Controller Port Problem/Unwanted Autofire

[TailChao]

Cross answering with this, just in case anyone else runs into a similar issue.

 

The four paddle inputs (I0 - I3) have indeterminate states without a ProLine (or compatible) joystick attached. Usually they'll stay low, but on certain units they'll drift high after the TIA warms up - or just immediately. This can be interpreted as spurious presses by game software using the two-button input mode, and seems to get worse with age.

 

Xevious starts up in two-button mode, regardless of the left difficulty switch's state. It'll only switch into one-button mode when it detects a VCS style press. So if you're using a ProLine controller and your paddle inputs are hosed - it'll just keep firing.

 

Galaga operates exclusively in one-button mode, so if it's working that at least indicates I4 and I5 could be fine. But it doesn't say anything about I0 - I3.

 

Thing to try...

• Try using a single button controller with Xevious and see if it works.
• Check R36, R37, R38, and R39 to make sure they're in spec.
• Replace the TIA.
• Replace the 7805.

[thenickman100]

9 minutes ago, TailChao said:

Galaga operates exclusively in one-button mode, so if it's working that at least indicates I4 and I5 could be fine. But it doesn't say anything about I0 - I3.

Galaga only worked fine after I removed the TIA and put it back in.  Before I tried that, every game--including Galaga--was experiencing the same issue.  Xevious is the game that caused the 7800 to act up in the first place, though.

[TailChao]

22 minutes ago, thenickman100 said:

Galaga only worked fine after I removed the TIA and put it back in.  Before I tried that, every game--including Galaga--was experiencing the same issue.  Xevious is the game that caused the 7800 to act up in the first place, though.

This definitely sounds like a bad TIA or a really lousy continuity issue. Do you have another TIA to swap in and try?

[+Mitch]

If reinsertIng the TIA fixed it, then it could be a bad socket as well.

 

Mitch

[thenickman100]

On 9/25/2019 at 4:40 PM, TailChao said:

This definitely sounds like a bad TIA or a really lousy continuity issue. Do you have another TIA to swap in and try?

Unfortunately, I do not.  I might pick up a 2600 at some point to try the TIA, but I doubt it will be anytime soon.  If one game is causing it, is there any way it is overloading the board/TIA?

As to your other suggestions, I already reassembled the system and returned the game.  I'll probably stay away from 7800 repros from now on, aside from homebrews.

[TailChao]

12 hours ago, thenickman100 said:

Unfortunately, I do not.  I might pick up a 2600 at some point to try the TIA, but I doubt it will be anytime soon.  If one game is causing it, is there any way it is overloading the board/TIA?

It's possible, but usually if a cartridge is causing a supply rail to sag you'll see other symptoms like video issues or instability.

 

The whole input block on the 7800 is extremely fragile - so the TIA, RIOT, and ProLine support circuitry could have been damaged years ago and it's just now that the components are starting to fail.