Atari 800XL Troubleshooting Guide
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Fault-finding on the Atari 800XL follows Atari's 800XL Computer Field Service Manual (FD100740 Rev. 01, February 1984): the built-in self test, the symptom checklist in section 3, and the schematic and parts list in section 5.[1] Every chip on the board has its own U number; the ones that matter most are the 6502C CPU (U8), ANTIC (U7), GTIA (U17), POKEY (U22), the PIA (U23), the MMU (U3), the BASIC and operating system ROMs (U4 and U5) and the DRAMs (U9–U16).[1]
Before you start
[edit | edit source]- The 800XL takes +5 V DC through a 7-pin DIN socket (J7). Atari's supply delivers +5 V ±2 % (4.90–5.10 V) at up to 1.2 A. Measure it at the plug before connecting it: the board has no regulator, rectifier or fuse, so whatever the supply delivers reaches the chips.[1]
- The board filters the switched +5 V into three rails, +5A, +5B and +5C.[1]
- Remove any cartridge and unplug all SIO devices. With no cartridge and no powered disk drive the 800XL starts in Atari BASIC; holding OPTION at power-on disables BASIC and, with no cartridge or disk, starts the self test.[1][2]
- If the machine starts with OPTION held but not without it, the built-in BASIC is the first suspect; Atari's checklist puts a failed ROM test on U2–U5.[1]
Self test
[edit | edit source]Hold OPTION while switching on, with no cartridge fitted. The menu offers Memory, Audio Visual, Keyboard and All Tests; SELECT moves the indicator and START runs the test. SYSTEM RESET leaves the self test for BASIC, and HELP returns from a test to the menu.[1]
- Memory tests the ROM, RAM and ANTIC. Two long bars represent the 16 KB operating system ROM and 48 blocks represent 1 KB of RAM each; the remaining 16 KB of RAM is not tested. A segment turns white while being tested, light green if good and red if bad, and a red segment is not retested.[1]
- Audio Visual tests ANTIC and POKEY: six tones play on each of the four channels in turn with the note shown on a staff. A note without a sound, or a sound without a note, is a fault.[1]
- Keyboard tests POKEY, ANTIC and the ROM: each key pressed shows in inverse video with a tone. CONTROL and SHIFT change only when pressed with another key.[1]
Atari warns not to leave a self-test screen up for more than about seven minutes, because the self test has no attract mode and the screen can burn.[1] Atari's field test was the SuperSALT diagnostic cartridge (FD100335) with the SuperSALT test assembly (FA100332); its procedures are in a separate SuperSALT Technical User's Manual (FD100770).[1]
Symptom checklist
[edit | edit source]Atari lists the possible causes for each symptom in order of likelihood.[1]
| Symptom | Possible causes | Remedy |
|---|---|---|
| Snowy screen | TV switch box, on/off switch, channel select switch, RF modulator | Adjust or replace |
| Defective power supply, damaged RF cable | Replace | |
| Defective (open) components on the +5C line | Isolate and replace | |
| Defective (shorted) components on the +5A, +5B or +5C lines | Isolate and replace | |
| Defective (shorted) LSIs or ICs | Isolate and repair | |
| Black or grey screen | Y1, Q8, Q9, C109 | Troubleshoot the clock circuit |
| U2, U7–U20, U22, U23, U26–U30 | Isolate and replace the defective IC | |
| Red or brown screen | U2–U5, U18, U19, U28, U30 | Isolate and replace the defective IC |
| Blue screen | U2 | Replace |
| Yellow screen | U28 | Replace |
| No colour or bad colour | RF modulator or R38 | Adjust or replace |
| U17, U20, Q1, Q3, CR2, CR3 | Troubleshoot the colour and video circuit | |
| Y1 | Check for 3.579545 MHz; replace if faulty | |
| No power light (L1) | Power LED, power supply, cables | Repair or replace |
| No grey bars or a missing bar | U17, U20 | Repair or replace |
| Upside-down characters on the player field | U7 | Replace |
| Some keyboard keys fail | U22, keyboard, U24, U25, cable | Repair or replace |
| All keyboard keys fail | U22, U24, U25 | Repair or replace |
| Tones missing in the tone test | U22, U1, 4.5 MHz audio carrier, TV volume | Repair; adjust the 4.5 MHz carrier on the RF modulator |
| Console switches do not work | U17, keyboard, cable | Repair or replace |
| ROM test failed | U2–U5 | Repair or replace |
| RAM test failed | U2, U3, U9–U16, U18, U19, U26–U30 | Check that ANTIC is Rev. E; repair or replace |
| Video or ANTIC stress fail | U7 | Repair or replace |
| CPU test fail | Y1, Q8, Q9, U8 | Check the 3.58 MHz oscillator; repair or replace |
| Two-way clock fail (SuperSALT) | J1, U22 | Repair or replace |
| External audio (SuperSALT) | J1, U1 | Repair or replace |
| GTIA fail | U17 | Replace |
| Port test: voltage at P1, P2 | L25, J5, J6 | Inspect J5 and J6 for damaged pins |
| Port test: voltage at MC | Q7, L11, U2 | Repair or replace |
| Port test: PIA ports | U23, C26–C29, C82–C92, L19–L22 | Repair or replace |
| Port test: SIO port | U22, U23, C75–C78 | Repair or replace |
| Port test: trigger lines | U17, L23, L30, C96, C97 | Repair or replace |
| Port test: POT lines | U22, L15–L18, C71–C74, C63–C66 | Repair or replace |
| Port test: timers | U22 | Replace |
R38 is the 500 kΩ colour trimmer. Y1 is the 3.579545 MHz crystal (C061090) on domestic boards; the schematic's notes give 3.546894 MHz (C015510) for the U.K. board. The clock oscillator uses the 2N3906 transistors Q8 and Q9.[1]
Supply pins
[edit | edit source]| Device | Location | VCC | Ground |
|---|---|---|---|
| 6502C | U8 | 8 | 1 and 21 |
| ANTIC | U7 | 21 | 1 |
| GTIA | U17 | 27 | 3 |
| POKEY | U22 | 17 | 1 |
| PIA | U23 | 20 | 1 |
On the 6502C, pin 40 is RESET, pin 37 the φ0 clock input and pin 39 φ2 out.[1][3] The CPU runs at 1.79 MHz on NTSC machines and 1.77 MHz on PAL machines.[2]
Connectors
[edit | edit source]- SIO (J1): pin 10 is +5 V/ready and pin 12 is not connected on the XL machines.[2] POKEY handles the serial data and clocks; Atari's SIO port test names U22, U23 and C75–C78.[1]
- Controller jacks J5 and J6, 9-pin: pin 7 is +5 V and pin 8 ground. A missing voltage there points at L25 and the jacks themselves.[1][2]
- Keyboard: a 24-way ribbon to the header J8, plus a ground strap that must be refitted when the top cover goes back.[1]
- Monitor socket J2: see the output levels on the Atari 800XL page.
Disassembly
[edit | edit source]Six screws hold the bottom cover. Tip the top cover up from the left, disconnect the keyboard ground strap and the keyboard cable, then remove the four screws holding the board and lift its front while pushing out the right side of the bottom housing until the controller ports clear. Do not swap top or bottom housings between units.[1]
Related pages
[edit | edit source]- Atari 800XL
- Atari 800XL General Maintenance
- Atari 800XL Capacitor Replacement Guide
- Atari 600XL Troubleshooting Guide
- Atari 130XE Troubleshooting Guide
References
[edit | edit source]- ↑ 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 1.11 1.12 1.13 1.14 1.15 1.16 1.17 1.18 Atari, Inc., 800XL Computer Field Service Manual, FD100740 Rev. 01, February 1984. Section 1 (theory of operation and pin assignments, pp. 1-1 to 1-15), Section 2 (testing, pp. 2-1 to 2-3), Section 3 (symptom checklist, pp. 3-1 to 3-3), Section 4 (disassembly, p. 4-1), Section 5 (schematic, silkscreen and parts list). Hosted here as File:Atari 800XL Computer Field Service Manual FD100740 Rev 01.pdf.
- ↑ 2.0 2.1 2.2 2.3 Michael D. Current (ed.), Atari 8-Bit Computers: Frequently Asked Questions, comp.sys.atari.8bit FAQ, last modified 29 November 2009, section 1.6 "What is the Atari 800XL?" (boot options, board versions) and section 1.16 (port pinouts). faqs.org. Community reference.
- ↑ Atari, Inc., 1200XL Field Service Manual, FD100217, figures 1-4 to 1-8 (6502C, ANTIC, GTIA, POKEY and PIA pin assignments), the same devices as the 800XL. Hosted here as Atari 1200XL Field Service Manual.