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Atari ST Capacitor Replacement Guide

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This guide provides complete capacitor lists for the Atari 520ST and Atari 1040ST motherboards and power supplies, covering the 520STF, 520STFM, 1040STF, and 1040STFM variants. The 520ST and 1040ST share several board designs (the C070789 board was used for both 520STFM and 1040STFM), so capacitor lists are organised by board revision number rather than by model name. Identify your specific board revision before ordering parts.

Why Recap?

Electrolytic capacitors degrade over time. After 30+ years, the electrolyte dries out, ESR (equivalent series resistance) increases, and capacitance drops. This degradation causes:

  • Increased voltage ripple on power rails, leading to instability and random crashes
  • High-voltage spikes passing through to the motherboard (especially from the PSU), which can damage custom ICs
  • Reduced peak current delivery (causing problems when loads change suddenly, such as floppy drive motor spin-up)
  • Audio distortion (on models with audio output filtering capacitors)

The PSU capacitors are the highest priority for replacement. Original Atari ST PSUs typically used low-quality capacitors that have not aged well. Motherboard capacitors are lower priority — many were higher-quality Wang/Chang brand parts that have held up better — but a full recap is still recommended as preventive maintenance.[1]

Identifying Your Board Revision

The board revision number is printed directly on the PCB, typically along one edge or near the cartridge port area. Common boards found in the 520ST and 1040ST:

Board Number Revisions Used In
C070243 Rev B, C, H 520ST, 520STF (early models, no RF modulator)
C070523-001 Rev B, C, D 1040STF (dedicated 1040 board)
C070789-001 Rev C, D, F 520STFM and 1040STFM (unified board, with RF modulator)
C103225 Rev 1, 2 520STFM and 1040STFM (late production)
C103572 Rev 1 520STFM and 1040STFM (final production revision)

Motherboard Capacitor Lists

All capacitors listed are electrolytic unless marked "NP" (non-polarised / bipolar). Replace with equivalent or higher voltage rating. Capacitance values should match; a slightly higher capacitance is acceptable. Use 105°C rated capacitors for longer service life.

C070243 Rev B (520ST / 520STF early)

Ref. Value Voltage Notes
C31 1 µF 50 V
C33 47 µF 25 V
C34 1 µF 50 V
C50 22 µF 16 V
C55 22 µF 16 V
(unmarked) 470 µF 16 V Bulk decoupling, not at a labelled position
KBD 100 µF 25 V On the keyboard connector area

[2]

C070243 Rev C (520ST / 520STF)

Ref. Value Voltage Notes
C31 100 µF 25 V
C33 47 µF 25 V
C34 47 µF 16 V
C50 22 µF 16 V
C55 22 µF 16 V
C?? 470 µF 16 V Position varies
C105 22 µF 16 V
(unmarked) 470 µF 16 V Bulk decoupling
KBD 100 µF 25 V Axial type

C070243 Rev H (520ST / 520STF)

Ref. Value Voltage Notes
C31 100 µF 16 V
C33 47 µF 16 V
C34 47 µF 16 V
C50 22 µF 16 V
C55 22 µF 16 V
C56 470 µF 16 V May not be populated on all boards
C104 470 µF 16 V
C105 22 µF 16 V
KBD 100 µF 25 V Axial type

C070523-001 Rev B / C (1040STF)

Ref. Value Voltage Notes
C7 22 µF 16 V
C8 22 µF 16 V
C9 47 µF 16 V
C12 1 µF 50 V Non-polarised (25 V parts acceptable)
C14 1 µF 50 V Non-polarised (25 V parts acceptable)
C25 4.7 µF 25 V
C27 4.7 µF 25 V
C29 4.7 µF 35 V Non-polarised (25 V parts acceptable)
C30 4.7 µF 25 V
C35 470 µF 16 V
C48 100 µF 25 V
C71 22 µF 16 V
C105 470 µF 16 V

C070523-001 Rev D (1040STF)

Note: Rev D boards have a large 2200 µF axial or radial capacitor at C35 instead of the 470 µF found on Rev B/C.

Ref. Value Voltage Notes
C7 22 µF 16 V
C8 22 µF 16 V
C9 47 µF 16 V
C12 100 µF 16 V
C14 47 µF 16 V
C25 4.7 µF 25 V
C27 4.7 µF 25 V
C29 4.7 µF 35 V Non-polarised (25 V parts acceptable)
C30 4.7 µF 25 V
C35 2200 µF 16 V Large axial or radial — confirm physical fit
C71 22 µF 16 V
C105 470 µF 16 V
(added) 100 µF 16 V Factory-added above C41, not on C41 pads

C070789-001 Rev C / F (520STFM / 1040STFM)

This is the most common board found in both 520STFM and 1040STFM machines. The same PCB layout is used for both; the difference is the number of populated DRAM chips (8 for 520, 16 for 1040).

Ref. Value Voltage Notes
C2 22 µF 16 V
C7 22 µF 16 V
C9 47 µF 16 V
C11 100 µF 16 V
C12 47 µF 16 V
C22 100 µF 16 V
C49 1000 µF 16 V Main bulk decoupling
C70 100 µF 16 V
C73 100 µF 16 V
C74 4.7 µF 35 V Non-polarised
C75 4.7 µF 35 V
C92 100 µF 16 V
C148 100 µF 16 V
C149 4700 µF 16 V Large bulk capacitor
C215 1 µF 50 V
C216 10 µF 16 V
C217 10 µF 16 V
C218 10 µF 16 V
C219 33 µF 16 V
C220 100 µF 16 V
C221 100 µF 16 V
C223 470 µF 16 V

C103225 Rev 1 / Rev 2 (520STFM / 1040STFM late)

Ref. Value Voltage Notes
C2 22 µF 16 V
C7 22 µF 16 V
C9 47 µF 16 V
C11 100 µF 16 V
C12 47 µF 16 V
C49 1000 µF 16 V
C70 100 µF 16 V
C73 100 µF 16 V
C74 4.7 µF 35 V Non-polarised
C75 4.7 µF 35 V
C92 100 µF 16 V
C148 100 µF 16 V
C149 4700 µF 16 V

C103572 Rev 1 (520STFM / 1040STFM final)

Ref. Value Voltage Notes
C2 22 µF 16 V
C7 22 µF 16 V
C9 47 µF 16 V
C11 100 µF 16 V
C12 47 µF 16 V
C49 1000 µF 16 V
C70 100 µF 16 V
C73 100 µF 16 V
C74 4.7 µF 35 V Non-polarised
C75 4.7 µF 35 V
C92 100 µF 16 V
C148 100 µF 16 V
C149 4700 µF 16 V
C190 100 µF 16 V Additional cap not present on C103225

Power Supply Capacitor Lists

PSU recapping is the single most important maintenance step for the 520ST and 1040ST. The PSU should be recapped before the motherboard. Identify your PSU model from the label on the PSU PCB or enclosure.

Warning: PSU capacitors on the primary (mains) side carry high voltage ratings (200–400 V). Use capacitors rated for the correct or higher voltage. Do not substitute lower-voltage parts. Observe correct polarity — a reversed high-voltage electrolytic can fail explosively.

Mitsumi SR97 / 68-4242A (110–120 V, 1040STF North America)

Ref. Value Voltage Notes
C104 220 µF 200 V Primary side, high voltage
C201 2200 µF 16 V Secondary, +5 V rail
C202 2200 µF 10 V Secondary
C203 1000 µF 16 V Secondary
C204 2200 µF 10 V Secondary
C205 1000 µF 10 V Secondary
C206 1 µF 50 V Feedback/timing

[3]

Mitsumi SR98 / SR118 / 68-4231A (220–240 V, European 520STFM / 1040STFM)

Ref. Value Voltage Notes
C104 47 µF 400 V Primary side, high voltage
C201 2200 µF 10 V Secondary
C202 2200 µF 16 V Secondary, +5 V rail
C203 2200 µF 10 V Secondary
C204 1000 µF 16 V Secondary
C205 1000 µF 10 V Secondary
C206 1 µF 50 V Feedback/timing

The SR98 is the most commonly encountered PSU in European ST machines and is known to degrade significantly with age. exxos research has documented SR98 PSUs producing AC-like ripple waveforms on the +5 V rail due to capacitor failure.[4]

Astec ASP34 / ASPF34-1 (1040STF / 1040STFM)

Ref. Value Voltage Notes
C4 47 µF 250 V Primary side
C5 47 µF 250 V Primary side
C7 330 µF 25 V (sometimes 35 V original; use 35 V replacements)
C9 100 µF 25 V
C12 2200 µF 16 V Secondary bulk
C13 4700 µF 16 V Secondary bulk, +5 V rail
C14 330 µF 25 V (sometimes 35 V original; use 35 V replacements)
C15 330 µF 25 V (sometimes 35 V original; use 35 V replacements)

DVE DSP-508A / DSP-508AA (520STFM / 1040STFM)

Note: The schematic parts list for this PSU differs from production units. The list below is based on actual production hardware.

Ref. Value Voltage Notes
C3 47 µF 250 V Primary side
C4 47 µF 250 V Primary side
C8 330 µF 25 V
C9 1 µF 50 V
C?? 100 µF 25 V In shrinkwrap near safety cap at board top
C22 2200 µF 16 V Secondary bulk
C25 2200 µF 16 V Secondary bulk
C23 330 µF 25 V
C20 330 µF 25 V

FPK-N3 5657-B001-1 (520STFM European)

Ref. Value Voltage Notes
C5 220 µF 200 V Primary side
C8 47 µF 16 V
C9 47 µF 16 V
C101 470 µF 25 V
C103 100 µF 25 V
C201 2200 µF 10 V Secondary
C202 2200 µF 10 V Secondary
C203 470 µF 10 V
C102 470 µF 25 V
C205 EMPTY — Position not populated from factory
C303 1 µF 50 V

Skynet ATR-1886 (520ST / 1040STF, 120 V North America)

Reference designators are not available for this PSU. Replace by value:

Value Voltage Quantity
68 µF 200 V 2
1000 µF 25 V 1
1000 µF 10 V 1
330 µF 25 V 1
120 µF 25 V 1
470 µF 25 V 2

Model 1103 / C070091-014 (Early 520ST, 110 V)

Reference designators are not available for this PSU. Replace by value:

Value Voltage Quantity
4700 µF 16 V 1
2200 µF 25 V 1
100 µF 25 V 1
220 µF 25 V 1
10 µF 25 V 1

Internal Floppy Drive Capacitors

The most common internal floppy drive found in the 1040STF/STFM is the TDK D357 (T41V). Reference designators are not printed on the drive PCB; replace by value.

Value Voltage Quantity Notes
22 µF 16 V 2
47 µF 16 V 2
10 µF 25 V 1
4.7 µF 35 V 1
2.2 µF 50 V 1
0.47 µF 50 V 5 Film type recommended
3.3 µF 50 V 1

Recapping Procedure

Tools and Materials

  • Temperature-controlled soldering iron (recommended 300–350°C for lead-free, 280–320°C for leaded solder)
  • Solder sucker (spring-loaded) or desoldering braid/wick
  • Fresh solder (60/40 Sn/Pb for leaded, or SAC305 for lead-free)
  • Replacement capacitors (see lists above)
  • Multimeter for post-recap voltage verification
  • Isopropyl alcohol (99%) and brush for cleaning flux residue

Step-by-Step (Motherboard)

  1. Identify all electrolytic capacitors on the board and cross-reference with the appropriate cap list above.
  2. Note the polarity of each capacitor before removal. The negative stripe is on the can; the positive leg goes through the pad marked "+" on the PCB (not all boards mark polarity clearly — photograph before removal).
  3. Heat one leg of the old capacitor and gently pull while the solder melts. Repeat for the other leg. Alternatively, use desoldering braid to remove solder from both pads first, then lift the capacitor out.
  4. Clean the through-holes with the solder sucker or braid until clear.
  5. Insert the new capacitor, observing correct polarity.
  6. Solder both legs, using enough solder to form a good concave fillet.
  7. Trim excess lead length.
  8. After all capacitors are replaced, clean flux residue with IPA and a brush.

Step-by-Step (PSU)

Mains-side safety: The primary-side capacitors (those rated 200 V and above) can retain a lethal charge. Before working on the PSU:

  1. Disconnect from mains.
  2. Switch the power switch to ON and wait 5 minutes to allow capacitors to discharge through internal bleeder resistors.
  3. Measure voltage across the large primary capacitor(s) with a multimeter set to DC volts. It should read 0 V. If it does not, discharge manually through a 10 kΩ / 5 W resistor.

Follow the same removal and replacement procedure as for the motherboard. Pay special attention to the physical size of replacement capacitors — PSU enclosures have limited space. Ensure replacement capacitors are rated for the correct temperature (105°C recommended) and have appropriate ripple current ratings.

Post-Recap Voltage Verification

After recapping the PSU, always test with a dummy load before connecting to the motherboard:

Test Method Expected Result
+5 V DC Multimeter across red wire and black wire at PSU output connector, with 2.2 Ω / 17 W dummy load 4.90–5.10 V (should be tighter than pre-recap)
+12 V DC Multimeter across blue wire and black wire, with 10 Ω / 17 W dummy load 11.0–13.0 V
+5 V ripple Oscilloscope AC-coupled on +5 V rail, with dummy load Under 50 mV peak-to-peak (a well-recapped PSU should achieve this; original spec was often 100–200 mV)
+12 V ripple Oscilloscope AC-coupled on +12 V rail, with dummy load Under 100 mV peak-to-peak

After confirming acceptable PSU voltages, reconnect to the motherboard and verify:

  1. Machine boots to GEM desktop.
  2. +5 V measured at the motherboard power input header: 4.85–5.15 V.
  3. Floppy drive operates correctly (the motor spin-up is the biggest transient load and will reveal marginal regulation).
  4. No random crashes or visual artefacts during extended use.

Capacitor Upgrade Recommendations

exxos recommends slightly increasing the secondary-side capacitor values in ST PSUs to improve regulation and reduce ripple. This slows the feedback loop slightly, resulting in more stable output voltages and better peak current handling. For example, replacing a 2200 µF / 10 V output capacitor with a 3300 µF / 16 V unit of equivalent physical size will improve regulation without negative side effects.[5]

When upgrading values:

  • Only increase secondary-side (low voltage) capacitors. Do not change primary-side capacitor values.
  • Increase by no more than 50% above original value.
  • Ensure the physical dimensions of the replacement capacitor fit the available space.
  • Use capacitors from reputable manufacturers (Panasonic, Nichicon, Rubycon, United Chemi-Con).

Parts Sourcing

Pre-made capacitor kits for all Atari ST board revisions and PSU models are available from:

  • Console5 (console5.com) — Board-specific and PSU-specific kits with all required capacitors.
  • exxos (exxosforum.co.uk/atari/store2) — PSU recap kits with upgraded values, plus replacement PSU boards.
  • Individual components from Mouser, Digikey, Farnell, or RS Components.

See Also

References

  1. ↑ Atari ST PSU Capacitor & Upgrade Information, exxos Forum—link(accessed 2026-03-27)
  2. ↑ Atari ST – Cap Lists, Console5 TechWiki—link(accessed 2026-03-27)
  3. ↑ Atari ST – Power Supply Cap Lists, Console5 TechWiki—link(accessed 2026-03-27)
  4. ↑ Atari ST PSU Capacitor & Upgrade Information, exxos Forum—link(accessed 2026-03-27)
  5. ↑ Atari ST PSU Capacitor & Upgrade Information, exxos Forum—link(accessed 2026-03-27)


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