Bad Controller Ports - Atari 2600 JR

[kapsey]

I booted up my Atari 2600 JR the other day, and I found that both controller ports were unresponsive to any input from the paddles or joystick. I popped it open and took a peek at the board, and there’s no visible damage. 

 

I’m using the attached schematic and a multimeter to try and find the issue. I’ve tested C20 and L3 but they both work fine.

 

I suck at reading schematics. What components should I be focussing on to test? 

 

 

[+DrVenkman]

Paddles OR sticks? That’s not good. The joystick directionals are read by the 6532 RIOT chip, the paddle lines  and triggers are read by the TIA. It’s possible that you’ve got two bad chips but it’s not a common set of failures, I don’t think. At least not a likely set. I’ve had one 2600 with those two bad but the TIA mostly worked - I had some corrupted graphics, and so did the RIOT; the only thing not working there was the input from one of the difficulty switches.

 

That said, if you swap out the chips, start with TIA since it’s the main graphics and sound processor for the system - if your paddles start working, go ahead and see if your joystick work too - it’s possible the TIA has an internal short of some kind which is drawing down the +5V line on the controller ports and preventing them from working.

 

If chips swaps don’t work, it’s possible you’ve got a short - you say you’ve “tested” C20. How did you test it? 

[kapsey]

8 hours ago, DrVenkman said:

Paddles OR sticks? That’s not good. The joystick directionals are read by the 6532 RIOT chip, the paddle lines  and triggers are read by the TIA. It’s possible that you’ve got two bad chips but it’s not a common set of failures, I don’t think. At least not a likely set. I’ve had one 2600 with those two bad but the TIA mostly worked - I had some corrupted graphics, and so did the RIOT; the only thing not working there was the input from one of the difficulty switches.

 

That said, if you swap out the chips, start with TIA since it’s the main graphics and sound processor for the system - if your paddles start working, go ahead and see if your joystick work too - it’s possible the TIA has an internal short of some kind which is drawing down the +5V line on the controller ports and preventing them from working.

 

If chips swaps don’t work, it’s possible you’ve got a short - you say you’ve “tested” C20. How did you test it? 

I feel like the chips aren’t a likely failure because everything else works, and it just doesn’t sound too realistic that a bad chip would only affect the controller ports. It isn’t impossible, though.

 

You’ve got a good point though, and you also reminded me that I forgot to check to see if the ports were receiving power to begin with. I’m gonna do that when I get home, it’ll definitely narrow things down. 

 

As for C20, I desoldered it from the board and checked its resistance with a multimeter, which increased infinitely as it should. I know it’s not the most accurate way to check capacitors, but I don’t have any other tools. 

 

I’ll let you know if the ports are getting power once I test them. 

[+DrVenkman]

9 minutes ago, kapsey said:

I feel like the chips aren’t a likely failure because everything else works, and it just doesn’t sound too realistic that a bad chip would only affect the controller ports. It isn’t impossible, though.

 

Happens a lot more often than you realize. I've run into two bad RIOT chips. In each case, games worked and played fine so the system RAM worked as did the controller directional signals. But one - and ONLY one - difficulty switch didn't register. In one case it was the left player, in another it was the right player. That's a sure sign of static electricity damage - the shock traveled from someone's hand through the metal switch contact, down the trace and damaged just a small part of the IC. In both cases, replacing the RIOT fixed the issue.

Similarly, TIA damage can have the same effects - that chip in particular is relatively complex and handles a lot of duties - it reads a few inputs (paddles and trigger lines) so it's also subject to static. That part of the chip is not at all the same as the part that takes the kernel data from the 6507 and draws the screen and produce sound. 

 

Anyway, good luck with the troubleshooting. You might get more responses in the 2600 forum with other suggestions.

[+-^CrossBow^-]

Venkman is right... as sad as it is..the TIA is especially victim to ESD through the port pins it seems. As a result you can have everything looks great on the screen but then the TIA doesn't register controller movement properly. At least this is what is common on the 7800. On the 2600 as was stated, the RIOT handles controllers and I've had to replace a few of those over the years in many 2600s. 

 

The messed up thing here is that you are dealing with a Jr so your ICs are soldered in place and aren't as easy to remove out and swap anything with them.

 

[kapsey]

@DrVenkman @-^Cro§Bow^-

 

First off, thank you guys for all of your advice, I really appreciate it!!

 

I just fired it up again and the controller ports are receiving power, but now the graphics are messed up too. I’m gonna take your advice and try to replace those chips. I’ll let you guys know how it goes. Thanks again!!