Atari 130XE Keyboard Repair

The Atari 130XE has a 62-key full-stroke keyboard joined to the main board by a 24-conductor foil cable at the connector J8.^[1] POKEY (U22) scans it: its outputs K0 to K5 address the two CD4051 multiplexers U24 and U25, which connect the keyboard lines one at a time through 270 Ω resistors (R137 to R153) to POKEY's return inputs KR1 (pin 25) and KR2 (pin 16). SHIFT, CONTROL and BREAK return on KR2, and the START, SELECT and OPTION keys go to the GTIA (U17) through R134 to R136.^[2] Sams' service data gives a check for each part of the scan, and a chart of which keys sit on each pin of J8.^[3]

Symptoms

The whole keyboard is dead.^[3]
One key, or a group of keys, does not work, or one key is erratic.^[3]
START, SELECT or OPTION does not work.^[3]
SHIFT, CONTROL or BREAK does not work.^[3]
Wrong characters appear when a key is pressed.^[3]
No click when a key is pressed (see also Atari 130XE Sound Repair).^[3]

Safety

The keyboard is joined to the board by a foil cable; disconnect it before lifting the top clear of the base.^[3]^[1]
Switch off before unplugging the keyboard or removing chips.

Tools and parts

An oscilloscope, a logic probe and a meter.^[3]
Replacement parts as found: CD4051B multiplexers for U24 and U25 (Atari C014336), 270 Ω resistors for R137 to R153, 220 Ω for R134 to R136, 47 kΩ for R96.^[2] Atari's part number for the keyboard assembly is C070015 and for the 24-pin keyboard connector J8 C061793.^[2]

Procedure

Open the machine

Remove the four screws from the bottom of the case. Lift the top up and disconnect the keyboard cable; the top can then be removed.^[3]
For board checks, remove the seven screws holding the board, lift out the board and shield, and twist the seven tabs to separate the shield halves.^[3] Reconnect the keyboard and power.
To remove the keyboard itself, disconnect the keyboard connector and the power LED connector, noting how the LED connector fits, and remove the four screws that hold the keyboard to the top cover.^[1]

Whole keyboard dead

Check J8 for good connections and the foil cable for damage.^[3]
If the connector and cable are good, check for waveforms at POKEY (U22) pins 18 to 23, the scan outputs. If they are missing, suspect U22.^[3]
If they are present, check for a waveform at pin 3 of the multiplexer U24 while pressing any key other than SHIFT, CONTROL, BREAK or the function keys. If it is missing, check U24 and U25. If it is present, check the GTIA (U17) and U22.^[3]

START, SELECT or OPTION dead

Check the logic levels at GTIA (U17) pins 12, 13 and 14. Pin 12 should go low when START is pressed, pin 13 when SELECT is pressed, and pin 14 when OPTION is pressed.^[3]
If the levels are correct, suspect U17. If they are not, check J8, the cable and the resistors R134, R135 and R136.^[3] On Atari's schematic these keys reach J8 at pins 21, 22 and 23.^[2]

SHIFT, CONTROL or BREAK dead

Check for a waveform at POKEY (U22) pin 16 while pressing SHIFT, CONTROL or BREAK. If it is present, suspect U22.^[3]
If it is missing, check for the same waveform at U25 pin 5 while pressing SHIFT, at U25 pin 4 while pressing CONTROL, and at U25 pin 14 while pressing BREAK. If it is missing at the pin for that key, suspect U25.^[3]
If it is present at U25, check R96 and R137 and the connections at J8.^[3] On Atari's schematic R137 feeds J8 pin 20, and R96 (47 kΩ) pulls the KR2 line up to +5A.^[2]

One key or a group of keys dead

An erratic single key: clean the key.^[3]
To open the keyboard assembly and repair its membrane or contacts, follow Atari 65XE Keyboard Repair, which covers the same XE keyboard matrix.
Find the J8 pins for the dead keys in Sams' chart. Check each key for continuity; Sams gives about 55 Ω per key.^[3]
If the keys measure correctly, switch on and use the scope to look for pulses at those J8 pins while pressing the dead keys. A logic probe may show pulses even when no key is pressed, so use the scope.^[3]
If the pulses are missing, check the resistors between J8 and U24 or U25, and check U24 and U25.^[3]

**J8 pins, series resistors and multiplexers (Atari schematic C070065)**
Multiplexer	J8 pins and resistors
U24	17 (R146), 11 (R147), 8 (R148), 16 (R149), 19 (R150), 10 (R151), 4 (R152), 9 (R153)
U25	18 (R145), 13 (R144), 15 (R143), 5 (R142), 14 (R141), 6 (R140), 12 (R139), 7 (R138)
KR2 line (SHIFT, CONTROL, BREAK)	20 (R137)

^[2]

Wrong characters

Check ANTIC (U7), GTIA (U17) and POKEY (U22).^[3]

Refit

Refit the keyboard to the top cover with its four screws and reconnect the keyboard and LED connectors without twisting the LED cable.^[1]
Refit the shield, the board and the top, reconnecting the keyboard cable before the top goes down.^[1]

Testing

Run the self test's keyboard test: hold OPTION while switching on, select KEYBOARD and press START. Each key pressed should turn inverse on the screen and sound a tone. CONTROL and SHIFT only show when pressed with another key, and RESET, HELP and BREAK are not tested.^[3]

Related pages

References

↑ ^1.0 ^1.1 ^1.2 ^1.3 ^1.4 130XE Personal Computer Field Service Manual, reproduction by JER/Eightbitter, November 2016: section 1 (62-key keyboard, 24-conductor foil cable, power LED), section 2 (figure 2-15, keyboard matrix by J8 pin), section 4 (console disassembly and assembly, keyboard removal and replacement). Not an Atari publication. Hosted here as Atari 130XE Field Service Manual.
↑ ^2.0 ^2.1 ^2.2 ^2.3 ^2.4 ^2.5 Atari Corp., 130XE Reference Manual (cover dated March 1990): parts list of 25 June 1985 (U24 and U25 CD4051B C014336; R137-153 270 Ω; R132-136 220 Ω; R96 47 kΩ; keyboard assembly C070015; J8 C061793); schematic diagram C070065 Rev. B (POKEY keyboard lines, U24, U25, R137-R153, R96, J8 pins 20 to 23). Hosted here as Atari 130XE Parts List and Production Test Instructions.
↑ ^3.00 ^3.01 ^3.02 ^3.03 ^3.04 ^3.05 ^3.06 ^3.07 ^3.08 ^3.09 ^3.10 ^3.11 ^3.12 ^3.13 ^3.14 ^3.15 ^3.16 ^3.17 ^3.18 ^3.19 ^3.20 ^3.21 ^3.22 ^3.23 ^3.24 Howard W. Sams & Co., Sams Computerfacts CC16, Atari Model 130XE: "Self-Test" (PDF page 9); troubleshooting, "Keyboard", with the chart of J8 pins and keys (PDF page 10; its text calls the connector J9 but the chart and the rest of the document use J8); preliminary service checks and disassembly instructions (PDF pages 19 to 21). Hosted here as Sams Computerfacts Atari 130XE.

[fsm-1] 1.0 ^1.1 ^1.2 ^1.3 ^1.4 130XE Personal Computer Field Service Manual, reproduction by JER/Eightbitter, November 2016: section 1 (62-key keyboard, 24-conductor foil cable, power LED), section 2 (figure 2-15, keyboard matrix by J8 pin), section 4 (console disassembly and assembly, keyboard removal and replacement). Not an Atari publication. Hosted here as Atari 130XE Field Service Manual.

[parts-2] 2.0 ^2.1 ^2.2 ^2.3 ^2.4 ^2.5 Atari Corp., 130XE Reference Manual (cover dated March 1990): parts list of 25 June 1985 (U24 and U25 CD4051B C014336; R137-153 270 Ω; R132-136 220 Ω; R96 47 kΩ; keyboard assembly C070015; J8 C061793); schematic diagram C070065 Rev. B (POKEY keyboard lines, U24, U25, R137-R153, R96, J8 pins 20 to 23). Hosted here as Atari 130XE Parts List and Production Test Instructions.

[sams-3] 3.00 ^3.01 ^3.02 ^3.03 ^3.04 ^3.05 ^3.06 ^3.07 ^3.08 ^3.09 ^3.10 ^3.11 ^3.12 ^3.13 ^3.14 ^3.15 ^3.16 ^3.17 ^3.18 ^3.19 ^3.20 ^3.21 ^3.22 ^3.23 ^3.24 Howard W. Sams & Co., Sams Computerfacts CC16, Atari Model 130XE: "Self-Test" (PDF page 9); troubleshooting, "Keyboard", with the chart of J8 pins and keys (PDF page 10; its text calls the connector J9 but the chart and the rest of the document use J8); preliminary service checks and disassembly instructions (PDF pages 19 to 21). Hosted here as Sams Computerfacts Atari 130XE.

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