Atari STE General Maintenance

This guide covers general maintenance procedures for the Atari 520STE and Atari 1040STE computers. Released in late 1989, the STE (ST Enhanced) models feature an updated motherboard design with several improvements over the earlier ST/STF/STFM range, including SIMM-based RAM, a hardware blitter, DMA stereo sound, and an enhanced colour palette. Both the 520STE and 1040STE use the same motherboard — the only difference is the amount of RAM installed (512 KB vs 1 MB via SIMMs).

For the earlier Atari ST/STF/STFM range (520ST, 1040ST), see Atari ST General Maintenance.

Key Differences from the ST/STF/STFM

The STE motherboard differs from the earlier ST family in several ways relevant to maintenance:

• RAM is on SIMMs (30-pin, 256 KB or 1 MB modules) rather than soldered DRAMs. This makes RAM testing and replacement much simpler.
• The GLUE and MMU are combined into a single surface-mounted IC: the GST MCU (C300720 / C300589). This is a 144-pin QFP package soldered directly to the board — it cannot be socketed or easily replaced.
• The Shifter is replaced by the GST Shifter, which also handles DMA sound. On some board revisions the GST Shifter is also surface-mounted.
• The blitter (BLiTTER chip) is present as standard.
• TOS ROMs are typically TOS 1.62 (2× 128 KB) or TOS 2.06 (2× 128 KB). TOS 2.06 is recommended.
• Two board revisions exist: CA401177 (earlier, sometimes with SMD 68000 CPU) and CA4003290 (later, more common).

Safety Precautions

WARNING: The STE contains an internal switched-mode power supply with mains-voltage components. The same safety precautions apply as for the 1040ST — disconnect mains, wait 5 minutes, do not touch PSU internals. See ST General Maintenance — Safety Precautions for full details.

Opening the Case

The 520STE and 1040STE share the same case design:

1. Unplug the mains cable and all peripherals.
2. Turn the machine upside down on a soft surface.
3. Remove the screws from the bottom of the case (typically 5 Phillips-head screws).
4. Separate the top case from the bottom, watching for the keyboard ribbon cable.
5. The PSU and floppy drive are in the top half. Disconnect the PSU power header and floppy ribbon cable from the motherboard.

Cleaning

General cleaning procedures are the same as for the ST family. See ST General Maintenance — Cleaning for external, internal, and floppy drive cleaning instructions.

Additional STE-specific notes:

• SIMM sockets: Clean the SIMM socket contacts with IPA and a soft brush if RAM errors are suspected. Oxidation on SIMM contacts is a common cause of boot failures.
• Enhanced joystick ports: The STE has two additional 15-pin enhanced joystick ports on the left side of the case. Clean these with IPA and compressed air.

SIMM Memory Maintenance

The STE uses 30-pin SIMM modules for RAM. Supported configurations:

Configuration	SIMM Slots	Total RAM	Notes
520STE default	2× 256 KB	512 KB	Factory configuration
1040STE default	4× 256 KB or 2× 512 KB	1 MB	Factory configuration
2 MB upgrade	2× 1 MB	2 MB	Two SIMM slots populated
4 MB maximum	4× 1 MB	4 MB	All four SIMM slots populated

Important: The STE does not recognise a 2.5 MB configuration (2× 1 MB + 2× 256 KB mixed). All SIMMs must be the same size within each bank pair. A mismatched configuration may cause the machine to detect only 2 MB or fail to boot.

Maintenance procedure:

1. Power off and unplug the machine.
2. Release the SIMM retaining clips and gently remove each module.
3. Clean the SIMM edge contacts with a pencil eraser (gently) followed by IPA.
4. Clean the socket contacts with IPA and compressed air.
5. Reinsert SIMMs firmly until the retaining clips snap into place.
6. If troubleshooting RAM faults, try swapping SIMM positions or substituting with known-good modules.

Socketed IC Maintenance

Fewer ICs are socketed on the STE compared to the earlier ST range. The GST MCU and GST Shifter are surface-mounted on most boards and cannot be removed. However, the following are typically socketed on both the 520STE and 1040STE:

IC	Function	Package	Notes
MC68000	CPU	DIP-64 (CA4003290) or QFP-68 SMD (some CA401177)	DIP versions can be reseated; SMD versions cannot.
TOS ROMs (2 chips)	Operating system	DIP-32	TOS 1.62 or 2.06. Socketed for upgrades.
WD1772	Floppy controller	DIP-28	Socketed on most boards.
YM2149F	Sound PSG / PIO	DIP-40	Socketed. Controls drive select, printer port, and legacy sound.
MC68901 (MFP)	Timers/interrupts/UART	DIP-48	Socketed.
MC6850 (×2)	ACIAs (Keyboard/MIDI)	DIP-24	Socketed.
BLiTTER	Graphics blitter	PLCC-68	Socketed in PLCC socket.

Reseat all socketed ICs as part of routine maintenance, as per the procedures described in ST General Maintenance — Socketed IC Maintenance.

Solder Joint Inspection

Key areas specific to the STE:

• GST MCU (U400): This 144-pin QFP surface-mount chip handles GLUE, MMU, and additional STE functions. Inspect the solder joints under magnification. Cracked or cold joints on this chip are difficult to repair without SMD rework equipment. If suspected, a skilled technician can reflow the joints with a hot-air station.
• GST Shifter: Also surface-mounted on some boards. Same inspection procedure as GST MCU.
• SIMM sockets: Check solder joints on the SIMM socket pins — these can crack from the mechanical stress of inserting and removing SIMMs.
• Power header, DB-25, DB-19, DIN connectors: Same inspection as ST family — see ST General Maintenance — Solder Joint Inspection.

STE-Specific Reset Issue

A well-known issue on the STE is failure to reset properly on power-on. Symptoms include the machine sometimes booting and sometimes showing a white screen, requiring multiple power cycles. This is caused by the electrolytic capacitor in the reset circuit (part of the RC network that holds the 68000 in reset during power-up) losing capacitance with age.

The fix is to replace the reset circuit capacitor. The voltage across this cap is typically 10V–63V depending on board revision. Replacing it with a fresh, high-quality capacitor (check value on your specific board — typically 22 µF or 47 µF) resolves the intermittent reset problem.

This fix also applies to STFM, Falcon, and Mega ST machines with similar reset circuits.

Keyboard and Port Maintenance

Same procedures as the ST family — see ST General Maintenance. The STE keyboard is the same design and uses the same IKBD controller.

The STE adds two enhanced joystick ports (active DE-15 connectors on the left side of the case, compatible with Jaguar controllers). These should be cleaned with IPA and checked for bent pins.

Preventive Maintenance Schedule

Interval	Task	Applies To
Every use	Ensure adequate ventilation.	Both 520STE and 1040STE
Annually	Clean floppy drive heads. Blow out dust.	Both models
Every 5 years	Reseat all socketed ICs and SIMMs. Inspect solder joints.	Both models
Once (if not already done)	Recap the PSU.	Both models
Once (if not already done)	Recap the motherboard (see Atari STE Capacitor Replacement Guide).	Both models
Once (if not already done)	Replace the reset circuit capacitor if intermittent boot is observed.	Both models

Related Pages

• Atari 1040STE
• Atari STE Troubleshooting Guide
• Atari STE Capacitor Replacement Guide
• Atari ST General Maintenance