Anybody Good With Electronics/Mosfets? New Gearbox from Huang Doesn't Work

[SHÖCK]

I can handle all the mechanical and electrical stuff but my brand new gearbox from Huang doesn't work and it has me totally stumped. Mechanically it is fine, I've cycled it with a motor connected to another trigger. Electrically all the wiring continuity seems to be fine too. The problem is electronic #!%!%
I pull the trigger and nothing happens.

It has this mosfet hardwired into the system though and I'm lost here with how to troubleshoot this and buying a new mosfet and harness after shipping from the only place I've found to carry it (Warstore) will be like 40% of the cost of what the entire gearbox and motor cost me.



Any way for me to test if this is working or not or just burned out somehow? I noticed this design doesn't have a heatsink like older designs had to disipate heat, the whole thing was just covered in shrink wrap. I was thinking of maybe bypassing this PCB entirely so I could have a working gearbox but there are 4 wires coming out of the front of the gearbox and I'm not sure how to connect them up yet.

What does the mosfet really do? It's also connected to the 30A fuse on the same PCB. I figure the mosfet and fuse will help me with overcurrent and proper cycling since I use Lipos.

Here are some related threads I googled showing circuit diagrams of this.

http://forums.airsoftmechanics.com/index.php?topic=1307 (old version)
http://forums.airsoftmechanics.com/i...p?topic=1911.0 (new version scroll down)

[mcguyver]

Most likely the FET is dead. MOSFETs are very sensitive and can die for apparently no reason (even though it may be a spike that was undetected for example).

If you are good with a soldering iron, you can probably replace that FET yourself. If you have access to an electronics supplier like Active Components, they can either get you that exact FET or a replacement from NTE or similar. Probably cost you as high as $25 at worst, but probably less.

[HKGhost]

Top right corner of the FET chip looks fried. Better to just replace the whole board or if you're good with soldering, replace the chip.

[mcguyver]

Originally Posted by HKGhost

Top right corner of the FET chip looks fried. Better to just replace the whole board or if you're good with soldering, replace the chip.

Looks like poor soldering at the shunt wire connection at the source, but there could be a burnt trace underneath it.

[coach]

You could bypass it but you'd have to rewire your mech box to be standard wiring.

[Kos-Mos]

If you have a multimeter, confirm that all traces are good and all resistors are the value they are marked (the little code on them).

The if everything is fine, the FET is probably burnt. Check carefully for a dimple or tiny crack with "oose" on the plastic case of the fet. If there is one, the FET is burnt.

This particular FET has an internal protection diode. That might be blown too (quite stupid to have it inside if you ask me...

Wait... the black wire on the right... it is bypassing the diode... great! there is a protection, but it was bypassed in the circuit.

I sense quite some fail in there...

Can you post a picture of the global circuit, and the other side of the board with what wire go where? Might improve the design while we are at it.

Oh, also, I got a new FET I can send you free, if you feel confident in replacing this one. (the L3803S chip only, that is the actual FET). Vishay's SUM110N03-04P... Will work in there no problem.

[Azathoth]

Originally Posted by mcguyver

Looks like poor soldering at the shunt wire connection at the source, but there could be a burnt trace underneath it.

An iron that was too hot could have also burnt out that chip. Learned that from working on Version 1 Trigger Masters and talking to Don.

You will need to completely de-solder all of the contacts on the switch and redo them to get standard wiring.


I recommend you talk to DonP and get a simple mosfet or get one from ASM You can simply cut the old one off and insert the wires into the proper leads. Is that a 3 wire configuration FET or a 4?

[Kos-Mos]

Originally Posted by Azathoth

An iron that was too hot could have also burnt out that chip. Learned that from working on Version 1 Trigger Masters and talking to Don.

You will need to completely de-solder all of the contacts on the switch and redo them to get standard wiring.


I recommend you talk to DonP and get a simple mosfet or get one from ASM You can simply cut the old one off and insert the wires into the proper leads. Is that a 3 wire configuration FET or a 4?

From the picture, I would way 3 wire (M+, M-, T). M+ is connected directly to B+ and the trigger. M- goes though the FET and then to B-. T is connected to the trigger.

A normal AEG will be M+ to T. B+ to T. B- to M-.

The way your FET unit is built, the easiest solution is to get a new trigger unit already wired.

[Azathoth]

I agree with the above. No Mosfet aside from the systema one is 3 wire configuration. and those are terrible fets.

[mcguyver]

Originally Posted by Azathoth

I agree with the above. No Mosfet aside from the systema one is 3 wire configuration. and those are terrible fets.

The FET pictured above is a 3-wire. What appears to be a center pin is actually not used. The source is the heatsink mounted to the board.

[SHÖCK]

Originally Posted by Kos-Mos

If you have a multimeter, confirm that all traces are good and all resistors are the value they are marked (the little code on them).

The if everything is fine, the FET is probably burnt. Check carefully for a dimple or tiny crack with "oose" on the plastic case of the fet. If there is one, the FET is burnt.

This particular FET has an internal protection diode. That might be blown too (quite stupid to have it inside if you ask me...

Wait... the black wire on the right... it is bypassing the diode... great! there is a protection, but it was bypassed in the circuit.

I sense quite some fail in there...

Can you post a picture of the global circuit, and the other side of the board with what wire go where? Might improve the design while we are at it.

Oh, also, I got a new FET I can send you free, if you feel confident in replacing this one. (the L3803S chip only, that is the actual FET). Vishay's SUM110N03-04P... Will work in there no problem.

Thanks, I going to borrow a better multimeter than the one I have and check the continuity of the actual board soon. Also the picture I posted was taken from the forums I linked as an example of the same unit I have but it is not actually a picture of mine. I haven't removed the heatshrink from my board because I was waiting for a reply from Huang about a replacement unit but I can post some high-res pictures of both sides of the board and the global circuit pretty soon.

I can probably get someone with a professional soldering station at his workplace to help me with removing and replacing the FET which is awesome if have a new FET for me. That's very much appreciated and very generous of you.

You guys are awesome. I'm glad that there are such knowledgeble people on here.

[Kos-Mos]

You don't need a soldering station. In fact, if you use one imporperly you will probably set the temperature too high or too low.

I am using a plain old 60W adjustable iron. Set it at 30W and let it heat up enough to instantly melt the tin you put on it, but before it does the little fizzle and smoke.

Take you time, make sure not to lift the traces (if pull before the tin is melted).

You then want to make sure that the traced where you put the new FET are clean. Board cleaner and a desoldering braid is perfect.

And a tiny amount of new tin to each contact (not enough for it to bubble).

Then place the FET at the right spot and hold it firmly in place. I am using a pair of "3rd hands" to hold the board flat to my workbench, then a pair of heavy long-noze pliers to put pressure on the FET and keep it there.

Then you put a bit of tin on your iron (to give a good contact for heat transfer) and press the back tab of the FET against the board. It will melt the pre-tin on the FET then the little amount of tin on the board.

As soon as you feel it moved and stopped, remove the iron but leave the pliers there. Depending on what tin you are using, it can take up to 3 seconds for it to harden.

Then repeat with the two legs. You don't have to leave the pliers there, the joint on the back tab will hold it in place if you don't overheat the FET.

PM me your adress. I will send you some FETs.

[Spawn28]

Have you tried contacting Huang maybey he will send you a new one or at least help ya out with a new Mosfet just an idea couldnt hurt to ask was it DOA or did you fry it?

[juicy]

I suck with electronics - I'm being honest here.

The JG mosfet unit in my HK416 has possibly died. Skladfin's had two of them and his first one burnt out extremely quickly. Experience seems to be suggesting that the JG mosfet just isn't that durable at all?

[Kos-Mos]

From the specs of the stock FET and the fact that the internal protection is shorted and the fact that other than the fuse there is no protection....

Theses can fry quite easy, yes.

Removing the bypass and using a better FET (Just ordered some new Vishay 290A units... the stock one on theses is rated 90A) probably will help incredibly.