Atari 2600 Jittering problem while using paddles ...

[Merowech]

Hello

 

Hopefully someone more experienced can help me with my Atari 2600 problem:

 

I fell in love with the Atari VCS last year when I got a Flashback 8 Gold HD. Finally I bought a real Atari VCS (Darth Vader, NTSC version) on eBay a couple of weeks ago. It was allready modded to A/V output by the previous owner.

 

Unfortunately it shows some heavy jittering/shaking when using paddle games. First I carefully cleaned the Paddle pots but this didn't help (and it happens with other controllers as well). During cleaning I accidentally found out that jittering will stop as long as I touch the bare cable which is soldered to the circular resistor with my hands. Because there was a loose connection within the power supply I bought a new power adaptor but this did not affect this jittering problem.

 

I am not a technician but I guess if something simple like touching an electrical contact can stop this jittering it might be fixable. I added a Youtube video which shows the problem and some pictures of the paddle and mainboard. On the paddle picture I point with a screwdriver to the sensitive/touchy contact. The red circle on the mainboard picture shows the corresponding electric solder bump on the board - touching this point with my hand will stop jittering as well.

 

Because it is not that easy to get an NTSC Atari in Germany (without ordering from the USA) it would be great if I could repair this unit.

 

I will be very grateful if someone could help me with some educated guesses or hints how to solve this problem

 

Youtube link:

 

[Rom Collector]

Hallo.

 

I'm not an Atari expert, and was hoping someone else would step in and help. 

Anyway, I would think something isn't grounded properly. Try using a decoupling capacitor between the connection you show and ground.

Try .1 - .001 uf capacitor.

Viel Glück!

[+BigO]

Try touching that contact with something nonconductive like a wooden skewer. If you can reproduce the results using that, then there is probably a mechanical problem with how that terminal connects to the resistive material in the potentiometer.

 

If you know how to solder, you could also try replacing that pot with the one from the other controller to confirm that the problem is directly with the potentiometer. I suppose you could even just move that wire over to the unused terminal on that pot. It would make the paddle work backward, but it would help identify the problem.

[classicgamer74]

Jittery paddles is something that a majority of us have had to deal with.  These experts on here will point you in the right direction. 

[Rik]

I had this problem with all my paddles and taking apart the pots and cleaning them solved the problem luckily. I am going to keep looking back at this thread as i'm sure the many experts here can help solve the issue which would also be great for future know how, good luck!

Edited August 4, 2019 by Rik

[willis]

The video shows you playing Kaboom, just a heads up as that game is known for being slightly jittery
 

 

[+BigO]

I failed to see the part that says touching the solder point on the board also stops the jittering. In that case, I don't know what the problem is. Since that circuit is already feeding a .1 uf capacitor, I would expect that adding a few picofarad by touching it would have much effect.

 

If it really is only a problem with Kaboom as observed by willis, then there's not really any reason to do anything. If so, also does make me curious exactly what the cause of the jitter is in Kaboom. I always assumed that it was programmed to be overly sensitive to a minute change in resistance, or something like that. I haven't really studied the problem, but guess that it jitters at resistance values very near the threshold of a change to the next screen position.

 

Now I'll have to poke around and see if anyone has determined the actual root cause of the Kaboom jitters. I hadn't thought to check that behavior with the digital paddle experiments I've been tinkering with. I might try to use a high precision potentiometer which is not so subject to slight movements as the standard paddle. Does the jitter only happen after a movement, or will it continue to jitter with a completely stable input. Does it jitter when bombs are not dropping? (just some notes for my future self)

[Atarian7]

I've played a little Kaboom! myself and can vouch for the game being a tiny bit jittery.  But it only jitters a little when standing still.  I haven't noticed any

jitteriness when moving the paddles.