Keyboard ribbon connection problems

[llopis]

I have this 464 that works great apart from some keys not working (2, 3, 5, 7, 9, -=, [, and right, along with [, numpad 4, SHIFT, and \). It turns out they're the ones corresponding to the bit 4 plus also the ones in row corresponding to pin 17 (except that ENTER works for some reason).


I tried the keyboard on another 464 and it worked fine there. All the keyboard pins connect to the right pins in the AY and 74LS145 chips.


That makes me think that the keyboard connector isn't having a good connection with the ribbon from the membrane. I gave the PCB connector an extra scrubbing with a toothbrush and alcohol, and then another column stopped working. Clearly we're in the right track :-)


So I'm wondering what the best way to clean the keyboard connector is. Is there something more thorough to improve connection with the ribbon?

[llopis]

I cleaned it up really well, including the keyboard ribbon leads, try it again, and now only 7 and -= fail, which is not even a full column. What's going on? I can't imagine it's part of the PCB because I'm not touching that.

[robcfg]

Maybe it's the AY or LS145 chips that are wrong.


I don't know if there's an easy way to check them without desoldering.

[llopis]

Maybe it's the AY or LS145 chips that are wrong.

Do you think the behavior would change just by unplugging/cleaning/plugging the ribbon cables if it was a bad IC? Behavior never changes otherwise (turning computer on and off multiple times).

[robcfg]

Just out of curiosity, have you tried the other 464's keyboard on the faulty connector?

[llopis]

Just out of curiosity, have you tried the other 464's keyboard on the faulty connector?

Haha I haven't! The other 464 is just a PCB :-b

[robcfg]

Hehe, ok!


But you can still try to put the other pcb in your 464 case and test it.

[llopis]

But you can still try to put the other pcb in your 464 case and test it.

Yes, that's what I described in a post above: I hooked up the keyboard to the space PCB and it worked fine. That's what made me think it was the connectors on the board itself.


I gave them a super-good cleaning with alcohol and a toothbrush last night. I also re-flowed the solder on the connector. It looked OK, but they had some wobble to them.


Now it looks like it's working, but we'll see if it stays that way or it changes soon. I won't be touching the cables in the meanwhile just to see :-)

[llopis]

For those of you following along:
- I scrubbed the keyboard ribbon connector with alcohol. It seemed to make it better at times, but usually a few keys would still miss (same column).
- I scrubbed it with contact cleaner. Same results. Once they all worked, and then the following day a few keys were missing again.
- Every time I moved the keyboard to another PCB, it worked without a hitch.
- I even checked to see if it was a bend in the keyboard ribbon since in one case I was trying it on a case and in another case on a plain PCB. Nothing.
- I checked every continuity between the keyboard connectors and the AY and 74LS145 chips. Everything was good.


Eventually I convinced myself it had to be one of those two chips (probably the AY since column 2--keyboard connector 4--was the one that was consistently having issues). I pulled it out, put it on a socket, tried it again with the same chip, and same problems. Now, without even removing the ribbon cable, I swapped it for a new AY chip, and it worked flawlessly 


This is not the first time I encounter an AY chip that acts in erratic ways. I guess they're somewhat failure-prone for some reason.

[Bryce]

The AY is known for failing on the digital side, which is strange because the technology was well developed and understood by the time the AY was developed, so there's no real excuse for it.

Bryce.