By Kip Kiefer (MACE)
Michigan Atari Magazine, May 1988 Vol. 3, No. 5
Several years ago, I bought an Atari 800 parts kit (a non-working unit) and had it working within a few minutes. It had a bad voltage regulator and I had a replacement laying on my work bench, which explains the expedience of repair.
The only thing that still needed to be repaired was the keyboard. Half of the keytops were missing, a couple of the others weren't working. Since I wanted to use the computer right away, I found a cheap substitute keyboard at Radio Shack -- an Atari 1200XL keyboard (Cat.#277-1018).
Of course, it required a little work to wire it up to the computer. What's required is bringing the inputs of the 1200XL's keyboard encoder chips out to the adapter cable connecting the keyboard to the computer. Everything you need to do this can be found at Radio Shack. The following is a list of parts and tools you will need.
First the tools: (1) 25 watt soldering iron & solder; (1) solder wick, solder sucker or equivalent; (1) #0 Phillips screwdriver; (1) pair of wire strippers; (1) pair of diagonal wire cutters
Now for the parts: (1) Atari 1200XL keyboard part #ca060046 (Radio Shack #277-1018); (2) 16-pin low profile IC sockets (16-pin dip sockets); (2) 16-pin dip headers (no ribbon wires attached); (1) 5-foot piece of 25-conductor ribbon wire (Radio Shack #278-772); (1) pack "assorted" heat shrink tubing, (1) pair of mating connectors (with at least 22 pins). To make assembly easier, the instructions will be broken down into several parts.
Preparing the Keyboard
Place the keyboard face down on a table or work bench. Leave the keyboard in this position until its reassembly is completed. Don't start this project if you don't have the time to complete this section at one time. Remove the screws from the keyboard (qty: 21 screws). Lift the PC board off the keyboard. (Warning: Do not attempt to remove the plastic from the PC board, as this will damage the keyboard.) Using the soldering iron (and solder wick or solder sucker), remove the two 4051 IC chips (take note where pin #1 is.). Also remove the 15-pin connector (and wire). Solder the two 16-pin IC sockets in place of the two 4051 IC's that you've just removed. (Locate pin #1 of the IC socket in the same position as pin #1 of the 4051 IC chip.) Place the PC board on the keyboard and re-install the screws. You may turn the keyboard over now.
Making the Adapter Cable
To make it easier to understand, I'm going to call the two chips on the Atari 1200XL keyboard Al & A2. These aren't Atari's official part designations, but since I've never seen a parts list or a schematic for the 1200XL, they will do. In Fig. 1a, you will see the layout of the 1200XL keyboard bottom. The chart also shown in Fig. 1b shows the equivalent chips for the other models. In Fig. 2, you'll see the connections required to connect the 1200XL keyboard to your computer. The two 16-pin dip headers plug into the IC sockets that you've installed; you will be soldering wires onto the dip headers and the keyboard connector pads per Fig. 2. I'll let you decide which kind of connector you wish to use.
One tip is to wire the adapter cable so the connector (mounted on the computer case) pin connections match your computer keyboard's connections. This will keep your connections more straightforward. The best place to mount a connector for the keyboard on a Atari 400 or 800 is on the left side of the computer (the side opposite the power connector).
This is how I did it. Being somewhat of a scavenger at heart, what I used for connectors was somewhat different than their normal application.
I used a 22-pin Cinch (double-sided) edge connector (wired to the computer keyboard connector per Fig. 3) and a single-side PC (Printed Circuit) Board completed the connection. The PC board is cut short per Fig. 4. If you're wiring the keyboard per the chart in Fig. 3, your keyboard should look like Fig. 5 when you're done.
Figure 6 shows the Cinch connector as viewed from the rear. Figure 7 shows how to dress the wires from the 1200XL keyboard. The reason I wired the connector in the manner I did (per Fig. 3), was so I wouldn't have to worry about the connector's polarity (you can plug it in either way and it works the same), which may make the routing of the keyboard cable easier.
[Figure 9 shows the layout of the top "function key" row of the 1200XL, and also the standard pin numbering of DIP chips. - RMF]
The Way I Didn't Tell You About
The reason that I didn't tell you about this last way of connecting the 1200XL keyboard is that it has the least amount of options. You can only have the 1200XL keyboard operational (not the original keyboard or a optional keypad). An additional drawback to this method is the increased possibility of shorting out the 5-volt power supply. It requires the removal of the computer's keyboard encoder chips, and the adapter cable will run from the 1200XL keyboard connector to two 16-pin dip headers plugged into the computer's keyboard encoder chip sockets (see Fig. 8).
I do not recommend using this last method of connecting the keyboard to your computer. Although it would put your computer into the same configuration as the 1200XL, the drawbacks outweigh the benefits.
