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@allObjects
...here my version(s - had two of those to do indoor - on table - races while living in a crammed place in a very cold region...).
On the back of the board you see F(orward)-B(ackward) with motor connections (red and black wires), R(ight) and L(eft) with connection to one side of the solenoids (white wires - disconnected) and VCC (brown wires).
The solenoids are driven with NPN 'open-collector' - assuming it is just - transistors: VCC-Load[=solenoid]-Collector/Emitter-GND... and if NMOS FETs switching the low side, there fore, more precisely: VCC-Load[=solenoid]-Drain/Source-GND (Q3 and Q2) - driven over ~1K Ohms (102 --- 10 x 10^2).
Q4 and Q5 - same as for solenoids control (EY1) - together with Q6 and Q7 - some PNP transistor (or PMOS FETs; IYA - IY^ ?)- build the H-Bridge for the motor control - hight side driven over ~100 Ohms (101 --- 10 x 10^1) from opposite driver, and low side driven over ...cannot see it.
The solenoids have a resistance of about 20 Ohms each. Between them is the cylindric neodine magnet moving the steering rod to the left and right, and over it is the pivot of the spring with two legs centering it to and via the trim post (white plastic with the flat side). A very simple but very smart way to have it all: control and trim (for going straight when no solenoid active).
There is nothing additional to the steering but the alternate powering of the solenoids. Try to measure the resistance of yours... If it broke of, the wire is lacquered and therefore you did not get a pass through.
Power is a single 1.2V 80mA NiCd(?) cell. What you cannot easily see on the backside - under the 100uF 6.3V electrolytic capacitor - there is a (3+1) four-legged SMD IC(?) which I assume makes a voltage booster with the L3 and glass diode D1 on the front side. IC reads DF N6 - guess just the package ID :(... and just another transistor with cheap booster switch for HF and control side only...
The boards are from about 2004. The switch is my addition... to have the car ready charged for a quick race. The constant on drained the battery pretty quickly, even when car not driven.
References: datasheet datasheets2 datasheet3.
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