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Anyone have ANY info on a mosfet mod for Precious clones? I know I can pay MicroAmps to do it, but I want to do this myself. I'm having a hell of a time finding out info about the Precious PCB/schematic. Any info, pics, whatever would be appreciated. Thanks!

search the Weird Science forum holmes
I'm pretty sure the mosfet will work for precious - ph2t and crazydave are the pimps here to ask though to be sure.

I've searched all the micro R/C forums I could find to no avail. The only clearly stated mosfet mods I could find were for for LXX clones. I haven't seen any useful info for Precious, Shens, or Panthers. Here's a pic of the top of the PCB:



The main connections to the board are at the top of the pic. From left to right they are Vcc, F(orward), B(ackward), L, R, Gnd. I've never seen a PCB like this in the forums. Hopefully someone can help me out

-Laterz

Dude, first off, welcome to the forums.

The fact that you posted a pic of the pcb AND stated the order of the connections makes it a lot easier to help!

From what you have said I have the following:

The two transistors in the top left of the PCB connect straight to the motor terminals. These two are definately one half of the h-bridge (the name of a common circuit design use in motor control).

The two transistors in the top right are most likely the steering transistors.

Now, the steering transistors are usually NPN type. BUT the h-bridge will have two NPN and two PNP type transistors. What comes next is like a process of elimination.

The NPN transistors (all of them) will have a product code or marking on them of some kind. This SHOULD be the same marking for the steering and one half of the h-bridge.

There will be two transistors that have different markings, these will be the two PNP transistors......

get my drift?

What makes this pic a little harder to figure out is that you have 1 more transistor than a usual BCG circuit board. What I mean by this is the following:

2 * NPN + 2 PNP for motor h-bridge
2 * NPN for steering
1 * NPN for the RF receiver.

This is standard, but in the pic there are 8 transistors!!!!

First of all, locate the transistors that have the matching markings on them.

My bet is this:

- The two transistors on the top left are NPN (1/2 of hbridge)
- The two transistors on the top right are NPN (steering)
- The two transistors BELOW the top left ones (but left of the black blob) are possibly PNP (the case markings should differ for these two in particular)( the other 1/2 of the hbridge)

See how you go with this and once that's figured we can take the next step. Also if you could post some really hi-res photos (just link them) that would help!

Best of luck!

ph2t.

ph2t also sells a badass "biff" board that would make your life easier on th e install.

Here's a link to a bigger pic of the board:
http://204.130.156.18/~cvinluan/pcbhigh.jpg
EDIT: betty k. is correct. I fixed my picture. Gees, but now the placement of the transistors is confusing me more. If only I knew more about electronic circuits

I labeled the different transistors I found on the board. I think the compononent in the lower right is a transitor and it appears to be labeled LY. I'm assuming that the 6c transistors are NPN. Now I have to figure out which transistors belong to the h-bridge. What's sorta weird is that it appears that PNP transistors are at the outputs rather than the expected NPN types.

ph2t, I really appreciate your help. Do you know how to connect your biff board to this PCB? If so I might just have to scrape up the money to buy one and chalk it up as a "learning" expense

hogjowlz, I would love to buy a biff board, but I just spent my extra cash on a portasol solering iron And I tend to do things the hard way

i think you may have mislabelled one of those transistors. i've got a pic here where i've colour coded the matching transistors
http://community.webshots.com/photo/133 ... 2224SGvxwZ
my one is 35mhz so that could be the reason for the difference.

Damnit!!! Finally mapped all the transistors on the board!!! Now people can mod this mofo Betty k., hope you don't mind me modifying your pic of the precious pcb...



Red are NPN & PNP are yellow. Blue are the resistors where the "on" signal activates the base of the first transistor in the h-bridge. Purple are the resistors that trigger the base of the second transistor in the h-bridge. If someone could verify these things for me, it would be even better. My electronics skills/knowledge isn't too great and I often screw things up

I'm planning on trying to mod this board soon. I don't have any irlml2502 fets, only the odd shaped chipFET package of the NTHS5404 from ON Semiconductor. So its gonna have to be external turbo style, unless someone wants to send me some irlml2502 fets