Camerica's Lockout Circuit
Lockout portion of PCB
Circuit Diagram
How it works:
Operation is quite simple. The one line from the mapper (see the Camerica page for
details on where it hooks up and such) is simply toggled multiple times at several kilohertz
on startup. This apparently fools the lockout chip into attempting to communicate.
The rest of the circuit simply generates a negative voltage of around -3.6V or thereabouts.
This then crashes the chip, which is stuck in a non-resetting state, letting the game run.
Circuit Operation:
The voltage inverter is quite elegant, and works using a cutoff oscillator. The NPN transistor
is biased on by the 39K resistor, which then turns the PNP transistor on. When this happens,
the NPN transistor is then turned off again through the 1K resistor and 330pf capacitor.
Once the cap charges, the transistor turns back on, and the cycle repeats. These pulses
of current across the inductor cause it to build up a magnetic field when the transistors are
on, and when the transistors turn off, the field collapses, dumping the reverse EMF voltage
through the diode and into the 47uf capacitor. This voltage is then run through a 1.5 ohm
or 12 ohm resistor (varies by cart), through the switch, and finally to the cart connector.
The zener diode cuts off base drive to the NPN transistor when the voltage across it exceeds
3V+ the drop of the transistor junction, which is around .6V. Thus, the final output
voltage of the circuit is around -3.6 to -3.4V. The remaining diode to ground on the base
of the NPN transistor prevents negative spikes from damaging it.
The infamous switch on the back of the cart simply connects the negative supply to the cart
edge. Toploaders will NOT be happy if it is turned on! This will cause the circuit to draw
tons of current, which will most likely fry it if the console is left on too long. On my
console, it causes the screen to go black with grey wavy lines, and the audio produces a loud
buzz.
|
