Atari Stacy Troubleshooting Guide
This is a fault-finding guide for the Atari Stacy portable computer, called the LST in Atari's engineering drawings. The Stacy uses the 1040ST's chip set (GLUE, MMU, Shifter, DMA controller, 68901 MFP, YM2149, 1772) with a CMOS 68HC000, and adds an LCD controller, a real-time clock, an internal DC-DC converter, an electroluminescent backlight, a Trak-Ball and a battery compartment.[1]
Disconnect the DC adaptor and remove any cells from the battery compartment before opening the case. While the machine is on, the DC-DC converter produces 85 V AC for the backlight.[2]
Diagnostic equipment
[edit | edit source]- A multimeter for supply voltages and continuity, and an oscilloscope for clocks and ripple.
- An external ST monitor (SM124 or SC1224). The Stacy shows the same image on an external monitor as on its LCD.[3]
- An Atari ST diagnostic cartridge. At power-up TOS looks for a diagnostic cartridge in the cartridge port before it initialises the memory controller, and hands control to it if one is present.[4]
- A bench supply that can deliver 11–18 V at a few amps, to stand in for the adaptor.
Power supply diagnosis
[edit | edit source]The converter's specified input is 11–18 V DC.[2] The range is wide because the machine was designed to run from twelve C cells as well as from the adaptor.[5] An adaptor that holds a steady voltage anywhere in that range under load is within specification.
The converter's outputs, as labelled on Atari's drawing, are +5 V at 0.5–2.2 A for the logic, +5 V at up to 0.3 A and +12 V at up to 1 A on connector CN-B, small +5 V and +12 V outputs (up to 0.05 A each), −12 V and −20 V (up to 0.03 A each), and the 85 V, 590 Hz backlight output.[2] The drawing gives no tolerances. The main +5 V output is adjustable with trimmer VR1 on the converter.[2]
| Symptom | Possible cause | Action |
|---|---|---|
| Completely dead, no indicator lights | Adaptor; DC jack J14 or its joints; converter | Measure the adaptor output open circuit and under load; it should sit within 11–18 V. Check the DC jack for cracked solder joints. Then check the converter's +5 V output. |
| Starts, then drops out during disk access | Adaptor sagging; converter input capacitor C101 (1000 µF 25 V); converter fault | Watch the input and the +5 V output with a scope during a disk access. If the input holds and the +5 V collapses, the fault is on the converter. |
| Indicator lights on, nothing on the LCD or an external monitor | Logic fault; TOS EPROMs; sub board connection; +5 V low | Check +5 V at the main board. Reseat the socketed chips (TOS EPROMs on the sub board, GLUE, MMU, Shifter, DMA, Shadow) and the sub-board connectors. Fit the diagnostic cartridge. |
| Resets at random | DC jack; converter joints; low +5 V | Flex the DC jack while running. Inspect the converter's solder joints under magnification. Measure +5 V under load. |
| Crashes at random | Unstable +5 V; RAM; corrosion | Check the +5 V rail under load, then run the diagnostic cartridge's RAM tests. On the 4 MB sub board the 32 DRAMs (U5–U36) are soldered; only U1, U3 and U4 are socketed.[6] |
Display
[edit | edit source]The LCD is a 640 × 400 monochrome supertwist panel, driven as two halves split at line 200, with an electroluminescent backlight.[5][2] The LCD controller ("Shadow", U30) and its static RAM (U31) are on the main board.[1] The brightness, contrast and volume knobs are on the lid; the brightness knob switches the backlight off with a click at the end of its travel.[3]
| Symptom | Possible cause | Action |
|---|---|---|
| LCD blank, indicator lights on | Logic fault, or a display fault | Connect an external monitor. If it shows the desktop, the fault is in the LCD, its cable, the Shadow chip or the backlight. |
| Image readable but unlit | Brightness knob at its off click; screen saver; backlight | Turn the brightness knob clockwise off the switch. The Mouse Accelerator III screen saver can switch off the backlight alone after an idle period.[3] If neither applies, check for the converter's 85 V AC backlight output (with care) before suspecting the panel. |
| Whole screen goes dark after a few minutes | Screen saver set to blank the screen | Touch a key or move the Trak-Ball. Adjust the timer in Mouse Accelerator III.[3] |
| Image faint or washed out | Contrast knob; converter negative outputs | Adjust the contrast knob. Measure the converter's −12 V and −20 V outputs. |
| Image cuts in and out as the lid moves | Display cable at the hinge | Flex the lid slowly with the LCD running and watch for the fault; inspect the cable through the hinge. |
Clock and battery
[edit | edit source]The main board carries an RP5C15 real-time clock (U15) with a 32.768 kHz crystal (Y2), backed by a C103655-001 3 V 560 mAh lithium cell at location LB.[1] It is a primary cell, not a rechargeable pack.
| Symptom | Possible cause | Action |
|---|---|---|
| Date and time lost at every power-up | Clock cell exhausted | Measure the cell; replace it with a 3 V lithium cell of similar capacity. The machine runs without it. |
| Corrosion near the clock cell | Cell has vented | Remove it, neutralise and clean (lithium residue is acidic; use bicarbonate) and check the traces. See Battery Explosion, Capacitor or Corrosion Damage. |
| Corrosion in or near the battery compartment | Alkaline C cells left in the machine | Remove the cells, neutralise with vinegar, clean with isopropyl alcohol and repair damaged traces and contacts. |
Hard drive
[edit | edit source]Stacy 2 and Stacy 4 machines shipped with a 40 MB Conner hard disk.[7] The drive is SCSI, connected through Atari's ACSI-to-SCSI host adapter on the internal ACSI connector. The adapter supports a single drive at SCSI ID 0, with no termination fitted on the drive, does not generate parity and addresses only the first 1 GB.[8]
| Symptom | Possible cause | Action |
|---|---|---|
| Not found at boot | Drive failure; cable; no hard disk driver | Listen for spin-up. Reseat the cable. Boot a floppy with a hard disk driver. |
| Replacement drive or SD emulator not found | Wrong ID; termination on; parity required | Set the device to SCSI ID 0, turn its termination off and disable parity checking.[8] |
| Clicking or repeated seeking | Mechanical failure | Replace the drive, or fit an SD-card SCSI emulator configured as above. |
| Heads park on their own after a few minutes | Mouse Accelerator III Automatic Parking | Normal; the idle time is set in the utility.[3] |
See Hard Drive Maintenance and Repair.
Floppy drive
[edit | edit source]| Symptom | Possible cause | Action |
|---|---|---|
| Will not read any disk | Dirty heads; drive cable; 1772 controller (U18) | Clean the heads and try known-good disks. Reseat the drive cable. Try an external drive on the floppy port (J8).[1] |
| Reads but will not write | Write protect; drive | Check the disk's write-protect tab and try several disks before suspecting the drive. |
| Eject stiff or jammed | Mechanism | Inspect and clean the mechanism. See Floppy Drive Repair. |
Trak-Ball and keyboard
[edit | edit source]The keyboard is scanned by an HD6301V1 processor on the sub board (U1 on the 4 MB board), which reports to the CPU through one of the main board's ACIAs (U6, U7).[6][1] A slide switch on the right side panel selects the Trak-Ball or an external mouse on the Mouse/Joy port.[3]
| Symptom | Possible cause | Action |
|---|---|---|
| Pointer does not move with the Trak-Ball | Switch set to Mouse/Joy; dirty rollers; cable | Move the side-panel switch forward to the T-ball setting.[3] Clean the ball and rollers. Check the cable seating. |
| Pointer moves in one axis only | One roller or encoder dirty | Clean that roller and its encoder. |
| No key responds | Keyboard ribbon; HD6301V1; ACIA | Reseat the ribbon. The HD6301V1 is socketed on the 4 MB sub board.[6] |
| A row or column of keys dead | Shared trace or connector pin | Follow the shared line back to the connector. |
Bombs
[edit | edit source]If the machine boots far enough to show bombs, the number of bombs is the 68000 exception number. Atari's ST field service manual lists them:[4]
| Bombs | Exception |
|---|---|
| 2 | Bus error: GLUE asserted bus error or the CPU detected an error |
| 3 | Address error: word or long-word access at an odd address |
| 4 | Illegal instruction |
| 5 | Divide by zero |
| 6 | CHK instruction |
| 7 | TRAPV instruction |
| 8 | Privilege violation |
The manual also tells the technician to verify the disk and drive before repairing the computer, because errors loading a file from disk can crash the system.[4]
Related pages
[edit | edit source]- Atari Stacy
- Atari Stacy General Maintenance
- Atari Stacy Capacitor Replacement Guide
- Atari Stacy Schematics and Drawing Package
- Floppy Drive Repair
- Hard Drive Maintenance and Repair
- Battery Explosion, Capacitor or Corrosion Damage
References
[edit | edit source]- ↑ 1.0 1.1 1.2 1.3 1.4 Atari Corporation, STacy (LST) schematics and drawing package: bill of material CA200464-XXX Assy PCB LST Rev A, sheets 2–8 of 9 (PDF pp. 13–19). Sheet 5: 68HC000 U4, DMA U17, GLUE U9, Shifter U20, MMU U19, YM2149 U8, 6350 ACIAs U6/U7, 68901 U10, 1772 U18, crystals Y1 2.4576 MHz and Y2 32.768 kHz, oscillator OSC1 32.04245 MHz; sheet 6: TL7705A U1, RP5C15 U15, Shadow U30, SRAM U31, Trak-Ball/mouse switch S2; sheet 7: connectors; sheet 8: sockets (40-pin U17, U20; 68-pin PLCC U9, U19; 84-pin PLCC U30; 20-pin U25) and the clock battery at LB. Hosted as Atari Stacy Schematics and Drawing Package (PDF).
- ↑ 2.0 2.1 2.2 2.3 2.4 Atari Corporation, STacy (LST) schematics and drawing package: DC-DC Converter, drawing C101780-XXX Rev B, sheet 6 of 7, drawn 28 February 1990 (PDF pp. 46–47, the left and right halves of the sheet). Shows "DC input 11–18V", C101 1000 µF/25 V, the outputs (+5 V 0.5–2.2 A; +5 V 0–0.3 A and +12 V 0–1 A on CN-B; −12 V 0–0.03 A; −20 V 0–0.03 A; +5 V 0–0.05 A; +12 V 0–0.05 A; WARN1; WARN2) and "EL output 85V 590Hz" with the BRIGHT and EL OFF connections. Hosted as Atari Stacy Schematics and Drawing Package (PDF).
- ↑ 3.0 3.1 3.2 3.3 3.4 3.5 3.6 Atari Corporation, Stacy Addendum: Owner's Manual, C301421-001 Rev. A, 1989 (printed 1990). p. 7: brightness knob, backlight switch-off and Backlight/Screen screen saver; p. 8: Automatic Parking; p. 9: display, external monitor, Trak-Ball/mouse switch; p. 10: lid controls and indicator lights. Hosted as File:Atari Stacy Owner's Manual Addendum C301421-001.pdf.
- ↑ 4.0 4.1 4.2 Atari Corporation, 520ST/1040ST Computer Field Service Manual, C026118-002 Rev B (3.6), January 1987: section 2.14 power-up sequence and section 2.15 system errors, pp. 2.15–2.16 (PDF pp. 25–26); section 3, testing with the diagnostic cartridge. Hosted as Atari 520ST and 1040ST Computer Field Service Manual (PDF).
- ↑ 5.0 5.1 Atari Computer, Stacy Product Backgrounder, press release, Las Vegas, November 1989, pp. 1 and 8 (power: "Internal by 12 standard 'C' batteries; DC input jack for use with external DC source"; display: supertwist backlit LCD, 640 × 400, split horizontally at line 200). Scan at https://archive.org/details/19891100AtariComputersStacyAFullFunctionLaptop (retrieved 2026-10-01).
- ↑ 6.0 6.1 6.2 Atari Corporation, STacy (LST) schematics and drawing package: bill of material CA200528-XXX Assy Sub PCB LST-4 Rev B, sheets 2–5 of 6 (PDF pp. 6–9): C7 1000 µF 16 V; DRAM C103641 1M × 1 ZIP at U5–U36; HD6301V1 U1; TOS 1.4 EPROMs U3 (high) and U4 (low); sockets only at U1 (40-pin), U3 and U4 (32-pin); connectors J1 (24-pin FFC), J2 (60-pin), J3 (50-pin). Hosted as Atari Stacy Schematics and Drawing Package (PDF).
- ↑ Stephen Mortimer, "News, Notes & Quotes", START vol. 4 no. 9, April 1990: "Both systems come with the respective amount of memory and a 40MB Conner hard disk drive." https://www.atarimagazines.com/startv4n9/newsnotesquotes.html
- ↑ 8.0 8.1 Joska ([email protected]), Some notes about the Stacy/Mega STE internal SCSI host adapter, 2014 (community notes), p. 1. Copy at https://archive.org/details/manualzz-id-770197 (retrieved 2026-10-01).