Atari 400 keyboard: Ctrl/Shift/Break not working

[hoserama99]

Hi all,

 

I recently got my first Atari 8-bit computer, a 400 with what I now understand is a "B-key" mod. That's all fine, but I really wanted the membrane experience just because it's weird and cool, so I bought one off eBay that was "as-is".

 

As you can maybe guess from the subject, it's a little wonky: the ctrl, shift and break keys do not seem to register. Looking at the keyboard matrix for the 400, it looks like these keys are all common to pin 9. Easy fix! Except it's not: this weird and cool keyboard is sealed up tight, and I can't see an easy way to get at the traces.

 

I suspect I'm out of luck, but I'm open to suggestions on how I might get in there to make a repair, as I'm not really in the mood to buy yet another membrane keyboard since the B-key I have does work, even if it's not as interesting.

 

I did try to look at the Best Electronics and myatari websites but I think it might be easier to just unglue the membrane keyboard than try to navigate those sites: Best doesn't list any Atari 400 keyboards that I can see, and the B&C/myatari site just says everything is "offline" since mid-2018.

[+Nezgar]

B&C/myatari definitely has 400 membranes. Just email and ask for a quote. I 'almost' bought one from him last year, but decided the existing was good enough that a thorough cleaning should be sufficient considering the cost of his replacement. He told me he removed the pricelist because he was too overloaded to keep it up to date.

 

Price I was quoted in August 2018:

PRA002 KEYBOARD 400 MEMBRANE NEW - $39.95

 

With that said, sorry I don't actually have experience servicing a 400 keyboard yet...

[hoserama99]

Thanks for that info. $40 is a bit steep considering that's what I paid for the unit itself. I'll have to think on that.

 

I'm starting to warm up to the notion that maybe I won't ever actually need to press the ctrl, shift or break keys although I honestly don't know if I could actually live without them given I know so little about 8-bit Atari computers. I love the look of that membrane so much that I'm wondering how much I'll sacrifice.

[Kyle22]

You *WILL* need those keys to work.

 

Edit: unless you're just playing games and not doing anything productive.

Edited June 6, 2019 by Kyle22

[Urchlay]

You sure the trace inside the membrane sandwich is at fault? It might

just need cleaning at the connector. I'd definitely try that first

(just use 92% isopropyl alcohol, or something like Deoxit).

 

Or... If you're not going to upgrade the RAM, you'll probably end up

using the 400 just for cartridge games. Most of those would be fine

without control, shift, or break.

[Rybags]

You could also try swapping over the 2 x 4041 multiplexor ICs - if one is faulty then the symptoms should change. And the act of swapping them should be sufficient to deoxidize the pins and contacts.

[+slx]

You *WILL* need those keys to work.

 

Edit: unless you're just playing games and not doing anything productive.

 

Doing anything productive with a 400 membrane keyboard would be quite heroic.

[+slx]

I recently needed something from myatari that wasn't listed on Ebay and just contacted him through Ebay messaging. I got a prompt reply.

[+mytek]

You could also try swapping over the 2 x 4041 multiplexor ICs - if one is faulty then the symptoms should change. And the act of swapping them should be sufficient to deoxidize the pins and contacts.

To add to this... if you have a spare Pokey, try swapping that in case the KR2 input is dead. Or simply remove and replace the original Pokey in case it's pins have oxidized. KR2 is responsible for acknowledging CTRL, SHIFT, and Break.

 

And lastly, since that is a single line from the keyboard back to the KR2 pin, if the membrane connection is broken it might be possible to locate and repair it using some conductive paint.

[hoserama99]

You sure the trace inside the membrane sandwich is at fault? It might

just need cleaning at the connector. I'd definitely try that first

(just use 92% isopropyl alcohol, or something like Deoxit).

 

 

I'm reasonably sure it's the membrane as all keys work when the B-key keyboard is installed. For that reason, I haven't done any further diagnostics on the motherboard.

 

I used alcohol to clean the membrane connector but you're right: I should clean the motherboard connector too just to be safe.

[hoserama99]

To add to this... if you have a spare Pokey, try swapping that in case the KR2 input is dead. Or simply remove and replace the original Pokey in case it's pins have oxidized. KR2 is responsible for acknowledging CTRL, SHIFT, and Break.

 

And lastly, since that is a single line from the keyboard back to the KR2 pin, if the membrane connection is broken it might be possible to locate and repair it using some conductive paint.

 

I don't have a spare pokey but I'm reasonably sure it's OK as the keys work when the B-key keyboard is installed. I suppose I could try reseating the Pokey too, but I'm not sure if it's socketed (I haven't looked in detail).

 

I did look on the membrane at the traces in the connector and didn't see anything obviously broken. The difficulty here is that the connector seals them all up in a thick transparent plastic so they're pretty hard to get at without really invasive surgery, I think? I'm hoping for some tips to actually remove (and eventually reglue) the membrane cover but I gather that most people just replace it rather than bother with all that.