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PET 4032 keyboard stuff

A

azog

Experienced Member
Joined
Apr 19, 2004
Messages
127
Location
New Jersey
Been trying to revive a PET 4032. As far as I can tell, the only major issue is with the keyboard.

The first step was to completely disassemble the keyboard to completely clean it out, and boy was it grubby.

But there is/was a lot of crud on the system board, and all of the problem areas seem to be directly over the keyboard driver circuits. Here are some blog entries with photos:

First assessment: http://www.azog.org/?p=833
Crud on the motherboard: http://www.azog.org/?p=900
Cleaning the motherboard: http://www.azog.org/?p=911

If you've not had the patience to follow my progress, the long and the short of it is that I've had to remove the resistor pack, a 74LS145 and the keyboard connector to be able to clean some of the crud underneath. I replaced the DIP packages with brand-new components, but re-used the male header. I might eventually go back and remove that, as some of the posts have nasty pitting on them, which may affect connectivity. But in the meanwhile, I can beep out all connections between the keyboard connector and the various points on the board, so electrically everything is sound.

My next step is to work on the actual keyboard connector. The corrosion was more damaging here, as several of the pins inside the female 1x20 connector have been eaten away and the wires are either in the process of breaking off, or have already broken off. I don't have any photos of this (yet), so I'm looking at replicating the connector cable between the keyboard and the motherboard.

It appears the card-edge connector on the keyboard side is in good condition, so I'm down to trying to find, or build a 1x20 cable, which brings me to the ultimate purpose of my post.

Does anyone know where to find, or perhaps even have a connector that's already wired? I can deal with the card-edge connector, since that's just a punch-down type, so I don't care what's on the other side, it's just the female 1x20 connector that's vexing me right now.

As a just-in-case scenario, the last thing to do would be to replace the 6520. I'm wary of trying to remove it intact, for fear of damaging the board itself, which is why I would opt to just destructively remove it. If I can find a 6520, I'll socket it, and at the very least, it'll replace the final component in the keyboard driver.
 
Recently I thoroughly cleaned the keyboard in my perpetually illin' 4032, and, well... I wouldn't be completely confident that at least part of your problem isn't just the rubber contacts in the board. I cleaned out mine well, and most of the keys worked decently immediately after I deemed it dry enough to reassemble and test. But after just a few days the keyboard started being much less responsive. It's almost as if the little black pads soaked up enough water to temporarily rejuvenate them, only to have the good done literally evaporate after a while. I'm considering attempting to dab a little conductive paint on them.

Depending on where you live 6520's aren't hard to find. Coincidentally enough I literally picked two up on the way into work this morning for $1.95 each. 6522s seem to be rarer/more in demand. I got mine from here:

http://www.anchor-electronics.com/
 
azog said:
...Does anyone know where to find, or perhaps even have a connector that's already wired? I can deal with the card-edge connector, since that's just a punch-down type, so I don't care what's on the other side, it's just the female 1x20 connector that's vexing me right now.
Click to expand...
Why not just use a 40-pin IDE cable & connector and punch down every alternate wire at the KB end?

As a just-in-case scenario, the last thing to do would be to replace the 6520. I'm wary of trying to remove it intact, for fear of damaging the board itself, which is why I would opt to just destructively remove it. If I can find a 6520, I'll socket it, and at the very least, it'll replace the final component in the keyboard driver.
Click to expand...
I'd try manually bridging pins on the KB connector first to simulate keypresses before I looked at the 6520.
 
MikeS said:
Why not just use a 40-pin IDE cable & connector and punch down every alternate wire at the KB end?

I'd try manually bridging pins on the KB connector first to simulate keypresses before I looked at the 6520.
Click to expand...

And such is why I posted here! After staring at an annoying problem for a period of time, you loose sight...

Since the cable is now at the point of no return, I'll try your suggestion to bridge the pins to make sure I get all the key responses. As I mentioned, I'm pretty sure the 6520 is NOT the problem, I'm betting it's all mechanical. The only reason I would remove it is to clean under it.
 
I'll just chime in that last night I cleaned up the keyboard of my newly-acquired 4016. (It had dead spiders in it. Eeeek.) I pulled the little rubber contact pads out of the plungers but otherwise left the key mechanism part intact while washing it in a dishpan of warm soapy water, and while that was drying I separately washed the board and contact pads with alcohol and hit the contact pads on the board with a white pencil eraser. Aaaand... based on a comment in another thread about graphite I tried an experiment: After putting the dried contacts back into the keyboard assembly I took a newly sharpened 6B art pencil and gently stroked the side of the lead across each black pad, after which I dabbed any loose powder up by touching the pad with a swab lightly soaked in alcohol.

The graphite pencil part might just of been black magic/not a good idea, but for now it seems to be working great, better than the 4032 keyboard I merely cleaned.
 
Which is more disgusting to find inside an old computer: dead spiders, rat droppings or fungi? I think I've seen all three, although probably not inside the same machine.
 
carlsson said:
Which is more disgusting to find inside an old computer: dead spiders, rat droppings or fungi? I think I've seen all three, although probably not inside the same machine.
Click to expand...

Along with rodent droppings I found a mummified mouse in one of my acquisitions.

Tez
 
The dead mouse wasn't so bad. More alarming were three huge live cockroaches which hitched a ride inside an IBM AT I got from Auckland. Auckland is warmer than where I live and cockroaches of that size, while they may be common there, are NOT common in cooler Palmerston North.


Hopefully I got all the hitchhikers. I was so paranoid I even laid some traps around and in the computer shack but they came up empty.

Tez
 
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