Sams Computerfacts Atari 800XL
Sams Computerfacts CC11 is the service data that Howard W. Sams & Co. of Indianapolis published for the Atari 800XL in July 1985 (cover code 85CC14952, dated 7-85). It covers the main board: schematics marked with voltages and waveforms, photographs of the board with component locations, a troubleshooting guide, logic charts, a parts list with replacement-part cross-references, adjustments and disassembly, and a Preliminary Service Checks insert. It is not an Atari document; Atari's own manual is the Atari 800XL Computer Field Service Manual.
The hosted PDF is a 33-page scan; several sheets carry two printed pages side by side, so PDF page numbers do not follow Sams' page numbers.
Contents
[edit | edit source]The cover index, with Sams' page numbers:
| Section | Pages |
|---|---|
| Schematics, main | 2, 27, 28, 29 |
| Schematic, power supply (the board's power input) | 3 |
| IC pinouts and terminal guides | 4, 25 |
| Test equipment | 5 |
| Troubleshooting | 5–8 |
| Photos, main board | 9, 10, 19, 20 |
| GridTrace location guide | 11 |
| Safety precautions | 12 |
| Schematic notes | 13 |
| Parts list | 14–17 |
| Line definitions | 18 |
| Block diagram | 21 |
| Logic chart | 22, 23 |
| Miscellaneous adjustments | 24 |
| Disassembly instructions, general operating instructions | 26 |
What the troubleshooting guide gives
[edit | edit source]The guide works stage by stage and names the test pin and the parts to check at each step.
- Self test: hold Option while switching on, or type BYE in BASIC. The memory test shows two bars for the operating system ROM (U5) and 48 squares, one per kilobyte of RAM in U9–U16.
- Power: with the power pack unplugged, its plug P7 should give 5.0 V from pin 3 to pin 1. Before fitting a new pack, check for a short from pin 3 to pin 1 of jack J7 with the power switch S1 on. With the pack connected, 5.0 V should appear on the positive end of C2.
- Processor: the reset output at pin 8 of U19 goes low briefly and then high at switch-on or when Reset is pressed (if not, check C49, CR1, R39, R40 and U19); a 1.78977 MHz clock appears at pin 11 of U18.
- Clock and dividers: 3.579545 MHz at the collector of the oscillator transistor Q8, then GTIA (U17) pin 29, 1.78977 MHz at ANTIC (U7) pin 34, U18 pin 6, CPU (U8) pins 3 and 39, U18 pin 11, U19 pin 2 and the delay line U29 pins 4, 6, 8, 10 and 12.
- Video, colour and sync: RF modulator pin 1, the emitter and base of the video amplifier Q3 (L6, R54), U20 pin 5 (R49); the colour control R38 should swing GTIA pin 17 from 0 to 8.5 V, with 3.579545 MHz at GTIA pin 28; colour from GTIA pin 21 through Q2, Q4 and Q5 (C54, C55, R67, R68); sync from GTIA pin 25 through U20, CR4 and R51.
- Sound: a one-line BASIC test program, POKEY pin 37, the audio amplifier U1 pin 1 and the modulator's sound coil L202; key click from GTIA pin 15 (C23, R5); the monitor jack J2 (R8, R10); audio inputs at J9 pin 49 (C22) and J1 pin 11 (C19, C110).
- Keyboard: J8 and the ribbon, POKEY pins 18–23, multiplexer U24 pin 3, U24 and U25; START, SELECT and OPTION at GTIA pins 12, 13 and 14 (R134–R136); SHIFT, CONTROL and BREAK at POKEY pin 16 and U25 pin 5 (R96, R137); a chart of which keys connect to each J8 pin, and a reading of about 55 Ω across each key.
- Cassette: POKEY pins 26, 27, 28 and 24 and J1 pins 1, 2, 3 and 5; the motor control at PIA (U23) pin 39 and Q7, switched with POKE 54018,52 and 54018,60.
- Paddles and joysticks: BASIC test programs and charts of the POKEY, PIA and GTIA pins for each port.
Miscellaneous adjustments (p. 24): adjust the colour control R38 for a blue screen; the RF modulator's channel coil L201 and sound coil L202.
Disassembly (p. 26): six screws in the cabinet bottom; four screws hold the board; the shield is held together by ten screws.
What it does not contain
[edit | edit source]- The external power pack is treated as a replaceable unit; there is no schematic of the pack itself. The "power supply" schematic on page 3 is the board's power input.
- The parts list gives replacement types (General Electric, NTE, ECG, RCA, Workman and Zenith) for the semiconductors. Its electrolytic capacitor table lists only C19, C20 and C22 (4.7 µF 35 V non-polarised); other values are on the schematic only.
- Its parts list has no FREDDIE chip: it describes the original board, with U.K. parts marked, not the later PAL "800XLF" board.
Pages that cite this document
[edit | edit source]- Atari 800XL Black Screen Repair
- Atari 800XL Controller Port Repair
- Atari 800XL Keyboard Repair
- Atari 800XL RAM Replacement
- Atari 800XL SIO Port Repair
- Atari 800XL Sound Repair
- Atari 800XL Video Output Repair