amplifiertransistors
The green points are from the video controller output, and yellow point is to the CRT base driver.
ideally small signals are fed to the base of the transistor but here it goes to the collector via diodes. wondering how these transistors will do the job of amplification of the signals.
I might be totally wrong here but my excuse is the question is very confusing. The circuit shown above is trying to pull the 2.52 V line down to ground through the 10R resistor and an NPN transistor. The original (pre-hacked circuit) you describe was it this? Forward and Reverse are mutually exclusive as are left and right. On the vehicles I've hacked into they usually have a spring loaded centre off action (joystick). Are you absolutely certain the pole of the switch went to ground (0v)?
You say when you touched R2 (140k) the remote worked sending a signal to the car. This sounds like you were acting as an input signal. By touching the input your body as an aerial picking up the local EM field, the 140K resistor being large enough to prevent the weak signal from being shorted out. That suggests to me that the control input needs to go HIGH rather than LOW and that the switch was actually connected to the positive rail. To test this hypothesis connect up the circuit below and let us know what happened.
Bipolar junction transistors (BJT) have 3 primary modes of operation:
In cases 2 and 3 there is current flowing from the collector to the emitter.
You can saturate the BJT by attaching a smaller load (i.e. higher resistance) than the linear limit allows. Think of a pipe with a valve. If there's something clogging the pipe upstream, at a certain point no matter how much you open the valve you're not going to get any more fluid flowing through the valve.
Yes, the electrons do literally move to generate the current, though this isn't directly used for most electrical engineering analysis.
For most EE analysis we don't consider the motions of charged particles directly, instead relying completely on the abstract concept of current. This is an approximation of reality, but it turns out to be remarkably good in most cases.
Ironically, in my day-to-day work with plasma physics we do consider the motion of charged particles instead of relying on abstract currents because the analysis does differ depending on what species are moving and where/how fast they are moving.
Best Answer
Obviously, the transistors are not there to amplify the video signal. Instead, they seem to be functioning as a clamp that keeps the video signals grounded (through two diodes) whenever the red line at the top has less than about 7.7 V on it.
When the voltage is high enough to turn Q202 on, Q203 is turned off and the diode cathodes are pulled up, effectively switching them off and allowing the video signals to operate over their full range.