Atari XE Game System Keyboard Repair

Inside the XE Game System keyboard: the small board marked KEYBOARD SUB PCB, with the membrane's flat cable running into its connector (photo: "Sleeπ" for Best Electronics)

The Atari XE Game System (XEGS) has a detachable keyboard that plugs into the left side of the console through a 15-pin D connector. Matthew Ratcliff, who examined the console for Antic in 1988, found the keyboard virtually identical to the Atari 130XE's, with a small circuit board inside carrying resistors, capacitors and two CD4051 chips that decode the key presses and send them to the POKEY chip in the console. The steps below find a dead key with Atari's self test and a meter, then open the keyboard and renew its contacts, following Best Electronics' instructions, which were written for the XE Game System keyboard.

Symptoms

• One key, or a group of keys, does nothing in BASIC or in the self test's keyboard test.
• A key works only sometimes. Sams' service data for the 130XE keyboard gives cleaning the key as the remedy for an erratic key.
• The console starts Missile Command with the keyboard plugged in. With a keyboard connected the XEGS loads BASIC at switch-on, unless SELECT is held down.

START, SELECT, OPTION and RESET are on the console itself, so a fault in one of those four keys lies in the console.

Safety

• Switch the console off before connecting or disconnecting the keyboard. Turn it off and disconnect all the cables before opening the keyboard.
• Handle the flexible flat cable from the membrane with care; Best warns that pulling the membrane out at an angle can tear or crease it.

Tools and parts

• Phillips #0 and #1 screwdrivers, a flat screwdriver and tweezers.
• Latex gloves. Best's author wears them to keep sweat off the flat cable and fingerprints off the metal parts.
• A meter with a resistance range.
• Replacement silicone contacts, if the old ones no longer conduct. Best Electronics sells them as its "XE Touch" set.

Procedure

1. Run the keyboard test

1. With the keyboard connected, hold OPTION and switch on to reach the self test, choose KEYBOARD with SELECT and start it with START.
2. Press each key. The matching key on the screen keyboard flashes and a note sounds. The space bar and the function keys are already shown in reverse video, so they flash in normal video, and SHIFT and CONTROL flash only when pressed with another key.
3. Note every key that does not respond. HELP, RESET and BREAK cannot be tested: HELP returns to the self-test menu and RESET leaves the test.

2. Open the keyboard

The underside of the XEGS keyboard with its eight case screws circled (photo: "Sleeπ" for Best Electronics)

1. Disconnect the keyboard from the console and lay it with the keycaps facing down. Remove the eight screws from the bottom case.
2. Holding the two halves together, turn the keyboard over so the keycaps face up, and lift the grey top cover off the bottom case.
3. Lift the keyboard assembly carefully at its upper right edge with a flat screwdriver.
4. Pull the flexible flat cable evenly out of the board's black pinch connector. Best finds this easier with a helper holding the bottom case, and warns against pulling the membrane out at an angle.

3. Test the keys at the membrane connector

The XE keyboard matrix. Each key joins the two lines it sits on, and the line numbers are the pins of the membrane connector J8 (JER/Eightbitter's redraw)

The keys form a matrix. In JER/Eightbitter's redraw, each key sits where one of the lines 13, 14, 12, 15, 7, 18, 5 and 6 crosses one of the lines 19, 4, 8, 9, 10, 11, 17, 16 and 20, and the line numbers are the pin numbers of the membrane connector J8.

1. Find the faulty key on the matrix and note its two J8 pins.
2. Put the meter across those two pins at the membrane's flat cable and press the key. Sams gives about 55 Ω for a good key on the 130XE keyboard, which Ratcliff found virtually identical to this one.
3. If every key on one line fails, suspect that line of the membrane or its contact in the connector.
4. If a key does not read at all, open the keyboard further and renew its contact (steps 4 to 6).

4. Take out the membrane

The metal bottom plate, with the small screws that hold it circled (photo: "Sleeπ" for Best Electronics)

1. Remove all the small screws from the metal bottom plate and keep them together.
2. Lift off the metal plate, then lift out the double-layer membrane.
3. Inspect the membrane traces. For damaged traces on the near-identical XE computer keyboards, see Atari 65XE Keyboard Repair.

The plate lifted off, with the double-layer membrane still in the top housing (photo: "Sleeπ" for Best Electronics)

5. Renew the contacts

1. Turn the top housing over and the old silicone contact cups fall out.
2. On the XE Game System keyboard four white plastic plungers, from the four top function-key positions that this keyboard does not use, also drop out. Put them back in their cavities in the top shell.
3. Rest the top case on two supports, such as books, so that the keycaps, now facing down, do not touch the table.
4. Fit the new contacts where the old ones were, black dot facing up, including the four unused function-key positions.

Replacement contacts going into the key positions of the top housing, black dot up (photo: "Sleeπ" for Best Electronics)

6. Reassemble

1. Lay the membrane on the inside of the top case, locating it on its two plastic pins.
2. Refit the bottom plate. Before tightening each screw, turn it gently anticlockwise until you feel a light click, then tighten it. Best warns that otherwise each screw cuts a new thread and after several rebuilds no longer holds.
3. Reverse the rest of the disassembly, reconnecting the flat cable evenly.

7. If the membrane tests good

The keyboard's own circuit in JER/Eightbitter's redraw: J8 at the top, R1 to R17, the 4051 multiplexers U1 and U2, and the plug J10A on the cable

The keyboard's board carries the multiplexers. In JER/Eightbitter's redraw of the XEGS, J8 pins 17, 11, 8, 16, 19, 10, 4 and 9 run through R9 to R16 to the inputs of one 4051 (U1), and pins 18, 13, 15, 5, 14, 6, 12 and 7 through R1 to R8 to the other (U2). The seventeen resistors R1 to R17 are marked 270 Ω. J8 pins 1 to 3 and 21 to 24 are drawn unconnected; on the XE matrix, lines 2 and 3 carry the power LED, and line 3 with lines 21 to 24 the console keys. The keyboard reaches the console through the 15-pin plug J10A.

1. Check the resistor on the line of a dead group of keys.
2. Check the keyboard cable and its 15-pin plug, which Ratcliff describes as a standard DB15.
3. The board-side checks on the XE computers, which use the same POKEY keyboard scan with their multiplexers on the main board, are in Atari 130XE Keyboard Repair.

Testing

1. Connect the keyboard with the console switched off, then switch on. The console should load BASIC.
2. Run the keyboard test again and press every key.

Board revisions

The pin and part numbers above come from JER/Eightbitter's 2016 redraw, which is not an Atari document. Best's photographs show a board marked KEYBOARD SUB PCB, but they are too small to read its part designators.

Related pages

• Atari XE Game System
• Atari XE Game System Troubleshooting Guide
• Atari XE Game System General Maintenance
• Atari XEGS Mods & Upgrades
• Atari 65XE Keyboard Repair
• Atari 130XE Keyboard Repair