Tek 2230, Alternatives to the cursor control pot.


Pitpat
 

Hi guys, I've recently (with the kind help of Albert O.) repaired this beauty.
The last thing is left to do is replacing the now broken cursor control potentiometer.
From what I've seen on the schematics should be an 10k dual continuos push-push pot.
I've found some replacementents on ebay but they all comes as pre-used and with an absurd pricing so it isn't really an option... I've found this guy
http://www.jetecnet.com/2230_Encoder/2230encoder.html
Who did a fantastic job converting an optical encoder to an analog signal but unfortunatly it looks like a dead project with no public schematics, i would like to attempt someting similar but maybe using a more convenient digital potentiometer like the MCP41010-E/P paired with an encoder.
The point is that I couldn't find any direction on how the original potentiometer works, from my understanding the dual 10k ohm variable works in opposition so that there's no "dead zones" caused by the 360 degrees of rotation but thats all...
Let me know what you think.
PS. I'll post a photo of the schematics
Thanks!
Federico


Albert Otten
 

On Sun, Jul 4, 2021 at 05:34 PM, Pitpat wrote:


The point is that I couldn't find any direction on how the original
potentiometer works, from my understanding the dual 10k ohm variable works in
opposition so that there's no "dead zones" caused by the 360 degrees of
rotation but thats all...
Hi Federico,

Any progress so far?
It's true that the pots work in opposite directions. In my 2232 this is achieved by interchanging assignment of 0V and +5V to the terminals. With an ordinary dual pot this would not prevent dead zones to occur simultaneously for both wipers. The trick here is that one wiper is rotated w.r.t. the other. Not over 180 degrees what I expected, but enough to avoid simultaneous dead zones.
When there are no simultaneous dead zones the processor can always determine the direction of knob rotation. I don't see the purpose of opposite directions.

Albert