Messed up MOSFET mod

clxfiles · Post by **clxfiles** » Tue Feb 21, 2006 10:59 pm

I tried to fet mod a zz but now I get no power to the motor. Steering still works, just not the fwd or back. Below are some pics or if they're not working, links to pics that show what I did.
Basically I took ZZ that uA modded for me a while back and tried to copy it. His is the one with the black paint on it. For the small wires to jump the gates I used the small wires that were in CAT5 twisted pair.

http://photobucket.com/albums/e81/clxfi ... =ZZTOP.jpg

http://photobucket.com/albums/e81/clxfi ... Bottom.jpg

So all I did was swap the 4 transistors for for 2502 fets and used the copper wire to "jump" those gates. Was there something else I was supposed to do?

SHAUN · Post by **SHAUN** » Tue Feb 21, 2006 11:03 pm

Pics dont work. If you dont know how to post 'em I can show ya.

clxfiles · Post by **clxfiles** » Tue Feb 21, 2006 11:06 pm

Yeah I'd appreciate that. I'm trying to figure the images out.

clxfiles · Post by **clxfiles** » Tue Feb 21, 2006 11:32 pm

Thanks SHAUN... I kept using the address in the URL rather than the property. I appreciate your help.

SHAUN · Post by **SHAUN** » Tue Feb 21, 2006 11:49 pm

No prob, always fun helpin out people.

frizzen · Post by **frizzen** » Wed Feb 22, 2006 2:38 am

photobucket makes it even easier, they already have one of the 3 urls you can highlite for it that has the {img} tags. Just copy and paste that shit

crazydave · Post by **crazydave** » Wed Feb 22, 2006 6:55 am

Alright, I think I see your mistake, on the flipped FETs, the pin with the jumper, is it making contact with the pad? Its not supposed to. Actually now that I look again, you're also using the wrong pins.

Here, this is for bits, but it'll show you the correct way to flip the FETs.

clxfiles · Post by **clxfiles** » Wed Feb 22, 2006 10:03 am

Thanks CD... I can't wait to try that tonight. Now I'm gonna be clock watchin at work all day.
I think uA must have flipped those topside fets to be sitting on their top, and connected the pin to that wire only. I thought it was connected to the pad and was sitting regularly. Hard to tell with all that black paint or whatever on it.
I was looking for that chart you posted all night, the thread that is linked from the article on FETs no longer has the pics on them. That's why I figured I'd just try to copy.

Thanks PIMP!!!!

I checked out digikey's site to buy some more fets and the ones I got last time were out of stock. Will any of the 2502's do?? The performance all seem to be the same.

Digi-Key Part Number Manufacturer Part Number Description Vendor Transistor Type Voltage-Rated Current Rating Package / Case Packaging Quantity Available Unit Price
Min Qty

IRLML2502PBFTR-ND IRLML2502TRPBF MOSFET N-CH 20V 4.2A SOT-23 International Rectifier N-Channel 20V 4.2A SOT-23 Tape & Reel (TR) 84000 0.22500
3000
IRLML2502PBFCT-ND IRLML2502TRPBF MOSFET N-CH 20V 4.2A SOT-23 International Rectifier N-Channel 20V 4.2A SOT-23 Cut Tape (CT) 4393 0.77000
1
IRLML2502TR-ND IRLML2502TR MOSFET N-CH 20V 4.2A SOT-23 International Rectifier N-Channel 20V 4.2A Micro3TM(SOT-23) Tape & Reel (TR) Non-Stock 0.21000
3000
IRLML2502CT-ND IRLML2502TR MOSFET N-CH 20V 4.2A SOT-23 International Rectifier N-Channel 20V 4.2A Micro3TM(SOT-23) Cut Tape (CT) Non-Stock 0.45000
1

SuperFly · Post by **SuperFly** » Wed Feb 22, 2006 10:59 am

before you order those up, I'd ask CD about the P-channel vs. N-channel fets. I know nothing about them, but I think I remember you can avoid the flipping and jumpering by using P-channels in a couple spots. I may be talking out my ass, but I'm sure someone will let me know.

clxfiles · Post by **clxfiles** » Wed Feb 22, 2006 1:34 pm

CrazyDave?? Or anyone, if you know for sure, can you "skewl" us in the proper usage?
I thought the P-Channel fets were the 6401's and were only used in the SE board. I do have a coupe of them, so if they don't need to be flipped I'll try that on my next pcb experiment.

crazydave · Post by **crazydave** » Wed Feb 22, 2006 4:44 pm

Yep, the 6401s are a direct swap for the p-channels.

Going by the numbers the P-channels have twice the resistance as the N-channels, hence the use of all N-channels and the flipping, but that's at a 5v rating, at the voltage we're using I don't see any difference in performance. I prefer to just use the P-channel FETs as opposed to flipping N-channels, because I can do a FET mod in 10 minutes by just doing a direct swap, and I don't have to worry about any wires coming loose.

clxfiles · Post by **clxfiles** » Thu Feb 23, 2006 1:38 am

Flipped those N-channels on 2 boards and they both worked awesome. Had a little trouble with reverse on one of them but eventually found the loose connection. Now it runs like a champ.

Also, I finally got a wheel mod to work. Swiped them off an Import Racer. There's a little wobble in front but it shouldn't be too hard to adjust. Question now is what do I do with the Import Racer body.

Thanks for all the help pimps!!!

clxfiles · Post by **clxfiles** » Fri Feb 24, 2006 5:51 pm

OK, got stuck on another one last night. I used the P Channel, 6401s, in place of the fets that are turned in your diagram, and the n channels on the ones they were jumperred to. I didn't swap the last 2 at all. I don't get any power to the motor or steering. Was I supposed to jump anything? I didn't, I just swapped the old trannys out and the fets in, lead for lead.

This is on a bit clone pcb that was the same layout as the diagram.