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{{Infobox guide
This guide provides complete capacitor lists and replacement procedures for the '''Atari [[Atari 520ST|520ST]]''', '''[[Atari 520STM|520STM]]''', '''[[Atari 520STF|520STF]]''', '''[[Atari 520STFM|520STFM]]''', '''[[Atari 1040ST|1040ST]]''', '''[[Atari 1040STF|1040STF]]''', and '''[[Atari 1040STFM|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.
|title=Atari ST Capacitor Replacement Guide
|image=
|applies_to=[[Atari 520ST]], [[Atari 1040ST]]
|skill_level=Intermediate (through-hole soldering required)
|tools_required=Soldering iron (temperature-controlled), solder sucker/desoldering braid, multimeter, fresh solder (60/40 or lead-free), replacement capacitors
}}


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


== Why Recap? ==
== When to Recap ==


Electrolytic capacitors degrade over time. After 30+ years, the electrolyte dries out, ESR (equivalent series resistance) increases, and capacitance drops. This degradation causes:
With these machines now 35–40 years old, electrolytic capacitors are the most common point of failure. Symptoms of failing capacitors include:


* Increased voltage ripple on power rails, leading to instability and random crashes
* Unstable or low +5V supply voltage (PSU caps)
* High-voltage spikes passing through to the motherboard (especially from the PSU), which can damage custom ICs
* Random crashes or freezes
* Reduced peak current delivery (causing problems when loads change suddenly, such as floppy drive motor spin-up)
* Screen dimming when the floppy drive is accessed (PSU peak power)
* Audio distortion (on models with audio output filtering capacitors)
* Audio distortion, hum, or crackling
* Floppy read/write errors
* Video noise, ghosting, or wavy lines


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.<ref>{{cite web |url=https://www.exxosforum.co.uk/forum/viewtopic.php?t=25 |title=Atari ST PSU Capacitor & Upgrade Information |publisher=exxos Forum |access-date=2026-03-27}}</ref>
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.


== Identifying Your Board Revision ==
== Safety Warning ==


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:
'''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.'''


<templatestyles src="Template:StyledTable/styles.css" />
== Tools Required ==
{| class="wikitable styled-table"
 
! Board Number !! Revisions !! Used In
* Temperature-controlled soldering iron (chisel tip recommended, 350–370°C)
|-
* Solder sucker and/or desoldering braid
| C070243 || Rev B, C, H || 520ST, 520STF (early models, no RF modulator)
* Quality replacement capacitors (Nichicon, Rubycon, Panasonic recommended; low-ESR types for PSU)
|-
* Digital multimeter for post-recap voltage verification
| C070523-001 || Rev B, C, D || 1040STF (dedicated 1040 board)
* Isopropyl alcohol (99%+) and brush for flux cleanup
|-
| 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 ==
== 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.
Identify your motherboard revision by the part number printed on the PCB. The following lists cover all known ST/STF/STFM motherboard revisions.<ref name="console5">{{cite web |url=https://wiki.console5.com/wiki/Atari_ST |title=Atari ST Cap Lists |publisher=Console5 TechWiki |access-date=2026-03-27}}</ref>


=== C070243 Rev B (520ST / 520STF early) ===
=== C070243 Rev B (520ST / 520STM) ===
 
Early short-case board used in the 520ST and 520STM.


<templatestyles src="Template:StyledTable/styles.css" />
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{| class="wikitable styled-table"
{| class="wikitable styled-table"
! Ref. !! Value !! Voltage !! Notes
! Ref. Designator !! Capacitance !! Voltage !! Type !! Notes
|-
|-
| C31 || 1 µF || 50 V ||
| C31 || 1 µF || 50V || Electrolytic ||
|-
|-
| C33 || 47 µF || 25 V ||
| C33 || 47 µF || 25V || Electrolytic ||
|-
|-
| C34 || 1 µF || 50 V ||
| C34 || 1 µF || 50V || Electrolytic ||
|-
|-
| C50 || 22 µF || 16 V ||
| C50 || 22 µF || 16V || Electrolytic ||
|-
|-
| C55 || 22 µF || 16 V ||
| C55 || 22 µF || 16V || Electrolytic ||
|-
|-
| (unmarked) || 470 µF || 16 V || Bulk decoupling, not at a labelled position
| — || 470 µF || 16V || Electrolytic || Not designated on silkscreen
|-
|-
| KBD || 100 µF || 25 V || On the keyboard connector area
| KBD || 100 µF || 25V || Electrolytic || Keyboard controller board
|}<ref>{{cite web |url=https://wiki.console5.com/wiki/Atari_ST |title=Atari ST – Cap Lists |publisher=Console5 TechWiki |access-date=2026-03-27}}</ref>
|}


=== C070243 Rev C (520ST / 520STF) ===
=== C070243 Rev C (520ST) ===


<templatestyles src="Template:StyledTable/styles.css" />
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{| class="wikitable styled-table"
{| class="wikitable styled-table"
! Ref. !! Value !! Voltage !! Notes
! Ref. Designator !! Capacitance !! Voltage !! Type !! Notes
|-
|-
| C31 || 100 µF || 25 V ||
| C31 || 100 µF || 25V || Electrolytic ||
|-
|-
| C33 || 47 µF || 25 V ||
| C33 || 47 µF || 25V || Electrolytic ||
|-
|-
| C34 || 47 µF || 16 V ||
| C34 || 47 µF || 16V || Electrolytic ||
|-
|-
| C50 || 22 µF || 16 V ||
| C50 || 22 µF || 16V || Electrolytic ||
|-
|-
| C55 || 22 µF || 16 V ||
| C55 || 22 µF || 16V || Electrolytic ||
|-
|-
| C?? || 470 µF || 16 V || Position varies
| C?? || 470 µF || 16V || Electrolytic || Designator unclear on PCB
|-
|-
| C105 || 22 µF || 16 V ||
| C105 || 22 µF || 16V || Electrolytic ||
|-
|-
| (unmarked) || 470 µF || 16 V || Bulk decoupling
| — || 470 µF || 16V || Electrolytic || Not designated
|-
|-
| KBD || 100 µF || 25 V || Axial type
| KBD || 100 µF || 25V || Electrolytic, axial || Keyboard controller board
|}
|}


=== C070243 Rev H (520ST / 520STF) ===
=== C070243 Rev H (520ST / 520STM) ===


<templatestyles src="Template:StyledTable/styles.css" />
<templatestyles src="Template:StyledTable/styles.css" />
{| class="wikitable styled-table"
{| class="wikitable styled-table"
! Ref. !! Value !! Voltage !! Notes
! Ref. Designator !! Capacitance !! Voltage !! Type !! Notes
|-
|-
| C31 || 100 µF || 16 V ||
| C31 || 100 µF || 16V || Electrolytic ||
|-
|-
| C33 || 47 µF || 16 V ||
| C33 || 47 µF || 16V || Electrolytic ||
|-
|-
| C34 || 47 µF || 16 V ||
| C34 || 47 µF || 16V || Electrolytic ||
|-
|-
| C50 || 22 µF || 16 V ||
| C50 || 22 µF || 16V || Electrolytic ||
|-
|-
| C55 || 22 µF || 16 V ||
| C55 || 22 µF || 16V || Electrolytic ||
|-
|-
| C56 || 470 µF || 16 V || May not be populated on all boards
| C56 || 470 µF || 16V || Electrolytic || May be marked C56 or unmarked
|-
|-
| C104 || 470 µF || 16 V ||
| C104 || 470 µF || 16V || Electrolytic ||
|-
|-
| C105 || 22 µF || 16 V ||
| C105 || 22 µF || 16V || Electrolytic ||
|-
|-
| KBD || 100 µF || 25 V || Axial type
| KBD || 100 µF || 25V || Electrolytic, axial || Keyboard controller board
|}
|}


=== C070523-001 Rev B / C (1040STF) ===
=== C070523-001 Rev B / Rev C (1040STF) ===
 
Earlier 1040STF-specific board design.


<templatestyles src="Template:StyledTable/styles.css" />
<templatestyles src="Template:StyledTable/styles.css" />
{| class="wikitable styled-table"
{| class="wikitable styled-table"
! Ref. !! Value !! Voltage !! Notes
! Ref. Designator !! Capacitance !! Voltage !! Type !! Notes
|-
|-
| C7 || 22 µF || 16 V ||
| C7 || 22 µF || 16V || Electrolytic ||
|-
|-
| C8 || 22 µF || 16 V ||
| C8 || 22 µF || 16V || Electrolytic ||
|-
|-
| C9 || 47 µF || 16 V ||
| C9 || 47 µF || 16V || Electrolytic ||
|-
|-
| C12 || 1 µF || 50 V || Non-polarised (25 V parts acceptable)
| C12 || 1 µF || 50V || Non-polarised || 25V replacement acceptable
|-
|-
| C14 || 1 µF || 50 V || Non-polarised (25 V parts acceptable)
| C14 || 1 µF || 50V || Non-polarised || 25V replacement acceptable
|-
|-
| C25 || 4.7 µF || 25 V ||
| C25 || 4.7 µF || 25V || Electrolytic ||
|-
|-
| C27 || 4.7 µF || 25 V ||
| C27 || 4.7 µF || 25V || Electrolytic ||
|-
|-
| C29 || 4.7 µF || 35 V || Non-polarised (25 V parts acceptable)
| C29 || 4.7 µF || 35V || Non-polarised || 25V replacement acceptable
|-
|-
| C30 || 4.7 µF || 25 V ||
| C30 || 4.7 µF || 25V || Electrolytic ||
|-
|-
| C35 || 470 µF || 16 V ||
| C35 || 470 µF || 16V || Electrolytic ||
|-
|-
| C48 || 100 µF || 25 V ||
| C48 || 100 µF || 25V || Electrolytic ||
|-
|-
| C71 || 22 µF || 16 V ||
| C71 || 22 µF || 16V || Electrolytic ||
|-
|-
| C105 || 470 µF || 16 V ||
| C105 || 470 µF || 16V || Electrolytic ||
|}
|}


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


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


<templatestyles src="Template:StyledTable/styles.css" />
<templatestyles src="Template:StyledTable/styles.css" />
{| class="wikitable styled-table"
{| class="wikitable styled-table"
! Ref. !! Value !! Voltage !! Notes
! Ref. Designator !! Capacitance !! Voltage !! Type !! Notes
|-
|-
| C7 || 22 µF || 16 V ||
| C7 || 22 µF || 16V || Electrolytic ||
|-
|-
| C8 || 22 µF || 16 V ||
| C8 || 22 µF || 16V || Electrolytic ||
|-
|-
| C9 || 47 µF || 16 V ||
| C9 || 47 µF || 16V || Electrolytic ||
|-
|-
| C12 || 100 µF || 16 V ||
| C12 || 100 µF || 16V || Electrolytic ||
|-
|-
| C14 || 47 µF || 16 V ||
| C14 || 47 µF || 16V || Electrolytic ||
|-
|-
| C25 || 4.7 µF || 25 V ||
| C25 || 4.7 µF || 25V || Electrolytic ||
|-
|-
| C27 || 4.7 µF || 25 V ||
| C27 || 4.7 µF || 25V || Electrolytic ||
|-
|-
| C29 || 4.7 µF || 35 V || Non-polarised (25 V parts acceptable)
| C29 || 4.7 µF || 35V || Non-polarised || 25V replacement acceptable
|-
|-
| C30 || 4.7 µF || 25 V ||
| C30 || 4.7 µF || 25V || Electrolytic ||
|-
|-
| C35 || 2200 µF || 16 V || Large axial or radial — confirm physical fit
| C35 || 2200 µF || 16V || Electrolytic || Large axial or radial cap
|-
|-
| C71 || 22 µF || 16 V ||
| C71 || 22 µF || 16V || Electrolytic ||
|-
|-
| C105 || 470 µF || 16 V ||
| C105 || 470 µF || 16V || Electrolytic ||
|-
|-
| (added) || 100 µF || 16 V || Factory-added above C41, not on C41 pads
| — || 100 µF || 16V || Electrolytic || Add-on above C41 (not soldered to C41 pads)
|}
|}


=== C070789-001 Rev C / F (520STFM / 1040STFM) ===
=== C070789-001 Rev C / Rev 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).
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.<ref name="console5"/>


<templatestyles src="Template:StyledTable/styles.css" />
<templatestyles src="Template:StyledTable/styles.css" />
{| class="wikitable styled-table"
{| class="wikitable styled-table"
! Ref. !! Value !! Voltage !! Notes
! Ref. Designator !! Capacitance !! Voltage !! Type !! Notes
|-
|-
| C2 || 22 µF || 16 V ||
| C2 || 22 µF || 16V || Electrolytic ||
|-
|-
| C7 || 22 µF || 16 V ||
| C7 || 22 µF || 16V || Electrolytic ||
|-
|-
| C9 || 47 µF || 16 V ||
| C9 || 47 µF || 16V || Electrolytic ||
|-
|-
| C11 || 100 µF || 16 V ||
| C11 || 100 µF || 16V || Electrolytic ||
|-
|-
| C12 || 47 µF || 16 V ||
| C12 || 47 µF || 16V || Electrolytic ||
|-
|-
| C22 || 100 µF || 16 V ||
| C22 || 100 µF || 16V || Electrolytic ||
|-
|-
| C49 || 1000 µF || 16 V || Main bulk decoupling
| C49 || 1000 µF || 16V || Electrolytic || Main bulk decoupling
|-
|-
| C70 || 100 µF || 16 V ||
| C70 || 100 µF || 16V || Electrolytic ||
|-
|-
| C73 || 100 µF || 16 V ||
| C73 || 100 µF || 16V || Electrolytic ||
|-
|-
| C74 || 4.7 µF || 35 V || Non-polarised
| C74 || 4.7 µF || 35V || Non-polarised || Radial replacement provided in kits
|-
|-
| C75 || 4.7 µF || 35 V ||
| C75 || 4.7 µF || 35V || Electrolytic ||
|-
|-
| C92 || 100 µF || 16 V ||
| C92 || 100 µF || 16V || Electrolytic ||
|-
|-
| C148 || 100 µF || 16 V ||
| C148 || 100 µF || 16V || Electrolytic ||
|-
|-
| C149 || 4700 µF || 16 V || Large bulk capacitor
| C149 || 4700 µF || 16V || Electrolytic || Large main filter capacitor
|-
|-
| C215 || 1 µF || 50 V ||
| C215 || 1 µF || 50V || Electrolytic || Audio path
|-
|-
| C216 || 10 µF || 16 V ||
| C216 || 10 µF || 16V || Electrolytic || Audio path
|-
|-
| C217 || 10 µF || 16 V ||
| C217 || 10 µF || 16V || Electrolytic || Audio path
|-
|-
| C218 || 10 µF || 16 V ||
| C218 || 10 µF || 16V || Electrolytic || Audio path
|-
|-
| C219 || 33 µF || 16 V ||
| C219 || 33 µF || 16V || Electrolytic || Audio path
|-
|-
| C220 || 100 µF || 16 V ||
| C220 || 100 µF || 16V || Electrolytic || Audio path
|-
|-
| C221 || 100 µF || 16 V ||
| C221 || 100 µF || 16V || Electrolytic || Audio path
|-
|-
| C223 || 470 µF || 16 V ||
| C223 || 470 µF || 16V || Electrolytic ||
|}
|}


=== C103225 Rev 1 / Rev 2 (520STFM / 1040STFM late) ===
Total: 22 electrolytic capacitors on the motherboard.
 
=== C103225 Rev 1 / Rev 2 (1040STFM) ===
 
Late-production board.


<templatestyles src="Template:StyledTable/styles.css" />
<templatestyles src="Template:StyledTable/styles.css" />
{| class="wikitable styled-table"
{| class="wikitable styled-table"
! Ref. !! Value !! Voltage !! Notes
! Ref. Designator !! Capacitance !! Voltage !! Type !! Notes
|-
|-
| C2 || 22 µF || 16 V ||
| C2 || 22 µF || 16V || Electrolytic ||
|-
|-
| C7 || 22 µF || 16 V ||
| C7 || 22 µF || 16V || Electrolytic ||
|-
|-
| C9 || 47 µF || 16 V ||
| C9 || 47 µF || 16V || Electrolytic ||
|-
|-
| C11 || 100 µF || 16 V ||
| C11 || 100 µF || 16V || Electrolytic ||
|-
|-
| C12 || 47 µF || 16 V ||
| C12 || 47 µF || 16V || Electrolytic ||
|-
|-
| C49 || 1000 µF || 16 V ||
| C49 || 1000 µF || 16V || Electrolytic ||
|-
|-
| C70 || 100 µF || 16 V ||
| C70 || 100 µF || 16V || Electrolytic ||
|-
|-
| C73 || 100 µF || 16 V ||
| C73 || 100 µF || 16V || Electrolytic ||
|-
|-
| C74 || 4.7 µF || 35 V || Non-polarised
| C74 || 4.7 µF || 35V || Non-polarised ||
|-
|-
| C75 || 4.7 µF || 35 V ||
| C75 || 4.7 µF || 35V || Electrolytic ||
|-
|-
| C92 || 100 µF || 16 V ||
| C92 || 100 µF || 16V || Electrolytic ||
|-
|-
| C148 || 100 µF || 16 V ||
| C148 || 100 µF || 16V || Electrolytic ||
|-
|-
| C149 || 4700 µF || 16 V ||
| C149 || 4700 µF || 16V || Electrolytic ||
|}
|}


=== C103572 Rev 1 (520STFM / 1040STFM final) ===
=== C103572 Rev 1 (1040STFM) ===
 
Final production board. Identical to C103225 but with one additional cap:


<templatestyles src="Template:StyledTable/styles.css" />
<templatestyles src="Template:StyledTable/styles.css" />
{| class="wikitable styled-table"
{| class="wikitable styled-table"
! Ref. !! Value !! Voltage !! Notes
! Ref. Designator !! Capacitance !! Voltage !! Type !! Notes
|-
|-
| C2 || 22 µF || 16 V ||
| C2 || 22 µF || 16V || Electrolytic ||
|-
|-
| C7 || 22 µF || 16 V ||
| C7 || 22 µF || 16V || Electrolytic ||
|-
|-
| C9 || 47 µF || 16 V ||
| C9 || 47 µF || 16V || Electrolytic ||
|-
|-
| C11 || 100 µF || 16 V ||
| C11 || 100 µF || 16V || Electrolytic ||
|-
|-
| C12 || 47 µF || 16 V ||
| C12 || 47 µF || 16V || Electrolytic ||
|-
|-
| C49 || 1000 µF || 16 V ||
| C49 || 1000 µF || 16V || Electrolytic ||
|-
|-
| C70 || 100 µF || 16 V ||
| C70 || 100 µF || 16V || Electrolytic ||
|-
|-
| C73 || 100 µF || 16 V ||
| C73 || 100 µF || 16V || Electrolytic ||
|-
|-
| C74 || 4.7 µF || 35 V || Non-polarised
| C74 || 4.7 µF || 35V || Non-polarised ||
|-
|-
| C75 || 4.7 µF || 35 V ||
| C75 || 4.7 µF || 35V || Electrolytic ||
|-
|-
| C92 || 100 µF || 16 V ||
| C92 || 100 µF || 16V || Electrolytic ||
|-
|-
| C148 || 100 µF || 16 V ||
| C148 || 100 µF || 16V || Electrolytic ||
|-
|-
| C149 || 4700 µF || 16 V ||
| C149 || 4700 µF || 16V || Electrolytic ||
|-
|-
| C190 || 100 µF || 16 V || Additional cap not present on C103225
| C190 || 100 µF || 16V || Electrolytic || Additional cap not present on C103225
|}
|}


== Power Supply Capacitor Lists ==
== PSU 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.
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.


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


=== Mitsumi SR97 / 68-4242A (110–120 V, 1040STF North America) ===
The most common PSU in European 1040STs. Main switching transistor: 2SC2979 (800V, 3A, 40W).<ref name="exxospsu">{{cite web |url=https://www.exxosforum.co.uk/atari/last/psu/index.htm |title=The LaST Upgrade - Atari PSU Repair |publisher=exxos |access-date=2026-03-27}}</ref>


<templatestyles src="Template:StyledTable/styles.css" />
<templatestyles src="Template:StyledTable/styles.css" />
{| class="wikitable styled-table"
{| class="wikitable styled-table"
! Ref. !! Value !! Voltage !! Notes
! Ref. Designator !! Original Value !! Voltage !! Recommended Replacement !! Notes
|-
|-
| C104 || 220 µF || 200 V || Primary side, high voltage
| C104 || 47 µF || 400V || 68 µF 400V || High-voltage primary filter
|-
|-
| C201 || 2200 µF || 16 V || Secondary, +5 V rail
| C201 || 2200 µF || 10V || 4700 µF 16V || Secondary filter
|-
|-
| C202 || 2200 µF || 10 V || Secondary
| C202 || 2200 µF || 16V || 4700 µF 16V || Secondary filter
|-
|-
| C203 || 1000 µF || 16 V || Secondary
| C203 || 2200 µF || 10V || 4700 µF 16V || Secondary filter
|-
|-
| C204 || 2200 µF || 10 V || Secondary
| C204 || 1000 µF || 16V || 1500 µF 16V || Secondary filter
|-
|-
| C205 || 1000 µF || 10 V || Secondary
| C205 || 1000 µF || 10V || 1500 µF 16V || Secondary filter
|-
|-
| C206 || 1 µF || 50 V || Feedback/timing
| C206 || 1 µF || 50V || 1 µF 50V ceramic || Feedback loop; consider ceramic replacement
|}<ref>{{cite web |url=https://wiki.console5.com/wiki/Atari_ST |title=Atari ST – Power Supply Cap Lists |publisher=Console5 TechWiki |access-date=2026-03-27}}</ref>
|}
 
'''Also recommended:''' Replace the bridge rectifier with a KBU1005 (10A, 600V) or similar higher-rated part. The original 2A rectifier is marginal.<ref name="exxospsu"/>


=== Mitsumi SR98 / SR118 / 68-4231A (220–240 V, European 520STFM / 1040STFM) ===
=== Mitsumi SR97 / 68-4242A (110–120V) ===
 
US market PSU.


<templatestyles src="Template:StyledTable/styles.css" />
<templatestyles src="Template:StyledTable/styles.css" />
{| class="wikitable styled-table"
{| class="wikitable styled-table"
! Ref. !! Value !! Voltage !! Notes
! Ref. Designator !! Original Value !! Voltage !! Recommended Replacement !! Notes
|-
|-
| C104 || 47 µF || 400 V || Primary side, high voltage
| C104 || 220 µF || 200V || 220 µF 200V || Primary filter
|-
|-
| C201 || 2200 µF || 10 V || Secondary
| C201 || 2200 µF || 16V || 4700 µF 16V ||
|-
|-
| C202 || 2200 µF || 16 V || Secondary, +5 V rail
| C202 || 2200 µF || 10V || 4700 µF 16V ||
|-
|-
| C203 || 2200 µF || 10 V || Secondary
| C203 || 1000 µF || 16V || 1500 µF 16V ||
|-
|-
| C204 || 1000 µF || 16 V || Secondary
| C204 || 2200 µF || 10V || 4700 µF 16V ||
|-
|-
| C205 || 1000 µF || 10 V || Secondary
| C205 || 1000 µF || 10V || 1500 µF 16V ||
|-
|-
| C206 || 1 µF || 50 V || Feedback/timing
| C206 || 1 µF || 50V || 1 µF 50V ||
|}
|}


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.<ref>{{cite web |url=https://www.exxosforum.co.uk/forum/viewtopic.php?t=25 |title=Atari ST PSU Capacitor & Upgrade Information |publisher=exxos Forum |access-date=2026-03-27}}</ref>
=== ASTEC ASP34 / ASPF34 (220–240V) ===


=== Astec ASP34 / ASPF34-1 (1040STF / 1040STFM) ===
Common European PSU with BU508A main transistor. Multiple sub-revisions (Rev 1–6) exist with minor differences.<ref name="console5"/>


<templatestyles src="Template:StyledTable/styles.css" />
<templatestyles src="Template:StyledTable/styles.css" />
{| class="wikitable styled-table"
{| class="wikitable styled-table"
! Ref. !! Value !! Voltage !! Notes
! Ref. Designator !! Original Value !! Voltage !! Recommended Replacement !! Notes
|-
|-
| C4 || 47 µF || 250 V || Primary side
| C4 || 47 µF || 250V || 47 µF 250V || Primary filter
|-
|-
| C5 || 47 µF || 250 V || Primary side
| C5 || 47 µF || 250V || 47 µF 250V || Primary filter
|-
|-
| C7 || 330 µF || 25 V || (sometimes 35 V original; use 35 V replacements)
| C7 || 330 µF || 25V (or 35V) || 680 µF 35V || Secondary
|-
|-
| C9 || 100 µF || 25 V ||
| C9 || 100 µF || 25V || 100 µF 25V ||
|-
|-
| C12 || 2200 µF || 16 V || Secondary bulk
| C12 || 2200 µF || 16V || 4700 µF 16V ||
|-
|-
| C13 || 4700 µF || 16 V || Secondary bulk, +5 V rail
| C13 || 4700 µF || 16V || 4700 µF 16V ||
|-
|-
| C14 || 330 µF || 25 V || (sometimes 35 V original; use 35 V replacements)
| C14 || 330 µF || 25V (or 35V) || 680 µF 35V ||
|-
|-
| C15 || 330 µF || 25 V || (sometimes 35 V original; use 35 V replacements)
| C15 || 330 µF || 25V (or 35V) || 680 µF 35V ||
|}
|}


=== DVE DSP-508A / DSP-508AA (520STFM / 1040STFM) ===
=== DVE DSP-508A / DSP-508AA (220–240V) ===


'''Note:''' The schematic parts list for this PSU differs from production units. The list below is based on actual production hardware.
Uses BU508A transistor. Generally good regulation even with aged caps.<ref name="exxospsu"/>


<templatestyles src="Template:StyledTable/styles.css" />
<templatestyles src="Template:StyledTable/styles.css" />
{| class="wikitable styled-table"
{| class="wikitable styled-table"
! Ref. !! Value !! Voltage !! Notes
! Ref. Designator !! Original Value !! Voltage !! Recommended Replacement !! Notes
|-
|-
| C3 || 47 µF || 250 V || Primary side
| C3 || 47 µF || 250V || 47 µF 250V || Primary
|-
|-
| C4 || 47 µF || 250 V || Primary side
| C4 || 47 µF || 250V || 47 µF 250V || Primary
|-
|-
| C8 || 330 µF || 25 V ||
| C8 || 330 µF || 25V || 680 µF 25V ||
|-
|-
| C9 || 1 µF || 50 V ||
| C9 || 1 µF || 50V || 1 µF 50V ||
|-
|-
| C?? || 100 µF || 25 V || In shrinkwrap near safety cap at board top
| C?? || 100 µF || 25V || 100 µF 25V || In shrinkwrap near safety cap at board top
|-
|-
| C22 || 2200 µF || 16 V || Secondary bulk
| C20 || 330 µF || 25V || 680 µF 25V ||
|-
|-
| C25 || 2200 µF || 16 V || Secondary bulk
| C22 || 2200 µF || 16V || 4700 µF 16V ||
|-
|-
| C23 || 330 µF || 25 V ||
| C23 || 330 µF || 25V || 680 µF 25V ||
|-
|-
| C20 || 330 µF || 25 V ||
| C25 || 2200 µF || 16V || 4700 µF 16V ||
|}
|}


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


<templatestyles src="Template:StyledTable/styles.css" />
<templatestyles src="Template:StyledTable/styles.css" />
{| class="wikitable styled-table"
{| class="wikitable styled-table"
! Ref. !! Value !! Voltage !! Notes
! Ref. Designator !! Capacitance !! Voltage !! Notes
|-
|-
| C5 || 220 µF || 200 V || Primary side
| C5 || 220 µF || 200V || Primary
|-
|-
| C8 || 47 µF || 16 V ||
| C8 || 47 µF || 16V ||
|-
|-
| C9 || 47 µF || 16 V ||
| C9 || 47 µF || 16V ||
|-
|-
| C101 || 470 µF || 25 V ||
| C101 || 470 µF || 25V ||
|-
|-
| C103 || 100 µF || 25 V ||
| C102 || 470 µF || 25V ||
|-
|-
| C201 || 2200 µF || 10 V || Secondary
| C103 || 100 µF || 25V ||
|-
|-
| C202 || 2200 µF || 10 V || Secondary
| C201 || 2200 µF || 10V ||
|-
|-
| C203 || 470 µF || 10 V ||
| C202 || 2200 µF || 10V ||
|-
|-
| C102 || 470 µF || 25 V ||
| C203 || 470 µF || 10V ||
|-
|-
| C205 || EMPTY || — || Position not populated from factory
| C205 || — || — || Empty position on PCB
|-
|-
| C303 || 1 µF || 50 V ||
| C303 || 1 µF || 50V ||
|}
|}


=== Skynet ATR-1886 (520ST / 1040STF, 120 V North America) ===
=== C070091-014 / Model 1103 (520ST External PSU) ===


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


<templatestyles src="Template:StyledTable/styles.css" />
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{| class="wikitable styled-table"
{| class="wikitable styled-table"
! Value !! Voltage !! Quantity
! Capacitance !! Voltage !! Quantity
|-
|-
| 68 µF || 200 V || 2
| 4700 µF || 16V || 1
|-
|-
| 1000 µF || 25 V || 1
| 2200 µF || 25V || 1
|-
|-
| 1000 µF || 10 V || 1
| 100 µF || 25V || 1
|-
|-
| 330 µF || 25 V || 1
| 220 µF || 25V || 1
|-
|-
| 120 µF || 25 V || 1
| 10 µF || 25V || 1
|-
| 470 µF || 25 V || 2
|}
|}


=== Model 1103 / C070091-014 (Early 520ST, 110 V) ===
== Internal Floppy Drive Capacitors (1040ST) ==


Reference designators are not available for this PSU. Replace by value:
The 1040ST's internal floppy drive (commonly the TDK D357 / T41V) also contains electrolytic capacitors that can fail:


<templatestyles src="Template:StyledTable/styles.css" />
<templatestyles src="Template:StyledTable/styles.css" />
{| class="wikitable styled-table"
{| class="wikitable styled-table"
! Value !! Voltage !! Quantity
! Capacitance !! Voltage !! Quantity !! Notes
|-
|-
| 4700 µF || 16 V || 1
| 22 µF || 16V || 2 ||
|-
|-
| 2200 µF || 25 V || 1
| 47 µF || 16V || 2 ||
|-
|-
| 100 µF || 25 V || 1
| 10 µF || 25V || 1 ||
|-
|-
| 220 µF || 25 V || 1
| 4.7 µF || 35V || 1 ||
|-
|-
| 10 µF || 25 V || 1
| 2.2 µF || 50V || 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.
 
<templatestyles src="Template:StyledTable/styles.css" />
{| class="wikitable styled-table"
! Value !! Voltage !! Quantity !! Notes
|-
| 22 µF || 16 V || 2 ||
|-
| 47 µF || 16 V || 2 ||
|-
|-
| 10 µF || 25 V || 1 ||
| 0.47 µF || 50V || 5 || May be film or ceramic on some drives
|-
|-
| 4.7 µF || 35 V || 1 ||
| 3.3 µF || 50V || 1 ||
|-
| 2.2 µF || 50 V || 1 ||
|-
| 0.47 µF || 50 V || 5 || Film type recommended
|-
| 3.3 µF || 50 V || 1 ||
|}
|}


== Recapping Procedure ==
== Replacement 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) ===
=== General Tips ===


# Identify all electrolytic capacitors on the board and cross-reference with the appropriate cap list above.
# '''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.
# 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).
# '''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.
# 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.
# '''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.<ref name="console5"/>
# Clean the through-holes with the solder sucker or braid until clear.
# '''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.
# Insert the new capacitor, observing correct polarity.
# Solder both legs, using enough solder to form a good concave fillet.
# Trim excess lead length.
# After all capacitors are replaced, clean flux residue with IPA and a brush.


=== Step-by-Step (PSU) ===
=== PSU Recap Procedure (1040ST) ===


'''Mains-side safety:''' The primary-side capacitors (those rated 200 V and above) can retain a lethal charge. Before working on the PSU:
# Unplug the machine and wait at least 5 minutes.
# Remove the top case and disconnect the PSU from the motherboard.
# Remove the PSU from the case (typically held by screws and/or clips).
# Remove the metal PSU shield (if present) — usually held by bent tabs.
# Photograph the PCB before starting, noting all capacitor polarities and positions.
# Desolder each capacitor one at a time, clean the pads, and solder in the replacement.
# '''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.
# Reassemble the PSU shield and reinstall in the case.


# Disconnect from mains.
=== Motherboard Recap Procedure ===
# Switch the power switch to ON and wait 5 minutes to allow capacitors to discharge through internal bleeder resistors.
# 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.
# With the machine open and PSU disconnected, work through each capacitor position.
# Desolder the old cap, clean the pads with desoldering braid, and solder in the replacement.
# 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.
# After completing all replacements, clean the board with IPA to remove flux residue.


== Post-Recap Voltage Verification ==
== Post-Recap Voltage Checks ==


After recapping the PSU, '''always test with a dummy load before connecting to the motherboard:'''
After recapping, verify the following before reconnecting any peripherals:


<templatestyles src="Template:StyledTable/styles.css" />
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{| class="wikitable styled-table"
{| class="wikitable styled-table"
! Test !! Method !! Expected Result
! Test Point !! Expected Value !! Tolerance !! Notes
|-
|-
| +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)
| +5V at motherboard power header || 5.00V || ±0.25V || Measure with machine powered on and under normal load. Adjust PSU trim pot if available.
|-
|-
| +12 V DC || Multimeter across blue wire and black wire, with 10 Ω / 17 W dummy load || 11.0–13.0 V
| +12V at motherboard power header || 12.0V || ±1.0V || Needed for floppy and RS-232.
|-
|-
| +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)
| +5V ripple (oscilloscope) || <200 mV pk-pk || — || Indicates healthy PSU caps. >500 mV indicates a problem remains.
|-
|-
| +12 V ripple || Oscilloscope AC-coupled on +12 V rail, with dummy load || Under 100 mV peak-to-peak
| +5V at CPU VCC pin || 4.90V – 5.10V || — || Check for excessive voltage drop from power header to CPU.
|}
|}


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


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


== Capacitor Upgrade Recommendations ==
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


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.<ref>{{cite web |url=https://www.exxosforum.co.uk/forum/viewtopic.php?t=25 |title=Atari ST PSU Capacitor & Upgrade Information |publisher=exxos Forum |access-date=2026-03-27}}</ref>
When sourcing individual capacitors, use reputable suppliers (Farnell/Element14, Mouser, Digikey, RS Components) to avoid counterfeit or low-quality parts.


When upgrading values:
== Related Pages ==
 
* 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 ==


* [[Atari 520ST]]
* [[Atari 1040ST]]
* [[Atari ST General Maintenance]]
* [[Atari ST General Maintenance]]
* [[Atari ST Troubleshooting Guide]]
* [[Atari ST Troubleshooting Guide]]
* [[Atari 520ST]]
* [[Atari STE Capacitor Replacement Guide]]
* [[Atari 1040ST]]


== References ==
== References ==
<references />
<references/>


{{Navbox-AtariVintageComputers}}
{{Navbox-AtariVintageComputers}}


[[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

[edit | edit source]

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

[edit | edit source]

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

[edit | edit source]
  • 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

[edit | edit source]

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)

[edit | edit source]

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)

[edit | edit source]
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)

[edit | edit source]
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)

[edit | edit source]

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)

[edit | edit source]

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)

[edit | edit source]

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)

[edit | edit source]

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)

[edit | edit source]

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

[edit | edit source]

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)

[edit | edit source]

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)

[edit | edit source]

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)

[edit | edit source]

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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