Joystick conversion question

[Delcion]

I'm a lowbie electroinics tinkerer and modder <greetings!>.  I'm currently trying to figure out how to replace the 500k standard pots in a vintage game console joystick with these 250k mini pots from a modern controller.  I know I can't do a drop in because the voltage sweep probably won't be great enough.  I've through about trying to drive a digital pot with the analog input from the mini pots or try to drive a transistor to get the sweep I need.  I haven't sat down and measured the voltage range it actually uses, but I know it's a 5V input.  Any ideas or suggestions?

[Maxlor]

Why do you have to use 250k pots? Are no other ones available?

Have you analyzed the circuit in which the pots are used? If they're supplied with VDD and GND directly, the pots value won't matter much and a 250k will work just as well as a 500k. If there are other resistors nearby, it might be easiest to change those too to accomodate the 250k pot.

More details would make it easier to give a better answer

[Rerouter]

I agree with maxlor, for a joystick, short of resistors on top and bottom to limit the range i can't see why they would be connected to anything more than VCC and ground..

[Delcion]

If this helps any, I have the schematics for the I/O on the system.  It's an Atari 5200.

https://atariage.com/5200/archives/schematics/Schematic_5200_IO_High.html

the reason I'm wanting to use 250k mini pots like in Playstation joysticks is I haven't found 500k versions of the mini pots.

[Rerouter]

pin 9 is your supply, 10 is horizontal, and 11 is vertical, it works through a time constant to work out the position,

but now looking at it... boy did they go the extra mile to not use a separate ADC, a constant current driver feeds pin 9, and the 1nF and 47nF caps you see on pins 10 and 11 make up the RC time constant,

try your 250K pot, but double those capacitor values, that should square things up.

[Delcion]

awesome stuff.  Thanks a lot!