Atari 800 keyboard chip

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I have an Atari 800 with keyboard that is not responding at all. I tried another keyboard - same issue.

The issue is not with a keyboard - must the motherboard or the chip that controls the keyboard.

 

What would you check first? Computer otherwise boots fine. Start/Select/Option/Reset buttons appear to work.

[CZroe]

I have an Atari 800 with keyboard that is not responding at all. I tried another keyboard - same issue.

The issue is not with a keyboard - must the motherboard or the chip that controls the keyboard.

 

What would you check first? Computer otherwise boots fine. Start/Select/Option/Reset buttons appear to work.

The 4021 shift register/encoder chips are known to fail but they don't usually fail completely. In my case I had many bad keys and some good keys. Switching the two 4021 chips around switched the good/bad keys around. The replacements were so cheap that I didn't even bother figuring out if one chip was still good (just replaced both and have 4021s to spare).

[BillC]

The 4021 shift register/encoder chips are known to fail but they don't usually fail completely. In my case I had many bad keys and some good keys. Switching the two 4021 chips around switched the good/bad keys around. The replacements were so cheap that I didn't even bother figuring out if one chip was still good (just replaced both and have 4021s to spare).

The multiplexer/demultiplexer chips used for the keyboard are 4051, not 4021!

[[email protected]]

Thanks, I will start the search for the 4051 chips.

[CZroe]

The multiplexer/demultiplexer chips used for the keyboard are 4051, not 4021!

Thanks. Looks like I was copying an old typo after I skimmed my old thread.

 

Edit: actually, I looked it up, saw "4051," and then wrote "4021" anyway because I'm also familiar with the NES controller shift register.

Edited October 26, 2017 by CZroe

[+slx]

If it still doesn't work after changing the 4051s (mine didn't ) and your keyboard is a Mitsumi, there's a repair video here.

[Paul Westphal]

^{Best electronics has the chips but he has a $20 minimum order. Mouser does too.}

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The keyboard itself is fine - I pulled a keyboard from a working 800 and installed it on the defective motherboard - the working keyboard did not respond.

I'll buy the 4051 on ebay - this should work?

 

https://www.ebay.com/p/Texas-Instruments-CD4051BE-Multiplexer-8-Channel-16dip/1200436875?iid=282437169279&_trkparms=aid%3D222007%26algo%3DSIM.MBE%26ao%3D2%26asc%3D48740%26meid%3Db77ae6b4c40a4497aedc2fb862fea0bf%26pid%3D100005%26rk%3D1%26rkt%3D6%26sd%3D322795851890&_trksid=p2047675.c100005.m1851