Atari 65XE Keyboard Repair

Jerzy Sobola's drawing of the 65XE keyboard matrix. Each line carries the number of its pin on the keyboard connector J8; a key joins the column and row it sits on

The keyboard of the Atari 65XE is a matrix of key switches wired to the main board through the 24-pin keyboard connector J8. POKEY (U22) scans it through two CD4051 multiplexers, U24 and U25, the same arrangement as on the Atari 130XE. A key that does not register is usually a fault in the keyboard itself: a broken membrane trace, a worn contact pad or a bad connection at J8. The same keyboard matrix is drawn for the XE range as a whole in the reproduction of the 130XE service manual, and the guide applies equally to the Atari 800XE and to the PAL 65XEs sold in Poland (Atari 65XE (Poland)).

Symptoms

• One key, or a row or column of keys, does nothing.
• A key works only when pressed hard, or repeats.
• The whole keyboard is dead, or START, SELECT, OPTION or RESET does not work.
• The self test's keyboard test shows which keys are responding.

Safety

• Switch off and unplug the power before disconnecting the keyboard.
• Retrohax found the keyboard backplates of a batch of 65XEs stored in damp conditions badly rusted, and the LEDs corroded. Wear gloves and eye protection when removing rust.

Tools and parts

• A meter with a resistance range.
• Phillips #0 and #1 screwdrivers, a flat screwdriver, tweezers and latex gloves; Best's instructions recommend the gloves to keep sweat and fingerprints off the flat cable and the metal parts.
• For membrane traces: a conductive repair compound. Retrohax used a thermal-curing silver compound on 65XE membranes.
• For a dead contact pad: a replacement silicone dome. Retrohax fitted a pad cut down from a broken Amiga keyboard. Best Electronics sells replacement silicone dome contacts for XE keyboards (its "XE Touch" sets).
• For rust: a steel brush, sandpaper and a rust binder, as retrohax used.

Procedure

Open the case

1. Open the computer as described in Atari 65XE General Maintenance#Opening the machine, and disconnect the keyboard cable and the LED connector from the board.

Test the keyboard from the connector

1. Find the faulty key in the matrix below. Each key sits between one column pin and one row pin of J8.
2. Put the meter across those two pins at the keyboard cable's connector and press the key. A working key reads low; Sams gives about 55 Ω per key for the 130XE keyboard, which has the same matrix.
3. If every key in one column or one row fails, the fault is in that line: a cracked membrane trace or a bad contact in the connector, not the keys.
4. If the key does not read at all, open the keyboard to reach the membrane and the contacts.

65XE keyboard matrix: row pin (left) by column pin (top), all on J8 (Sobola sheet 7)

Row	19	4	8	9	10	11	17	16	20	21	22	23	24
13	7		8	9	0	<	>	Delete	Break
14	6		5	4	3	2	1	Esc
12	U		I	O	P	-	=	Return
15	Y		T	R	E	W	Q	Tab
7		J	K	L	;	+	*		Control
18		H	G	F	D	S	A	Caps
5	N	Space	M	,	.	/	Inverse
6		Help	B	V	C	X	Z		Shift
3										Start	Select	Option	Reset

The power LED, D1, is wired between J8 pins 2 and 3.

Open the keyboard

The metal bottom plate of an XE keyboard assembly, its screws circled (XE Game System keyboard)

Best Electronics' installation instructions for its replacement contacts were written for the XE Game System keyboard, whose four top function-key positions are the ones used on the 65XE, 130XE and 800XE keyboards. The assembly inside is opened as follows.

1. Lift the keyboard assembly out of the top case. In the reproduction of the 130XE manual it is held to the top cover by four screws.
2. Release the flexible flat cable from its black pinch connector evenly. Do not pull the membrane out at an angle, which can tear or crease it.
3. Remove all the small screws from the metal bottom plate and keep them together.
4. Lift off the metal plate, then lift out the double-layer membrane.
5. Turn the top housing over and the silicone contact cups fall out.

The bottom plate lifted off, with the double-layer membrane still lying in the top housing

Repair the membrane and contacts

1. Inspect the membrane traces for cracks and corrosion. Repair broken traces with conductive compound, as retrohax did with a thermal-curing silver compound, and cure it as the product requires. A membrane too badly damaged to repair has to be replaced; retrohax replaced several.
2. Replace contacts that no longer conduct. Best's replacement domes go in with the black contact dot facing up. Retrohax, lacking a spare, cut down a pad from an Amiga keyboard.
3. Replace corroded springs, and clean loose rust from the backplate before treating it.

Replacement silicone contacts going into the key positions of the top housing, black dot up

Reassemble the keyboard

1. Lay the membrane back on the inside of the top housing, locating it on its two plastic pins.
2. Refit the metal plate. Before tightening each screw, turn it gently anticlockwise until it clicks into its existing thread, then tighten it; otherwise the screw cuts a new thread each time and eventually stops holding.
3. Reconnect the flat cable and test each repaired key across its J8 pins again before refitting the keyboard.

If the keyboard tests good

The board side of the scan follows the 130XE's layout: POKEY's scan lines drive U24 and U25, which reach J8 through series resistors. On Sobola's 65XE drawing these are R146 to R161, marked 220 Ω, where Atari's 130XE schematic has R137 to R153 at 270 Ω. Work through the chip-level checks in Atari 130XE Keyboard Repair, which use the same POKEY, GTIA and CD4051 pins.

Testing

1. Reconnect the keyboard and LED, switch on with OPTION held and no cartridge or powered disk drive, and run the self test's keyboard test.
2. Press every key and check that each one shows on the screen.

Related pages

• Atari 65XE
• Atari 800XE
• Atari 65XE (Poland)
• Atari 65XE General Maintenance
• Atari 65XE Troubleshooting Guide
• Atari 130XE Keyboard Repair