place for am insulator but is not shipped with one. What's more odd is that the issue never arose in over 4 years. It's just recently. This weekend down I'll do a total teardown. Rewrap and and an insulator. I'll fit a new spring and tear down the atty too. I'm sure I can work it out. My thread was basically created to help me narrow down the problem based on anyone elses experiences. But looks like I'll have to put my mech-anich gear on and investigate in full. Will report back with diagnostic results asap.

Reactions: Agree 1


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## Resistance (26/2/20)

Do you have a multimeter?


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## RayDeny (26/2/20)

What Mech is it? If we knew the construction of the tube and button we could assist more. 

the only real common denominator with the bat positive up would be the switch.

Reactions: Like 1 | Agree 1


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## Resistance (26/2/20)

RayDeny said:


> What Mech is it? If we knew the construction of the tube and button we could assist more.
> 
> the only real common denominator with the bat positive up would be the switch.


Agree, then we wouldn't be asking all these silly questions that can make either party look foolish
Post a pic @Chickenstrip .we just want to help

Reactions: Like 1


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## Chickenstrip (27/2/20)

Okay so I've realised why it's happening. 

The button doesn't have an insulator. It relies entirely on the battery's wrap (the overlap on the negative side) to prevent the negative from making contact with the button and subsequently the mech tube which prevents the circuit from completing. 

So, the connection/autofire was A - intermittent. And, B - usually after I knock or put the mech down and it hits the table with a bit of force.

As mentioned I like to keep my batteries freshly wrapped. Turns out, this contributed to the problem. You see, aftermarket wraps are somewhat thinner than original wraps, at least the ones I've got are. Also, the wraps need to be fitted so that a significant portion of the negative end of the battery is covered. Apparently, I wrapped them a little short of the ideal position.

The combination of the (give or take) 1-2mm
Short negative wrap overlap. Combined with the thinner wraps is what caused the issue. 

Because the wraps didn't cover "enough" of the negative end of the cell, it meant that the cells point of electrical contact was notably closer to the button, albeit not much, but enough to be a factor.

As mentioned before, the wraps are not much thinner but notably thinner and again, enough to be a factor. Which meant the battery had ever so slight play inside the tube.

If one of those "issues" happened without the other, there would be no problem. But because both of the "issues" were combined what would happen when the mech would take a knock, a bump, a little momentum from basically any kind movement , the battery would move (due to play caused by thinner wraps) when the battery moved within the tube it would push itself closer to the wall of the tube. Since the contact break relies entirely on the wrap, the insufficient coverage of the wrap on the negative end of the cell combined with the battery play, caused the battery to shift far enough for the exposed negative part of the cell to make contact with the button wall, completing the circuit and causing the device to fire.

I hope this makes sense. I feel like I over complicated the explanation in way that makes me seem pretentious but after typing all that I can't be bothered to re-type. 

My solution was: 

Replace the spring with a stiff spring that has more distance and resistance.

Rewrap the battery with a thicker wrap.

Ensure that the new wrap has adequate protection for the negative end of the battery.

Create and fit an insulator for extra protection.
I will remove the insulator and spray paint the inner side of the button (except for the contact pin) to achieve the same insulation result as this will mean less maintenance when changing batteries.



I'd like to give a seriously sincere thanks to everyone who contributed to this thread. Initially I had no idea where to look for the issue and a lot of the information shared not only guided me but made me realise that there is clearly a logical way to diagnose the problem.

Apologies for not posting photos, as mentioned, I get very little free time. 

I won't post photos now since the issue is resolved but for the sake of science the mech in question is a SMPL

Reactions: Like 3 | Winner 1


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## Resistance (27/2/20)

Chickenstrip said:


> Okay so I've realised why it's happening.
> 
> The button doesn't have an insulator. It relies entirely on the battery's wrap (the overlap on the negative side) to prevent the negative from making contact with the button and subsequently the mech tube which prevents the circuit from completing.
> 
> ...



Sand the surface a little and use enamel paint, other than that.well done glad you got it figured out.

Reactions: Thanks 1


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## Chickenstrip (27/2/20)

Resistance said:


> Sand the surface a little and use enamel paint, other than that.well done glad you got it figured out.



Spray Painting is a personal passion of mine. I hear you. I will absolutely do that. Appreciate your help. 

Got something I want to discuss with you personally. I'll drop you a PM sometime this week to explain and exchange expertise. I've followed your DIY mod threads and I reckon you're the man to talk to. Shot for all above brother. You're a really helpful and knowledgeable member. I take your advice as an immediate first step with regards to modifications and repairs. Off to bed. Early morning. Peace brother

Reactions: Winner 1


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## RayDeny (27/2/20)

That’s awesome, great catch on that one.

Reactions: Agree 1


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