fet modding disaster

[klims]

i bought a bunch of the fet’s available on ausmicro and am trying to do an fet upgrade to my iwaver monster truck. i had no problems with making the stack or soldering it on, however i ran into trouble when i turned the power on. i didnt have the motor terminals connected, but what happened was the steering jerked over to one side and stayed there twitching in the turned position. since i didnt really know which way the fet stack should be pointing, i justed picked a direction (dot on the same side as the stock fet) and hoped for the best. i thought the direction might have been a problem, but i then realised that in the process of soldering and what not, i tore the steering wires out or their positions and now have no idea where they were. i was hoping that someone might be able to send me a picture of what it should look like so i can fix it all up. and another thing i seem to have done in my crazyness of removing the fets was bridge three ternimals on one side of the fet! i have included a photo (not very good) of the board and i have highlighted the terminals that i managed to bridge. i have been trying to use solder wick to unbridge it, but thats the way i got the third terminal bridged into the other two in the first place! can anyone please offer me some advise on how to fix this mess that i have created? thanks[ATTACH]198[/ATTACH]

[betty.k]

this thread should help with the steering:
http://www.ausmicro.com/forum/showthread.php?t=14131

bridging the pins on the motor terminal side of the fets is ok, if you notice they all solder to the same pad on the pcb. just don’t bridge the other side. :8ball:

[klims]

PHEW!!!!!! thats a relief. because i was looking at the bridge and it would seem that it is in the deeper layers of the board, which would mean that i had only melted the top layer green stuff to reveal the bridge. just one more question, what does that dot on my fet mean and which side should it be on? thanks for your help once again betty.k!

[merc-blue]

The dot indicates pin one it should be in the same spot as the origional which is facing away form the motor/battery terminal

[Aaron]

Yeah on the motor terminal side I remove the solder resist (green stuff) between the pins. Then when soldering the stacks up I bridge them in two solid columns per stack – some people bridge all 4 pins bit that’s over kill. It gives a slight heatsink effect, adds mechanical strength and is easier than doing another 8 single pin strips (which you must do on the other side).

A.

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Site Owner Guy.

[Aaron]

I’m doing a customer stack tomorrow so will snap some pics and post 🙂

A.

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Site Owner Guy.

[Dangerous Dave]

speaking of FET mods, the Codesuidae page for the ZZMT mod has a big error in it. Instructs you to remove Q9 and Q10, but should be Q5 and Q6.

9 and 10 are the steering transistors!

[klims]

thanks for all the info guys. im still having trouble understanding which side the dot should be on, so i have edited the picture i put up with a red arrow showing the spot where the dot is. my issue is that the original fet had the dot in the middle of the fet but toward one side, not in a corner like the new ones. from what aaron said about it facing away from the motor terminals, would it be safe to say that i am wrong?

[betty.k]

the red dots in this pic indicate where the fet dots should be :8ball:

[klims]

thanks for that. i might just have a play around with the steering wires. the ones on my board are all on the right hand side, but i guess since the red and balck are together thats a start!

[klims]

on another note does anyone know how robust these little fets are? when soldering them with my trusty $7 warehouse soldering iron i was wondering if i could possible be cooking them. does anyone have any experience with this?

[klims]

HAHAHAHAHAHAHAHAHAHA you guys are gonna laugh so badly when you find out why it wasnt working. being the 3rd year engineering student that i am with no practical experience, i forgot to plug in the frequency crystal when testing, and so was getting no response from my remote control. what an idot!

[betty.k]

:smiley8: :8ball:

[klims]

yeah its a bit like that. i also just installed a spider in my mr02. for anyone who is a newbie to this like me, i suggest you are very careful when soldering the green wire to the tab. while i was doing mine the tab came unstuck from the board and broke off, only leaving the mircoscopic track behind which is covered by the green stuff. let me just say that its not the position you want to be in. anywho it was well worth the effort. i cant belive the performance! thanks for all the help guys

[Admin]

klims wrote:

…i also just installed a spider in my mr02. for anyone who is a newbie to this like me, i suggest you are very careful when soldering the green wire to the tab. while i was doing mine the tab came unstuck from the board and broke off, only leaving the mircoscopic track behind which is covered by the green stuff. let me just say that its not the position you want to be in…

That’s for sure! That’s why it’s good to use a nice hot iron and work quickly…you either overheated the board and therefore delaminated the solder pad or pulled a bit too hard on the wires when the solder wasn’t molten yet. Been there, done that! 😀

[ph2t]

another reason why I CUT the mosfets off with a stanley/hobby knife before doing anything. this way the net overall time that the pads hace been exposed to heat is less…..

[Author]

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