Jittery CX-80 Trak-Ball

[+Karl G]

I bought a CX-80 Trak-Ball that was advertised to be in good condition off of Ebay. When I tried it, it was jittery. I've only tried joystick mode so far, but I can't imagine that analog mode would be any better.

 

Presumably I'm entitled to a refund, but I don't like the idea that the seller might just end up pitching the thing. I understand that some devices can be restored just via a good cleaning.

 

I'm wanting to get an idea from those with more experience how likely it would be that restoration would be simple, and how to go about it. For starters, I don't even see any screw holes on the thing. Any advice for a hardware newbie would be appreciated.

[alex_79]

Here there are pictures of a disassembled cx80:
http://www.the-liberator.net/site-files/retro-games/hardware/Atari-2600/atari-2600-trak-ball-controller.htm
Apparently, the screws are under the rubber feet.
Try cleaning the rollers and the ball and maybe put a few drops of oil into the bearings, if they don't spin freely.

If you have an Harmony cart, try the hacks in the first post of this thread to test the real trakball mode. (You most likely will need the roms labeled "CX22" or "atari trakball")

[BigO]

The joystick mode may bring IC's into play that are not used in real trackball mode (technically not analog). It would be worth a few minutes to try TB mode if you have a game that supports it. Several downloadable ROMs (as alex_79 mentioned) will work with that mode if you have a multi-cart such as a Harmony.

 

That said, can you elaborate on "jittery"?

 

What really happens in joystick mode is that the circuitry reacts to how quickly the optical encoder is being actuated and turns on the output that a digital joystick would turn on. There is a certain speed at which the joystick output would be oscillating on and off. If you were playing a game which reads the joystick port at a high rate, the game might be able to react to that threshold speed quickly enough that you'd see the jerky motion. That's a bit of stretch, really, but would certainly be worth testing on several different games.

 

There could be dust/lint/hair/rhinoceri/etc. in the slot where the optical encoder wheel runs. That'd be the easiest problem to fix.

[+Karl G]

I'll have to play with it a bit more to get a better description, but the motion feels inconsistent, and also sometimes jumps slightly in the opposite direction. I think I will at least try my hand at cleaning it instead of returning it. It does seem like a nifty bit of hardware. I do have a Harmony cart, and can test analog mode, too.

[BigO]

Just looking at the schematic for the CX80... As it appears to me, the primary electronic failure that could cause jitter would be the 4098 chip. It's job would be to stretch the pulses from the optical encoders to assure a minimum output length. If these are failing, the output of the joystick emulator could just be a series of very short pulses rather than the normal longer pulses which become a steady state signal above a certain spin rate. So, short output pulses = jittery movement.

[Swami]

I'll have to play with it a bit more to get a better description, but the motion feels inconsistent, and also sometimes jumps slightly in the opposite direction. I think I will at least try my hand at cleaning it instead of returning it. It does seem like a nifty bit of hardware. I do have a Harmony cart, and can test analog mode, too.

 

I would start simple, as it could be something basic and a lot of mundane things can make a trackball "jitter".

 

What hardware are you playing it on and what games have you tried in joystick mode? I would also test to make sure you don't have one with ST mouse internals, which might give goofy behavior even in joystick mode. There is a test rom for this along with trackball hacks on this page:

 

http://atariage.com/forums/topic/243453-atari-2600-trak-ball-games/

 

You can also study this thread if you have a 2600daptor ][ and want to try it on Stella, but I've found the CX22 internal CX80 a little awkward still in Stella, as you will read at the end of the thread:

http://atariage.com/forums/topic/269337-colony-7-2600-in-stella-with-trackball/