Atari 400 "+" key stuck. Keyboard or other hardware issue?

[Skippy B. Coyote]

Hey there lovely people. I just got my first classic computer in the mail today, an Atari 400, and it worked great for about 2 hours. However a problem soon arose that I could use some advice on. The problem is that the all of a sudden the computer thinks the + key is being held down, so when I load Atari BASIC or just boot into the built in notepad application with no cartridge inserted all I get is a continual stream of + symbols and can't enter any other inputs.

 

The strange thing is that if I power the computer off and leave it alone for 10 minutes or so then come back and power it on everything works as normal again about half the time, including the + key. I can press the + key all I want and can't make it stick again, but after a few minutes of use it will go back to thinking the + key is held down even if I don't touch the keyboard at all.

 

So what I'm trying to figure out is whether the keyboard needs to be replaced (which would be quite unfortunate since I blew all my discretionary funds for the month on the computer itself and wouldn't be able to afford to replace the keyboard until at least next month) or whether this could be an issue with another piece of hardware in the computer. I've read that the POKEY chip is responsible for interpreting all the keyboard inputs in the Atari 400, so is it possible that a failing POKEY chip might create an issue like the computer thinking a key is being held down when it isn't?

 

Any advice on this matter would be greatly appreciated.

[+x=usr(1536)]

Hey there lovely people. I just got my first classic computer in the mail today, an Atari 400, and it worked great for about 2 hours. However a problem soon arose that I could use some advice on. The problem is that the all of a sudden the computer thinks the + key is being held down, so when I load Atari BASIC or just boot into the built in notepad application with no cartridge inserted all I get is a continual stream of + symbols and can't enter any other inputs.

 

The strange thing is that if I power the computer off and leave it alone for 10 minutes or so then come back and power it on everything works as normal again about half the time, including the + key. I can press the + key all I want and can't make it stick again, but after a few minutes of use it will go back to thinking the + key is held down even if I don't touch the keyboard at all.

 

So what I'm trying to figure out is whether the keyboard needs to be replaced (which would be quite unfortunate since I blew all my discretionary funds for the month on the computer itself and wouldn't be able to afford to replace the keyboard until at least next month) or whether this could be an issue with another piece of hardware in the computer. I've read that the POKEY chip is responsible for interpreting all the keyboard inputs in the Atari 400, so is it possible that a failing POKEY chip might create an issue like the computer thinking a key is being held down when it isn't?

 

Any advice on this matter would be greatly appreciated.

 

Unplug the keyboard, let it sit for the amount of time that it takes for the '+' key to stick, plug the keyboard back in, and see what happens. From memory, you should be able to hotplug the keyboard without any adverse effects, but someone should double-check me on this since it's been a couple of decades since I last had a 400 open.

 

If the problem recurs, it's possibly (note the conditional) not the keyboard.

 

If it doesn't, plug the keyboard back in, make sure that everything is securely connected, and see what happens.

 

This should at least give you some ideas of where the problem might be. Good luck!

Edited April 7, 2018 by x=usr(1536)

[Skippy B. Coyote]

Thank you for the advice x=usr(1536)! I did some troubleshooting as recommended and made a little video of the issue so you can see what's going on for yourself, and I think it's fairly safe to say that the problem is indeed with the keyboard and not any other components. I'll be calling up Best Electronics to order a new keyboard as finances allow.

 

https://www.youtube.com/watch?v=ptcgOa0RR7c

[Kyle22]

It could also be the 4051 decoders. These chips are cheap.

Try them before spending $15 or $20 for a new PoKey

[+tf_hh]

Hey there lovely people. I just got my first classic computer in the mail today, an Atari 400, and it worked great for about 2 hours. However a problem soon arose that I could use some advice on. The problem is that the all of a sudden the computer thinks the + key is being held down, so when I load Atari BASIC or just boot into the built in notepad application with no cartridge inserted all I get is a continual stream of + symbols and can't enter any other inputs.

 

The strange thing is that if I power the computer off and leave it alone for 10 minutes or so then come back and power it on everything works as normal again about half the time, including the + key. I can press the + key all I want and can't make it stick again, but after a few minutes of use it will go back to thinking the + key is held down even if I don't touch the keyboard at all.

 

I´m pretty sure that the keyboard itself is the problem. If POKEY or the 4051 mux chips would be the source of trouble, then at last one row of keys won´t work - but you told, in the "good phase" all keys are working fine.

 

The 400 keyboard is extremly simple and cheap made of glued mylars. I don´t know any way to fix it, only a replacement keyboard (BEST Electronics oder MyAtari) will help.