DB9 Borked?

[Rick Dangerous]

I got in my first 7800 off ebay recently and finally had time to test it today.

 

I tried multiple controllers, but every one the character goes to the right.  Some won't even let me move at all (Froggie.)  Other games even got stuck on the menu screen when i tested them (Dig Dug.)

 

Anyone encountered this?  Is it a loose wire inside most likely; or something more complex like a bad chip that won't be easy to repair/replace?  Was going to have this console re-capped and S-video modded, but if there are some deeper problems that aren't easily fixable i'll honestly probably return it.   

 

Thanks! 

 

 

[+-^CrossBow^-]

Well if multiple controllers are causing this then it could very well be an issue with the TIA or the RIOT chips in the console. But it would be best to know if the console is acting like a direction is always pressed or a fire button.

 

[+DrVenkman]

RIOT controls directionals, TIA reads triggers and paddle lines. My inclination is bad RIOT. Unfortunately, I've run into several bad RIOTs fixing 2600's in the last couple years so they are clearly subject to damage, probably static discharge related.

[Zonie]

In a 2600 hex buffer IC can do this. Cheapest place to start. Static kills that one. Not sure if the 7800 has one.

 

 

Edited January 25, 2021 by Zonie

[+DrVenkman]

14 minutes ago, Zonie said:

In a 2600 hex buffer IC can do this. Cheapest place to start. Static kills that one. Not sure if the 7800 has one.

 

 

Only 6-switch units have 4050 hex buffers; 4-switch machines (Woodies and Vaders) do not. There's a Technical Service Bulletin for Atari about installing a Zener diode to help protect against static but none of the 4-switch machines I own (4 currently) had it done. The 7800 does not have a 4050 in the design either, though it does have Zener diodes on each of the directionals along with filter capacitors. It's possible one of those has failed.

 

In any case, the OP will have to open it up to do any real further diagnostics. Sadly, most 7800's are not socketed so final diagnosis and repair will likely take some tools and skill. 

[Rick Dangerous]

It's stuck like I'm pressing to the right constantly.

 

So it is repairable theoretically with some parts/soldering?

 

I just want to make sure it's not some unobtainable chip I would need. 

[+DrVenkman]

2 minutes ago, Rick Dangerous said:

It's stuck like I'm pressing to the right constantly.

 

So it is repairable theoretically with some parts/soldering?

 

I just want to make sure it's not some unobtainable chip I would need. 

No chip is unavailable, and yes, anything is repairable with the right tools and skill.  

[Zonie]

6 minutes ago, DrVenkman said:

Only 6-switch units have 4050 hex buffers; 4-switch machines (Woodies and Vaders) do not. There's a Technical Service Bulletin for Atari about installing a Zener diode to help protect against static but none of the 4-switch machines I own (4 currently) had it done. The 7800 does not have a 4050 in the design either, though it does have Zener diodes on each of the directionals along with filter capacitors. It's possible one of those has failed.

 

In any case, the OP will have to open it up to do any real further diagnostics. Sadly, most 7800's are not socketed so final diagnosis and repair will likely take some tools and skill. 

Got it. I fried my Hex buffer twice as a kid. I put the socket in the first time I repaired it. Still have that console. Never put it on the carpet after the second time as the static shock is what clued me into what happened the first time...

[+-^CrossBow^-]

50 minutes ago, Rick Dangerous said:

It's stuck like I'm pressing to the right constantly.

 

So it is repairable theoretically with some parts/soldering?

 

I just want to make sure it's not some unobtainable chip I would need. 

If it acts like you are moving the right constantly, then that would indicate the RIOT is most likely to blame. That is the large IC on the right hand side closest to the player 2 side controller port. @DrVenkman already mentioned it being possible, but that is also why I was asking if it was a directional issue or fire button issue as that tells us which of the main ICs is most likely to blame. 

 

Unless of course we are talking about the 2600 game side of things, in which case I believe the RIOT is the only chip in charge at that point.

 

 

[+DrVenkman]

8 minutes ago, -^CrossBow^- said:

If it acts like you are moving the right constantly, then that would indicate the RIOT is most likely to blame. That is the large IC on the right hand side closest to the player 2 side controller port. @DrVenkman already mentioned it being possible, but that is also why I was asking if it was a directional issue or fire button issue as that tells us which of the main ICs is most likely to blame. 

 

Unless of course we are talking about the 2600 game side of things, in which case I believe the RIOT is the only chip in charge at that point.

 

 

I mean, it's conceivable that there could be an issue with MARIA, SALLY or the SRAM causing code corruption, but in all cases (7800 or 2600) controller directions are read by RIOT, fire buttons and paddle lines are read by TIA. 

 

But by far the most likely cause is the RIOT, or one of the Zener diodes or caps on the lines. 

[Rick Dangerous]

Thanks for the input everyone! Going to have a professional attempt repair, thanks for pointing me in the right direction!