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[[Category:Atari Capacitor Replacement Guides]]
[[Category:Atari Capacitor Replacement Guides]]
[[Category:Atari Systems]]

Latest revision as of 17:22, 29 March 2026

This guide provides complete capacitor lists and replacement procedures for the Atari 520ST, 520STM, 520STF, 520STFM, 1040ST, 1040STF, and 1040STFM computers. These machines share common motherboard designs — notably the C070789-001 board which is used in both the 520STFM and 1040STFM. Capacitor lists are organised by board revision, as the component count and values vary between revisions.

For the Atari STE range (520STE / 1040STE), see Atari STE Capacitor Replacement Guide.

When to Recap

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With these machines now 35–40 years old, electrolytic capacitors are the most common point of failure. Symptoms of failing capacitors include:

  • Unstable or low +5V supply voltage (PSU caps)
  • Random crashes or freezes
  • Screen dimming when the floppy drive is accessed (PSU peak power)
  • Audio distortion, hum, or crackling
  • Floppy read/write errors
  • Video noise, ghosting, or wavy lines

The PSU should be recapped as a first priority, as failing PSU capacitors can cause symptoms that mimic motherboard faults. Motherboard recapping is a secondary priority — the axial electrolytic capacitors used on ST motherboards (often Wang's brand) have generally proven durable, but replacement is recommended as preventive maintenance.

Safety Warning

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The internal PSU (1040ST/STF/STFM models) contains mains-voltage components. Capacitors on the high-voltage side of the PSU can retain lethal charge even after the machine is unplugged. Only experienced individuals should service the PSU. Allow at least 5 minutes after unplugging before touching any PSU components.

Tools Required

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  • Temperature-controlled soldering iron (chisel tip recommended, 350–370°C)
  • Solder sucker and/or desoldering braid
  • Quality replacement capacitors (Nichicon, Rubycon, Panasonic recommended; low-ESR types for PSU)
  • Digital multimeter for post-recap voltage verification
  • Isopropyl alcohol (99%+) and brush for flux cleanup

Motherboard Capacitor Lists

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Identify your motherboard revision by the part number printed on the PCB. The following lists cover all known ST/STF/STFM motherboard revisions.[1]

C070243 Rev B (520ST / 520STM)

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Early short-case board used in the 520ST and 520STM.

Ref. Designator Capacitance Voltage Type Notes
C31 1 µF 50V Electrolytic
C33 47 µF 25V Electrolytic
C34 1 µF 50V Electrolytic
C50 22 µF 16V Electrolytic
C55 22 µF 16V Electrolytic
— 470 µF 16V Electrolytic Not designated on silkscreen
KBD 100 µF 25V Electrolytic Keyboard controller board

C070243 Rev C (520ST)

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Ref. Designator Capacitance Voltage Type Notes
C31 100 µF 25V Electrolytic
C33 47 µF 25V Electrolytic
C34 47 µF 16V Electrolytic
C50 22 µF 16V Electrolytic
C55 22 µF 16V Electrolytic
C?? 470 µF 16V Electrolytic Designator unclear on PCB
C105 22 µF 16V Electrolytic
— 470 µF 16V Electrolytic Not designated
KBD 100 µF 25V Electrolytic, axial Keyboard controller board

C070243 Rev H (520ST / 520STM)

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Ref. Designator Capacitance Voltage Type Notes
C31 100 µF 16V Electrolytic
C33 47 µF 16V Electrolytic
C34 47 µF 16V Electrolytic
C50 22 µF 16V Electrolytic
C55 22 µF 16V Electrolytic
C56 470 µF 16V Electrolytic May be marked C56 or unmarked
C104 470 µF 16V Electrolytic
C105 22 µF 16V Electrolytic
KBD 100 µF 25V Electrolytic, axial Keyboard controller board

C070523-001 Rev B / Rev C (1040STF)

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Earlier 1040STF-specific board design.

Ref. Designator Capacitance Voltage Type Notes
C7 22 µF 16V Electrolytic
C8 22 µF 16V Electrolytic
C9 47 µF 16V Electrolytic
C12 1 µF 50V Non-polarised 25V replacement acceptable
C14 1 µF 50V Non-polarised 25V replacement acceptable
C25 4.7 µF 25V Electrolytic
C27 4.7 µF 25V Electrolytic
C29 4.7 µF 35V Non-polarised 25V replacement acceptable
C30 4.7 µF 25V Electrolytic
C35 470 µF 16V Electrolytic
C48 100 µF 25V Electrolytic
C71 22 µF 16V Electrolytic
C105 470 µF 16V Electrolytic

C070523-001 Rev D (1040STF / 520STFM)

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Applies to Rev D boards with a large 2200 µF cap at C35.

Ref. Designator Capacitance Voltage Type Notes
C7 22 µF 16V Electrolytic
C8 22 µF 16V Electrolytic
C9 47 µF 16V Electrolytic
C12 100 µF 16V Electrolytic
C14 47 µF 16V Electrolytic
C25 4.7 µF 25V Electrolytic
C27 4.7 µF 25V Electrolytic
C29 4.7 µF 35V Non-polarised 25V replacement acceptable
C30 4.7 µF 25V Electrolytic
C35 2200 µF 16V Electrolytic Large axial or radial cap
C71 22 µF 16V Electrolytic
C105 470 µF 16V Electrolytic
— 100 µF 16V Electrolytic Add-on above C41 (not soldered to C41 pads)

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

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This is the most commonly encountered board revision. It is shared between the 520STFM and 1040STFM — the only difference is RAM population (512 KB vs 1 MB). Also compatible with Rev B, Rev D, and Rev F2 boards based on board photos.[1]

Ref. Designator Capacitance Voltage Type Notes
C2 22 µF 16V Electrolytic
C7 22 µF 16V Electrolytic
C9 47 µF 16V Electrolytic
C11 100 µF 16V Electrolytic
C12 47 µF 16V Electrolytic
C22 100 µF 16V Electrolytic
C49 1000 µF 16V Electrolytic Main bulk decoupling
C70 100 µF 16V Electrolytic
C73 100 µF 16V Electrolytic
C74 4.7 µF 35V Non-polarised Radial replacement provided in kits
C75 4.7 µF 35V Electrolytic
C92 100 µF 16V Electrolytic
C148 100 µF 16V Electrolytic
C149 4700 µF 16V Electrolytic Large main filter capacitor
C215 1 µF 50V Electrolytic Audio path
C216 10 µF 16V Electrolytic Audio path
C217 10 µF 16V Electrolytic Audio path
C218 10 µF 16V Electrolytic Audio path
C219 33 µF 16V Electrolytic Audio path
C220 100 µF 16V Electrolytic Audio path
C221 100 µF 16V Electrolytic Audio path
C223 470 µF 16V Electrolytic

Total: 22 electrolytic capacitors on the motherboard.

C103225 Rev 1 / Rev 2 (1040STFM)

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Late-production board.

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

C103572 Rev 1 (1040STFM)

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Final production board. Identical to C103225 but with one additional cap:

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

PSU Capacitor Lists

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The 1040ST's internal PSU is the most failure-prone component. The 520ST uses an external PSU that is generally more reliable but should still be checked. Below are lists for the most common internal PSU models found in the 1040STF and 1040STFM.

Mitsumi SR98 / SR118 / 68-4231A (220–240V)

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The most common PSU in European 1040STs. Main switching transistor: 2SC2979 (800V, 3A, 40W).[2]

Ref. Designator Original Value Voltage Recommended Replacement Notes
C104 47 µF 400V 68 µF 400V High-voltage primary filter
C201 2200 µF 10V 4700 µF 16V Secondary filter
C202 2200 µF 16V 4700 µF 16V Secondary filter
C203 2200 µF 10V 4700 µF 16V Secondary filter
C204 1000 µF 16V 1500 µF 16V Secondary filter
C205 1000 µF 10V 1500 µF 16V Secondary filter
C206 1 µF 50V 1 µF 50V ceramic Feedback loop; consider ceramic replacement

Also recommended: Replace the bridge rectifier with a KBU1005 (10A, 600V) or similar higher-rated part. The original 2A rectifier is marginal.[2]

Mitsumi SR97 / 68-4242A (110–120V)

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US market PSU.

Ref. Designator Original Value Voltage Recommended Replacement Notes
C104 220 µF 200V 220 µF 200V Primary filter
C201 2200 µF 16V 4700 µF 16V
C202 2200 µF 10V 4700 µF 16V
C203 1000 µF 16V 1500 µF 16V
C204 2200 µF 10V 4700 µF 16V
C205 1000 µF 10V 1500 µF 16V
C206 1 µF 50V 1 µF 50V

ASTEC ASP34 / ASPF34 (220–240V)

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Common European PSU with BU508A main transistor. Multiple sub-revisions (Rev 1–6) exist with minor differences.[1]

Ref. Designator Original Value Voltage Recommended Replacement Notes
C4 47 µF 250V 47 µF 250V Primary filter
C5 47 µF 250V 47 µF 250V Primary filter
C7 330 µF 25V (or 35V) 680 µF 35V Secondary
C9 100 µF 25V 100 µF 25V
C12 2200 µF 16V 4700 µF 16V
C13 4700 µF 16V 4700 µF 16V
C14 330 µF 25V (or 35V) 680 µF 35V
C15 330 µF 25V (or 35V) 680 µF 35V

DVE DSP-508A / DSP-508AA (220–240V)

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Uses BU508A transistor. Generally good regulation even with aged caps.[2]

Ref. Designator Original Value Voltage Recommended Replacement Notes
C3 47 µF 250V 47 µF 250V Primary
C4 47 µF 250V 47 µF 250V Primary
C8 330 µF 25V 680 µF 25V
C9 1 µF 50V 1 µF 50V
C?? 100 µF 25V 100 µF 25V In shrinkwrap near safety cap at board top
C20 330 µF 25V 680 µF 25V
C22 2200 µF 16V 4700 µF 16V
C23 330 µF 25V 680 µF 25V
C25 2200 µF 16V 4700 µF 16V

FPK-N3 5657-B001-1

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Ref. Designator Capacitance Voltage Notes
C5 220 µF 200V Primary
C8 47 µF 16V
C9 47 µF 16V
C101 470 µF 25V
C102 470 µF 25V
C103 100 µF 25V
C201 2200 µF 10V
C202 2200 µF 10V
C203 470 µF 10V
C205 — — Empty position on PCB
C303 1 µF 50V

C070091-014 / Model 1103 (520ST External PSU)

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Designators not available for this external PSU. Replace by value:

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

Internal Floppy Drive Capacitors (1040ST)

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The 1040ST's internal floppy drive (commonly the TDK D357 / T41V) also contains electrolytic capacitors that can fail:

Capacitance Voltage Quantity Notes
22 µF 16V 2
47 µF 16V 2
10 µF 25V 1
4.7 µF 35V 1
2.2 µF 50V 1
0.47 µF 50V 5 May be film or ceramic on some drives
3.3 µF 50V 1

Replacement Procedure

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General Tips

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  1. Always note polarity before removing old caps. The negative stripe on the capacitor body and the polarity markings on the PCB silkscreen should match. If the silkscreen is unclear, photograph the board before starting.
  2. Use quality replacement capacitors. Panasonic FR series, Nichicon, and Rubycon are recommended. Avoid cheap unbranded capacitors, particularly for the PSU — poor ESR characteristics can cause the PSU to malfunction or even damage components.
  3. Axial to radial conversion: Many ST motherboard caps are axial (leads from each end). Modern replacements are commonly radial (both leads from the same end). Radial caps can be used in axial positions by bending the leads appropriately, or by mounting them upright.[1]
  4. Non-polarised (NP) capacitors: Several positions (notably C74 on the C070789-001 board and C29 on the C070523-001 board) require non-polarised electrolytic capacitors. These can be replaced with bipolar/non-polarised electrolytics or with appropriately rated film capacitors.

PSU Recap Procedure (1040ST)

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  1. Unplug the machine and wait at least 5 minutes.
  2. Remove the top case and disconnect the PSU from the motherboard.
  3. Remove the PSU from the case (typically held by screws and/or clips).
  4. Remove the metal PSU shield (if present) — usually held by bent tabs.
  5. Photograph the PCB before starting, noting all capacitor polarities and positions.
  6. Desolder each capacitor one at a time, clean the pads, and solder in the replacement.
  7. For the bridge rectifier replacement: The replacement may have a different pinout. Triple-check the + and − markings match the PCB before powering on. An incorrectly installed rectifier will destroy the PSU.
  8. Reassemble the PSU shield and reinstall in the case.

Motherboard Recap Procedure

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  1. With the machine open and PSU disconnected, work through each capacitor position.
  2. Desolder the old cap, clean the pads with desoldering braid, and solder in the replacement.
  3. Pay attention to the large C149 (4700 µF on C070789-001 boards) — this is a physically large cap and removing it cleanly requires adequate desoldering.
  4. After completing all replacements, clean the board with IPA to remove flux residue.

Post-Recap Voltage Checks

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After recapping, verify the following before reconnecting any peripherals:

Test Point Expected Value Tolerance Notes
+5V at motherboard power header 5.00V ±0.25V Measure with machine powered on and under normal load. Adjust PSU trim pot if available.
+12V at motherboard power header 12.0V ±1.0V Needed for floppy and RS-232.
+5V ripple (oscilloscope) <200 mV pk-pk — Indicates healthy PSU caps. >500 mV indicates a problem remains.
+5V at CPU VCC pin 4.90V – 5.10V — Check for excessive voltage drop from power header to CPU.

If the PSU has a voltage adjustment trimmer (present on some Mitsumi and ASTEC models), set the +5V output to 5.00V–5.10V under load. Do not exceed 5.25V.

Sourcing Capacitor Kits

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Pre-assembled capacitor kits for specific board revisions are available from:

  • Console5 (console5.com) — Kits for most ST motherboard and PSU revisions
  • exxos (exxosforum.co.uk/atari/store2) — PSU recap kits and replacement PSU boards

When sourcing individual capacitors, use reputable suppliers (Farnell/Element14, Mouser, Digikey, RS Components) to avoid counterfeit or low-quality parts.

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References

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  1. ↑ 1.0 1.1 1.2 1.3 Atari ST Cap Lists, Console5 TechWiki—link(accessed 2026-03-27)
  2. ↑ 2.0 2.1 2.2 The LaST Upgrade - Atari PSU Repair, exxos—link(accessed 2026-03-27)


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