Here is the basic analysis I use when determining what transistor is what in the h-bridge so I know which ones are pin-for-pin replacements (the NPN trannies) and the ones that need to be custom connected (the PNP transistors). I've used this method on several boards including a LXX pcb and a clone pcb that both had different layouts to the stock TOMY/MS pcb's. There's no reason that you can't use this method on a ZZ pcb as well.
First get a multimeter and set it to a low voltage scale, on my DMM I use the 2.0V setting. Connect the MM (multimeter) -VE probe to the ground plane on the pcb. I usually use an aligator clip to clip the -VE probe onto the pcb where the -VE battery wire is soldered on. This keeps it in place and allows me to move around with the +VE probe to find the information I need.
Next look where the motor wires terminate on the pcb and focus your attention there. You should see the black packaged transistors close to this area. They might all be close, some will be spread out, each manufacturer's pcb is different. This little black package is known as SOT-23, where 3 is the amount of pins and 2 means how many on one side. So from this we know that the transistor packages have two pins on one side and one on the other side.
This diagram below show the pinouts for a SOT-23 based package. This is for a MOSFET and not a normal TRANSISTOR but the pinouts are the same when you relate the two types of transistors to each other. This is for a NPN transistor vs. a n-channel MOSFET.
This only accounts for 2 of the 4 transistors that will be removed.
MOSFET BJT
Gate = Base
Drain = Collector
Source = Emitter
So why I say all this? I know it sounds confusing but what I'm trying to establish is
where you need to put the Multimeter to be able to tell what transistors are needed to be removed.
So what you need to do is start probing each of the transistors to find which ones are the NPN ones and then which ones are the PNP ones.
With the +VE probe (red one!) from your multimeter use it to test the voltage on
PIN 1 of the transistor in test. Use the diagram above to know which pin this is.
So hold the MM on this pin and then push the
FWD or
REV buttons on the controller. If this transistor is connected you will see the voltage go from 0 to
0.7V when you push the FWD or REV button. If the voltage is anything different before and after you press the button then ignore this transistor and move on to the next one. You need to find this
0.7V to know what to do next.
Do this method until you find the
2 transistors that go to
0.7V for FWD and REV on the controller respectively.
These are the two transistors that will have the mosfets soldered directly in place pin-for-pin without any problems.
Now you need to find the two transistors that are PNP. These two are the ones where the MOSFETS
can not be soldered in pin for pin and need the mosfets to be connected a little bit differently.
To find these transistors I use a process of elimination because it's sometimes tricky to determine these transistors but using the process described above.
I basically find the two steering transistors by using the method above
EXCEPT instead of pushing FWD/REV on the controller I push LEFT/RIGHT. Once you have found these two transistors it's pretty much a process of elimination.
You have found the two NPN transistors are described above, you have also foudn the two steering transistors as well.
So the only two transistors left are the PNP ones that should be connected using the diagrams jeep posted earlier in this thread.
You might say that this wouldn't work because there is actually three transistors left over, not two. We'll you're right, but one of these transistors is for the RF receiver stage and will be
a fair distance away from the other two (PNP) transistors.
That's it! You have now found the 2 NPN transistors (these are pin-for-pin replacements for the MOSFETs) and the 2 PNP transistors (these are the ones connnected differently as shown earlier in this thread.).
And now this longwinded post is coming to an end..............
ph2t.
