So with the video connection in place, I powered the Atari up again to see the default memo pad program that comes preloaded into ROM. I typed out my first memo, "Hello world!" and looked up to see "hoo" after the prompt. After testing all of the keys, the only ones I found to be working were 'h', 'a', 'o', '9' and 'break'.
Getting to the keyboard of the 800 is fairly straightforward but it's important to keep track of parts as it requires some disassembly. The first step is to remove the bottom part of the case. Flipping the computer over exposes the five screws that hold the bottom half of the plastic casing to the top. After removing these screws, slide your fingernails into the joint between the halves of the casing on the backside (TV cable side) of the box and pry the halves apart. It's important to start on the back because the joystick ports in the front protrude from the casing and make it difficult to remove the front first. Now the only thing attaching the bottom cover should be a pair of wires connecting the speaker to the main board. The speaker is permanently attached to the red kill switch on the bottom cover so disconnect the wires and put the lower cover and speaker aside.
Now to remove the main board. There are four screws, identical to those you just removed holding the board to the upper cover. The two on the right side (where the auxiliary ports and power supply are) go through the aluminium casing. The left two go through the main board. Remove all of them and slowly lift the front of the board. The last connection will be a ribbon of wires running from the keyboard assembly into the main board.
Carefully record their orientation and remove the wires. Now you can slowly remove the main board assembly and put it aside. All that should remain is the keyboard attached to the upper cover. Finally, to extract the keyboard, remove the four screws securing it to the case and gently pull it away.
The keyboard has three components. The key assembly is purely mechanical and has no electronic components. Problems with the keys should be fairly obvious. To detach it, remove the dozen or so small screws and it should come off easily. One of the screws is positioned under the wires that connect the keyboard to the main board. On my Atari these wires were stuck to the back of the keyboard with double sided tape. If this is the case with your box as well, simply use a razor blade to peel the tape from the back of the keyboard to access the last screw.
If all the keys depress and there is no visible malfunction you can put this part aside for now. You're left with a a printed circuit board onto which is taped a sheet of Mylar.
The underside of the Mylar is covered in electrical connections that have been painted on with conductive paint. When a key is pressed a contact point on the Mylar is pushed into a contact point on the PCB and a unique connection is made. Often, the conductive paint can crack or chip which leads to broken connections and faulty keys. In order to check the Mylar, it must be removed very carefully. First, the electrical tape must be removed, care being taken not to tear the delicate Mylar. Next the Mylar can be slowly peeled off the PCB. It's likely that the keyboard was never serviced so the Mylar will stick to the PCB, especially around the screw holes. Be patient - the last thing you want to do is tear the Mylar.
With the Mylar fully removed, you can inspect for cracks. If you don't see anything, it's time to take out the multi-meter. There are eight strips at the bottom of the Mylar where the conductive ink makes contact with the PCB. Each of these is at the head of a trail of nodes on the Mylar. To test a strip, simply place one terminal of the multi-meter at the strip and the other at the furthest connected node - if there's a fork in the trail, test all of the ends. In this manner you should be able to quickly test all of the connections on the Mylar. If you do find a break, it's a quick fix. Just pick up some conductive paint at your local electronics store (RadioShack sells this) and carefully paint over the break.
If you were unable to find a break, the adventure continues. Another point where the connections tend to break is the contact point between the Mylar and the PCB.
The conductive strips on the Mylar need to be pressed firmly into the terminals on the PCB. There is a ridge on the button assembly that is supposed to do keep the two layers firmly connected but this can fail over time.
In fact, this is what ended up being wrong with my keyboard. The easy fix here is to add a strip of electrical tape on the top side of the Mylar, right above the connections. This makes the whole assembly a little thicker and makes ensures that the Mylar is sandwiched more tightly to the PCB.
With the new tape job in place I reassembled the keyboard for a quick test and voila!
It worked!
Getting to the keyboard of the 800 is fairly straightforward but it's important to keep track of parts as it requires some disassembly. The first step is to remove the bottom part of the case. Flipping the computer over exposes the five screws that hold the bottom half of the plastic casing to the top. After removing these screws, slide your fingernails into the joint between the halves of the casing on the backside (TV cable side) of the box and pry the halves apart. It's important to start on the back because the joystick ports in the front protrude from the casing and make it difficult to remove the front first. Now the only thing attaching the bottom cover should be a pair of wires connecting the speaker to the main board. The speaker is permanently attached to the red kill switch on the bottom cover so disconnect the wires and put the lower cover and speaker aside.
Now to remove the main board. There are four screws, identical to those you just removed holding the board to the upper cover. The two on the right side (where the auxiliary ports and power supply are) go through the aluminium casing. The left two go through the main board. Remove all of them and slowly lift the front of the board. The last connection will be a ribbon of wires running from the keyboard assembly into the main board.
Carefully record their orientation and remove the wires. Now you can slowly remove the main board assembly and put it aside. All that should remain is the keyboard attached to the upper cover. Finally, to extract the keyboard, remove the four screws securing it to the case and gently pull it away.
The keyboard has three components. The key assembly is purely mechanical and has no electronic components. Problems with the keys should be fairly obvious. To detach it, remove the dozen or so small screws and it should come off easily. One of the screws is positioned under the wires that connect the keyboard to the main board. On my Atari these wires were stuck to the back of the keyboard with double sided tape. If this is the case with your box as well, simply use a razor blade to peel the tape from the back of the keyboard to access the last screw.
If all the keys depress and there is no visible malfunction you can put this part aside for now. You're left with a a printed circuit board onto which is taped a sheet of Mylar.
The underside of the Mylar is covered in electrical connections that have been painted on with conductive paint. When a key is pressed a contact point on the Mylar is pushed into a contact point on the PCB and a unique connection is made. Often, the conductive paint can crack or chip which leads to broken connections and faulty keys. In order to check the Mylar, it must be removed very carefully. First, the electrical tape must be removed, care being taken not to tear the delicate Mylar. Next the Mylar can be slowly peeled off the PCB. It's likely that the keyboard was never serviced so the Mylar will stick to the PCB, especially around the screw holes. Be patient - the last thing you want to do is tear the Mylar.
With the Mylar fully removed, you can inspect for cracks. If you don't see anything, it's time to take out the multi-meter. There are eight strips at the bottom of the Mylar where the conductive ink makes contact with the PCB. Each of these is at the head of a trail of nodes on the Mylar. To test a strip, simply place one terminal of the multi-meter at the strip and the other at the furthest connected node - if there's a fork in the trail, test all of the ends. In this manner you should be able to quickly test all of the connections on the Mylar. If you do find a break, it's a quick fix. Just pick up some conductive paint at your local electronics store (RadioShack sells this) and carefully paint over the break.
If you were unable to find a break, the adventure continues. Another point where the connections tend to break is the contact point between the Mylar and the PCB.
The conductive strips on the Mylar need to be pressed firmly into the terminals on the PCB. There is a ridge on the button assembly that is supposed to do keep the two layers firmly connected but this can fail over time.
In fact, this is what ended up being wrong with my keyboard. The easy fix here is to add a strip of electrical tape on the top side of the Mylar, right above the connections. This makes the whole assembly a little thicker and makes ensures that the Mylar is sandwiched more tightly to the PCB.
With the new tape job in place I reassembled the keyboard for a quick test and voila!
It worked!
Thanks for your post. The problem you experienced is the same as what I experienced on my 800. The remedy was also the same. My disassembly was slightly different, probably due to product changes as my unit may have been slightly newer. I only had 3 screws to remove inside the case, and my keyboard cable was a ribbon cable, making the disassembly and reassembly slightly easier.
ReplyDeleteThanks!
I'm glad you found it useful!
ReplyDeleteThanks! Your post helped me fix my Atari 800 keyboard. It needed conductive paint. It's working great now.
ReplyDeleteThanks a LOT! My 800 keyboard initially had only two working keys. The problem turned out to be needing extra pressure on the conductive connection between the mylar and the keyboard assy - as you experienced. I used a couple of layers of electrical tape to increase the pressure as you suggested and now my keyboard works perfectly!
ReplyDeleteThanks so much for this, helped me get my keyboard out of my newly-acquired 800 with no dramas!
ReplyDelete