View Full Version : Car not moving forward or reverse

2005.12.11, 10:59 PM
Hello, I am new to the forum, looks like I will spend a lot of time here since I just bought a mini Z formula 1 a couple days ago from a guy who used to race it. I have a problem with my mini-z, maybe some of the FET expert out there can help out.

I browsed through the threads and did some searches through the forums, so I have some ideas of the problem, but I want to get some feedback before I start messing with the car.

When I bought it, the seller told me that the FET needs to be re-soldered because it's loose. He said it happened because the FET was a little too high and when the car flipped over, the impact from the body caused the FET connection to be broken.

I put in the batteries the next day and tried it and... it works. So, I played it a couple of times around the the house, I only went full throttle half the time because there is not much space. I smelled (not exactly burning smell) something from the motor, so I thought I didn't want to overheat it and gave the car a rest.

In the afternoon the car won't move when I was going to play it again. It works when I pulled the body out. So I put in the body but didn't put it tight enough so the body won't touch the electronics. After a few minutes, the car stop moving again, until now.

The car moves again whenever I pressed the FET, it does get really hot however.

My question is:

does this sound like a loose FET problem and would a re-solder fix the problem? see picture below. the FET that I was pushed to get the car moving again was the FET at the end of the PCB.

To avoid this problem in the future, I plan to cut a hole in the body so the FET won't get pushed again. What's the best way to cut the body? A cutter won't do it because the body is too hard.

is it normal for the FET to get hot? or did it get overheated because the connection to the board was loose?

last question: does anyone know any installer in the bay area other than club28rc and hobbytown USA?



2005.12.12, 09:42 AM
First, welcome to the forums and congrats on the F1 purchase.

Here's a little information that may help you decide.

What you actually have on that car is a FET stack. In this case it's a 2x3 (or 3x2) because you have 3 Transistors stacked on top of each other.

It does sound like your problem could be a FET problem. A FET upgrade (just replacing the stock FETS with a single layer of better FETS) or FET stack (what you have) allows you to run faster motors without burning out the stock FETS.

A "faster" motor draws more current and if you draw too much you can fry your stock FETS.

In my opinion, I think the F1 is pretty fast with the stock FETS. You can safely run an X-speed motor (which it looks like you have) without any problems.

Before you decide to hack the body, I have another suggestion. I would get someone to remove the FET stack and just replace the stack with a single layer of upgraded FETS. You could probably just use two of the FETS from the 2x3 stack that you have.

This should make it easier to get a nice, clean, reliable install. I am sure an upgraded F1 will be faster than you ever need it to be. You will still be able to run a lot of motors if you ever decide that you don't like the X-speed and the acceleration will be better than a stock F1.

Maybe if there is a member in your area that is handy with a soldering iron, they could help you out. I would be able to do it, but I am on the other side of the country. The shop could do a 2x2 stack for you for $35.


Best of luck, whatever you decide.

2005.12.12, 10:43 AM
Yep... loose fet, but I wouldn't suggest just re-soldering it. I too would either go to a single layer turbo fet, or even go as far as just going back to stock. It is possible to just remove those top fets, but it's delicate work. and, there is no guarantee that the fets underneath were not afffected by the shorting. You have options, but for a newbie to be working on fets right away... you're certainly taking on alot. (not unheard of though) Key things... none of the forward "feet" should have any cross connections, it doesn't matter for the feet towards the rear. Here's bye bye's excellent fet vid post...


Good luck !

2005.12.12, 10:43 AM
Spoon is on the money with tips. It looks as though it needs to be resoldered at the board. I would suggest either a 1x1 or 2x2. A 2x2 is more than adequate for now and probably for as long as you will use it. I would suggest you take it to club28 and have them take a look. I've been to club28rc and they did my first 2x2. They do very good work. Just ask them if they can either touch it up or remove the top fets. Shouldn't cost much for removal and they are in your area. If I still lived in California I would do it for you ;)


2005.12.12, 10:54 PM
thank you all for the responses. I may re-solder the FETs or go to club28 RC and have them take a look at it. i have some soldering experience from back in jr high, so i think i can do it.

i'll keep you all posted. i love this car, i have never seen a body style built as precise as these mini-zs in my RC experience with 1/10 or 1/18 scale cars.

on a separate note, i wonder if these FET upgrade can be applied to cheap RC cars made by Nikko, etc. has anyone tried?

do they have similar circuit boards? i know these cars don't have proportional speed control, but if we can make these nikko RC Cars go 20 mph++, that would be cool!

2005.12.13, 05:11 AM
thanks to your pics... looks like the stack nearest to the edge of the board (in the first picture) is misaligned... the second leg from the bottom seems suspect... i would recommend resoldering the whole stack... if you're not too sure or confident about your soldering skills, i suggest having it done professionally...

good luck...

2005.12.13, 11:13 AM
i have some soldering experience from back in jr high, so i think i can do it.

Heh- I took 2 quarters of electronics in college, and I botched my first (and last) FET attempt.

It's worth a try though....just be careful not to lift your tabs or fry the PCB- it's a really really tiny scale for soldering.

2005.12.13, 12:10 PM
If the Fets are ok, try leaning the stack towards the center of the board this way you get to keep your fet stack and run a clean body. I've got mine done this way and still am able to use the antenna bridge. I post apicture but for the life of me I can't remember were i put them??

2005.12.16, 12:40 AM
ok, so I bought a solder from radio shack, similar to what byebye has in his video, except mine has a slightly smaller tip.

then I tried to reconnect the legs with the base, but failed. What happened was that the 2 of the 4 legs touched each other when I was trying to connect each one to the base. So, I tried to separate them.

after trying several times, I gave up and decided that it would be easier to do the work if the whole stack is aligned properly.

While trying to aligned the stack, I accidentally removed the 2 chips on top of the stacks. The bottom stack didn't get removed.

so i decided to fix the bottom stack and made sure that the legs are soldered properly and not touching each other.

by accident, the top chip from the other stack also got removed.

and guess what, the car works now! i don't know how i did it, must be pure luck after all that failed attempts. :-)

it does not go as fast as it was last week though with the 3 stacks.

is it safe to run the car with only ane FET?