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Atari Mega STE General Maintenance

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Atari Mega STE with monitor, keyboard and mouse

The Atari Mega STE has an internal switching power supply, a lithium clock battery on a lead, an internal floppy drive mounted in the top cover, an optional internal SCSI hard disk, SIMM memory and a VMEbus slot. These are the parts that need attention on a machine of this age.

Safety

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Warning: the power supply's primary side runs at rectified mains voltage and its reservoir capacitor holds a dangerous charge after the machine is unplugged. Unplug the machine before removing the cover, and measure the primary capacitors before working on the supply. See Atari Mega STE Capacitor Replacement Guide.

Atari's installation manuals for the machine ask for work inside it to be done in a static-free environment.[1]

Opening the case

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Switch off and disconnect every cable, including the keyboard and mains lead. Atari's procedures start by removing the hard disk (if one is fitted) and the accessory cover over it, then the top cover.[1][2] The SIMMs can be reached with only the hard disk cover removed.[3] The floppy drive is mounted in the top cover, so its cables have to be unplugged before the cover comes fully away.[2] When lifting the supply out, take care not to knock components on the main board beside it.[4]

Cleaning

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Clean the outside with a soft, slightly damp, lint-free cloth with the machine switched off, without cleansers, abrasives or solvents.[5] Inside, remove dust from the board and supply with a soft brush and low-pressure air, and check the ribbon cables to the floppy drive and hard disk for damage.

Clock battery

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The Ricoh RP5C15 clock (U402) is powered from the battery connector J401 through a diode, D401, which stops the battery being charged.[6] The original battery is a Tadiran TL-5242/W: a non-rechargeable 3.6 V lithium cell in a sleeve, on a lead with a plug, fixed inside the case with Velcro. A replacement 3.6 V lithium cell can be wired to the original plug; keep the plug housing so the polarity cannot be reversed.[7] Set the date and time after the change. A clock that stops when the machine is switched off has a flat cell. See Battery Refurbishment.

Power supply

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The supply feeds the board through the 12-way connector J201:[6]

J201 power connector
Pin Signal
1 Power Good
2, 10, 11, 12 +5 V
3 +12 V
4 −12 V
5, 6, 7, 8 Ground
9 −5 V

Check all four rails. The −5 V rail feeds the DMA sound converters, and −12 V the serial port drivers, so a machine with one of them missing may still start.[6] Atari's Mega STE documents give no rail tolerances. The same Phihong PSM-5341 supply is used in the TT030, for which Atari rates it at +5 V 7 A, +12 V 2 A, −5 V 0.4 A and −12 V 0.3 A.[8][9] Recapping the supply is covered in Atari Mega STE Capacitor Replacement Guide.

J291 is a three-pin header for a second fan, fed from +12 V.[6]

Fuses on the main board

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Two 0.5 A fuses on the main board protect external connectors: F21 in the +5 V feed to the cartridge port and F31 in the supply to the keyboard socket.[6] A dead keyboard or cartridge port on an otherwise working machine is worth checking against these before anything else.

Floppy drive

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Early machines have a 720 KB drive and later ones a 1.44 MB drive; Atari's upgrade kit converts the first to the second.[3][2] Clean the heads with isopropyl alcohol on a lint-free swab or a cleaning disk.[10] Replacement drives without their own pull-up resistors, such as the Sony MPF920, need pull-ups added to the floppy controller's outputs; exxos lists this fix for the STE and Mega ST.[10] See also Floppy Drive Repair.

Hard disk

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The optional internal hard disk is a SCSI drive on a host adapter that plugs into the main board.[3] The owner's manual's appendix C covers Atari's hard disk utilities, including installing the driver and partitioning.[11] Back up an original drive before it fails; see Hard Drive Maintenance and Repair.

Memory

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Use SIMMs in matched pairs; with one pair, fit U701 and U703.[3][12] exxos advises against parity SIMMs in STE machines unless the parity chip is removed, because they have proved unstable, particularly with a failing supply.[10]

Keyboard, mouse and VME card

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The keyboard plugs into a six-way modular socket;[3] replace a damaged coiled cord with a six-wire cord wired pin 1 to pin 1.[13] The mouse and joystick ports are on the sides of the keyboard. A mouse that moves slowly or erratically may need cleaning.[5] A VME card fits from the back of the case after removing the slot cover; reseat it if the machine becomes unreliable with the card fitted.[3]

Maintenance checklist

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  1. Check the fans turn.
  2. Replace the clock battery if it is flat, and check for corrosion around it.
  3. Measure +5 V, +12 V, −12 V and −5 V with the machine running.
  4. Recap the supply if it has not been done.
  5. Clean the floppy heads and test a read and a write.
  6. Check the SIMMs are non-parity and seated.
  7. Back up the internal hard disk.
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References

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  1. ↑ 1.0 1.1 Atari Corporation, Atari MEGA STE Coprocessor Installation Kit, C302228-001 Rev A, 1991, pp. 1–3. Hosted as File:Atari Mega STE Coprocessor Installation Kit.pdf.
  2. ↑ 2.0 2.1 2.2 Atari Corporation, Atari MEGA STE 1.44 Megabyte Floppy Drive Installation Manual, C302953-001 Rev A, 1991, pp. 1–3. Hosted as Atari Mega STE 1.44MB Floppy Drive Installation Manual.
  3. ↑ 3.0 3.1 3.2 3.3 3.4 3.5 "Atari Mega STE", atari-computermuseum.de, last edited 24 August 2024, https://www.atari-computermuseum.de/megaste.htm. Secondary source.
  4. ↑ Pacman, "How to: recapping the Mega STe power supply", exxos's Atari, Amiga & retro forum, 16 October 2017. Community source.
  5. ↑ 5.0 5.1 Atari Corporation, MEGA STE Computer Owner's Manual, appendix D, "Troubleshooting and preventive maintenance". Hosted as File:Atari Mega STE Owner's Manual C302016-001 Rev B.pdf.
  6. ↑ 6.0 6.1 6.2 6.3 6.4 Atari Corporation, Mega STE Schematic, revision 2, April 1990. Sheet 2, power connector J201, fuse F21 and fan header J291; sheet 3, keyboard socket J303 and fuse F31; sheet 4, real-time clock U402, battery connector J401 and diode D401. Hosted as File:Atari Mega STE Schematic Rev 2.pdf.
  7. ↑ François Planque, "How to replace the RTC battery of an Atari Mega STE in 2024", fplanque.com, 14 September 2024. Community source.
  8. ↑ Atari Corporation, Atari TT030 Computer Field Service Manual, C302483-001, August 1991, section 1.4.1 (power supply rating) and section 7 (power supply C302074-001, Phihong PSM-5341). Hosted as Atari TT030 Computer Field Service Manual.
  9. ↑ exxos, "ATARI PSU REPAIR", The LaST Upgrade, part 6, section "MSTE PSU Phihong PSM-5341". Community source.
  10. ↑ 10.0 10.1 10.2 exxos, "MANDATORY FIXES", exxos's Atari, Amiga & retro forum, 31 January 2019. Community source; items 2, 4, 8 and 10.
  11. ↑ Atari Corporation, MEGA STE Computer Owner's Manual, appendix C, "Advanced hard disk utilities". Hosted as File:Atari Mega STE Owner's Manual C302016-001 Rev B.pdf.
  12. ↑ Atari Corporation, Mega STE Schematic, revision 2, April 1990, sheet 7, SIMM sockets U701–U704. Hosted as File:Atari Mega STE Schematic Rev 2.pdf.
  13. ↑ "Mega ST keyboard cable replacement", exxos's Atari, Amiga & retro forum, January 2020. Community source.


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