Editing Atari STE Capacitor Replacement Guide

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The '''Atari STE Capacitor Replacement Guide''' provides complete capacitor lists, board revision identification, and replacement procedures for the '''[[Atari 520STE]]''' and '''[[Atari 1040STE]]'''. Both models share the same motherboard and identical capacitor locations. The only factory difference between the two is installed RAM (520STE: 2× 256 KB SIMMs; 1040STE: 4× 256 KB SIMMs); all capacitor positions, values, and reference designators are the same on both machines.

For general maintenance procedures, see [[Atari STE General Maintenance]]. For fault diagnosis, see [[Atari STE Troubleshooting Guide]].

== Why Recap an STE? ==

The electrolytic capacitors used in Atari STE computers were manufactured in the late 1980s and early 1990s. After 30+ years, these capacitors degrade in several ways:

* '''Increased ESR (Equivalent Series Resistance):''' The capacitor appears functional on a simple capacitance meter but cannot deliver or absorb current quickly enough. This is the most common failure mode in PSU capacitors and causes voltage ripple, random crashes, and video noise.
* '''Reduced capacitance:''' The capacitor drifts below its rated value, reducing filtering effectiveness.
* '''Electrolyte leakage:''' The electrolyte seeps out, potentially corroding nearby traces and pads. Visible as brown or white crystalline residue around the capacitor base.
* '''Short circuit:''' Less common but catastrophic — the capacitor fails short, potentially damaging other components.

PSU capacitors degrade fastest due to thermal stress from the switching power supply. Motherboard capacitors degrade more slowly but are equally important — particularly the DMA audio coupling capacitors (C202, C204, C205, C215) and bulk filter capacitors (C103, C216).

== Before You Begin ==

=== Tools Required ===
* Temperature-controlled soldering iron (recommended 350°C / 660°F for through-hole work)
* Solder wick (desoldering braid) and/or desoldering pump
* 63/37 or 60/40 tin-lead solder (0.8–1.0 mm diameter)
* Flush cutters
* Multimeter with capacitance and ESR measurement capability
* Isopropyl alcohol (99%+) and cotton swabs for flux cleanup
* Anti-static wrist strap
* Pen and paper to record original capacitor orientation before removal

=== Capacitor Selection ===

* '''Use low-ESR, high-ripple-current rated capacitors''' for PSU replacements. Standard-grade electrolytics are insufficient for switch-mode PSU applications and will overheat.
* '''Recommended brands:''' Panasonic FR/FC series, Nichicon HE/UHE series, Rubycon ZLH series. Avoid generic/unbranded capacitors.
* '''Temperature rating:''' 105°C rated capacitors are preferred over 85°C, especially for PSU use.
* '''Voltage rating:''' Match or exceed the original voltage rating. Using a higher voltage rating is acceptable and slightly improves reliability (e.g. replacing 16 V with 25 V).
* '''Non-polarized (NP/bipolar) capacitors:''' Required at positions C202, C204, C205, and C215. These are in the audio signal path and must be non-polarized electrolytics or film capacitors. Do not substitute standard polarized electrolytics.
* '''Physical size:''' Ensure replacements fit the PCB footprint. Modern low-ESR capacitors are often taller than originals at the same capacitance/voltage.

== STE Motherboard Capacitor List ==

The following list applies to all known STE motherboard revisions: '''CA300779-001 REV 5.1''', '''CA401177''', and '''CA4003290'''. Reference designators and values are consistent across all three revisions.<ref>{{cite web |url=https://wiki.console5.com/wiki/Atari_ST |title=Atari ST Cap Lists — STE section |publisher=Console5 TechWiki |access-date=2026-03-27}}</ref><ref>{{cite web |url=https://www.atari-forum.com/viewtopic.php?t=33228 |title=1040 STE capacitors |publisher=Atari-Forum |access-date=2026-03-27}}</ref>

=== Power Section ===

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{| class="wikitable styled-table"
! Ref !! Value !! Voltage !! Type !! Circuit Area !! Notes
|-
| C100 || 10 µF || 35 V || Polarized || Power regulation || 
|-
| C102 || 22 µF || 16 V || Polarized || Power regulation || Some board revisions use 10 µF / 35 V at this position
|-
| C103 || 4700 µF || 16 V || Polarized || +5 V bulk filter || Critical for system stability; replace with low-ESR type
|-
| C107 || 100 µF || 16 V || Polarized || Power filtering ||
|-
| C110 || 100 µF || 16 V || Polarized || Power filtering ||
|}

=== Audio / DMA Sound Section ===

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{| class="wikitable styled-table"
! Ref !! Value !! Voltage !! Type !! Circuit Area !! Notes
|-
| C202 || 4.7 µF || 35 V || '''Non-Polarized''' || DMA sound coupling || '''Critical for DMA audio quality.''' Replace with NP electrolytic or film cap. Degradation causes high-pitched whistle.<ref>{{cite web |url=https://www.atari-forum.com/viewtopic.php?t=24098 |title=STe high pitched whining sound |publisher=Atari-Forum |access-date=2026-03-27}}</ref>
|-
| C204 || 4.7 µF || 35 V || '''Non-Polarized''' || DMA sound coupling || Same as C202 — audio path capacitor
|-
| C205 || 4.7 µF || 35 V || '''Non-Polarized''' || DMA sound coupling || Same as C202 — audio path capacitor
|-
| C215 || 4.7 µF || 35 V || '''Non-Polarized''' || Audio path || Audio coupling
|-
| C216 || 470 µF || 35 V || Polarized || Audio power filter || Large capacitor near audio section
|}

=== Floppy / DMA Controller Section ===

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{| class="wikitable styled-table"
! Ref !! Value !! Voltage !! Type !! Circuit Area !! Notes
|-
| C415 || 470 µF || 16 V || Polarized || Floppy/DMA power filter ||
|-
| C416 || 47 µF || 16 V || Polarized || Floppy section ||
|-
| C417 || 100 µF || 16 V || Polarized || Floppy section ||
|-
| C423 || 100 µF || 16 V || Polarized || DMA controller area ||
|-
| C433 || 1 µF || 50 V || Polarized || DMA section ||
|}

=== CPU / Logic Section ===

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{| class="wikitable styled-table"
! Ref !! Value !! Voltage !! Type !! Circuit Area !! Notes
|-
| C508 || 47 µF || 16 V || Polarized || Logic decoupling ||
|-
| C520 || 47 µF || 16 V || Polarized || Logic decoupling ||
|-
| C525 || 47 µF || 16 V || Polarized || Logic decoupling ||
|-
| C529 || 47 µF || 16 V || Polarized || Logic decoupling ||
|-
| C535 || 47 µF || 16 V || Polarized || Logic decoupling ||
|-
| C537 || 47 µF || 16 V || Polarized || Logic decoupling ||
|-
| C541 || 47 µF || 16 V || Polarized || Logic decoupling ||
|-
| C542 || 10 µF || 35 V || Polarized || Logic section ||
|-
| C543 || 47 µF || 16 V || Polarized || Logic decoupling ||
|-
| C544 || 47 µF || 16 V || Polarized || Logic decoupling ||
|-
| C546 || 47 µF || 16 V || Polarized || Logic decoupling ||
|-
| C547 || 47 µF || 16 V || Polarized || Logic decoupling ||
|}

=== Video / Output Section ===

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{| class="wikitable styled-table"
! Ref !! Value !! Voltage !! Type !! Circuit Area !! Notes
|-
| C558 || 100 µF || 16 V || Polarized || Video/output filtering ||
|-
| C561 || 100 µF || 16 V || Polarized || Video/output filtering ||
|-
| C564 || 100 µF || 16 V || Polarized || Video/output filtering ||
|-
| C566 || 47 µF || 16 V || Polarized || Video section ||
|-
| C567 || 47 µF || 16 V || Polarized || Video section ||
|-
| C600 || 100 µF || 16 V || Polarized || Output section ||
|}

=== Summary Count (Motherboard) ===

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{| class="wikitable styled-table"
! Value !! Voltage !! Type !! Quantity
|-
| 4700 µF || 16 V || Polarized || 1
|-
| 470 µF || 35 V || Polarized || 1
|-
| 470 µF || 16 V || Polarized || 1
|-
| 100 µF || 16 V || Polarized || 7
|-
| 47 µF || 16 V || Polarized || 12
|-
| 22 µF || 16 V || Polarized || 1
|-
| 10 µF || 35 V || Polarized || 2
|-
| 4.7 µF || 35 V || Non-Polarized || 4
|-
| 1 µF || 50 V || Polarized || 1
|-
| colspan="3" | '''Total''' || '''30'''
|}

== PSU Capacitor Lists ==

The STE uses the same internal PSU types as the later STFM models. Identify your PSU by the model number printed on the PSU PCB.

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

The most common PSU in European STE machines.<ref>{{cite web |url=https://wiki.console5.com/wiki/Atari_ST |title=Atari ST Cap Lists — Mitsumi SR98 |publisher=Console5 TechWiki |access-date=2026-03-27}}</ref><ref>{{cite web |url=https://www.exxosforum.co.uk/atari/last/psu/index.htm |title=The LaST Upgrade — SR98 repair |publisher=exxos |access-date=2026-03-27}}</ref>

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{| class="wikitable styled-table"
! Ref !! Value !! Voltage !! Notes
|-
| C104 || 47 µF || 400 V || Primary filter — '''HIGH VOLTAGE'''. Replace with 68 µF 400 V for improved filtering.
|-
| C201 || 2200 µF || 10 V || Secondary output filter. Replace with 4700 µF 16 V for improved performance.
|-
| C202 || 2200 µF || 16 V || Secondary output filter. Replace with 4700 µF 16 V.
|-
| C203 || 2200 µF || 10 V || Secondary output filter. Replace with 4700 µF 16 V.
|-
| C204 || 1000 µF || 16 V || Secondary output filter. Replace with 1500 µF 16 V.
|-
| C205 || 1000 µF || 10 V || Secondary output filter. Replace with 1500 µF 16 V.
|-
| C206 || 1 µF || 50 V || Feedback/compensation capacitor.
|}

'''Additional SR98 modifications:'''
* Replace the 2A bridge rectifier with a KBU1005 (10 A, 600 V) for improved reliability and lower voltage drop.
* Replace the output diode (HRW34) with an STPS10H100CFP Schottky type for reduced ripple (500 mV → 200 mV measured improvement) and lower heatsink temperature (49°C → 39°C).
* For improved peak current response (reduces video dimming during floppy access): replace R202 with 1 kΩ and R201 with 1.2 kΩ, then readjust the trimmer pot to 5.00 V on the +5 V rail.<ref>{{cite web |url=https://www.exxosforum.co.uk/atari/last/psu/index.htm |title=The LaST Upgrade — SR98 peak current update |publisher=exxos |access-date=2026-03-27}}</ref>

=== DVE DSP-508A / DSP-508AA ===

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{| class="wikitable styled-table"
! Ref !! Value !! Voltage !! Notes
|-
| C3 || 47 µF || 250 V || Primary filter — '''HIGH VOLTAGE'''
|-
| C4 || 47 µF || 250 V || Primary filter — '''HIGH VOLTAGE'''
|-
| C8 || 330 µF || 25 V || Secondary filter. Replace with 680 µF 25 V.
|-
| C9 || 1 µF || 50 V || Compensation.
|-
| C?? || 100 µF || 25 V || In shrinkwrap near safety cap at board top.
|-
| C22 || 2200 µF || 16 V || Secondary output. Replace with 4700 µF 16 V.
|-
| C25 || 2200 µF || 16 V || Secondary output. Replace with 4700 µF 16 V.
|-
| C23 || 330 µF || 25 V || Secondary filter. Replace with 680 µF 25 V.
|-
| C20 || 330 µF || 25 V || Secondary filter. Replace with 680 µF 25 V.
|}

The DVE PSU uses a BU508A switching transistor, which has superior voltage and current ratings compared to the SR98's 2SC2979. This PSU generally has better regulation and is considered one of the more robust STE PSU designs. Replace the bridge rectifier with a KBU1005 (10 A, 600 V) as with the SR98.<ref>{{cite web |url=https://www.exxosforum.co.uk/atari/last/psu/index.htm |title=The LaST Upgrade — DVE DSP-508A |publisher=exxos |access-date=2026-03-27}}</ref>

=== ASTEC ASP34 / ASPF34 ===

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{| class="wikitable styled-table"
! Ref !! Value !! Voltage !! Notes
|-
| C4 || 47 µF || 250 V || Primary filter — '''HIGH VOLTAGE'''. Replace with 47–68 µF 250 V.
|-
| C5 || 47 µF || 250 V || Primary filter — '''HIGH VOLTAGE'''. Replace with 47–68 µF 250 V.
|-
| C7 || 330 µF || 25–35 V || Secondary filter. Replace with 470–820 µF 35 V.
|-
| C9 || 100 µF || 25 V || Secondary filter.
|-
| C14 || 330 µF || 25–35 V || Secondary filter. Replace with 470–820 µF 35 V.
|-
| C15 || 330 µF || 25–35 V || Secondary filter. Replace with 470–820 µF 35 V.
|-
| C13 || 4700 µF || 16 V || Main +5 V filter.
|-
| C12 || 2200 µF || 16 V || Secondary filter. Replace with 4700 µF 16 V.
|}

Uses BU508 switching transistor. Re-solder the transistor legs and any other components on the heatsink as a preventive measure.<ref>{{cite web |url=https://www.exxosforum.co.uk/atari/last/psu/index.htm |title=The LaST Upgrade — ASP34 |publisher=exxos |access-date=2026-03-27}}</ref>

== Board Revision Identification ==

Identify your STE motherboard revision by the part number silkscreened on the PCB, typically in a corner near the edge connectors.

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{| class="wikitable styled-table"
! Board Number !! Key Characteristics !! Cap List Differences
|-
| CA300779-001 REV 5.1 || Early production STE board. Separate BLiTTER chip (PLCC-68). GST Shifter in DIP-64 socket (C300588). DIP-64 or PLCC-68 CPU. || Standard cap list as above. C102 may be 10 µF / 35 V instead of 22 µF / 16 V.
|-
| CA401177 || Mid-production board. Some units have surface-mounted MC68000 CPU. || Standard cap list. No known capacitor value differences.
|-
| CA4003290 || Later/final production STE board. Most commonly encountered. Used in both 520STE and 1040STE. || Standard cap list. No known capacitor value differences.
|}

'''Note:''' Despite different board numbers, all three STE motherboard revisions use the same capacitor reference designators and values. The Console5 cap kit "Atari 520STE/1040STE Computer Cap Kit (Main STE PCB)" covers all revisions.<ref>{{cite web |url=https://console5.com/store/atari-520ste-1040ste-computer-cap-kit-main-ste-pcb.html |title=Atari 520STE/1040STE Cap Kit |publisher=Console5 |access-date=2026-03-27}}</ref>

== Replacement Procedure ==

=== Motherboard Recap ===

# '''Photograph the motherboard''' before starting. Record the polarity orientation of each capacitor — the negative (−) stripe on the capacitor body should match the marking on the PCB silkscreen. For non-polarized capacitors (C202, C204, C205, C215), orientation does not matter.
# '''Remove the old capacitor:''' Heat one lead while gently pulling the capacitor away from the board. When one lead is free, heat the other. Alternatively, cut the capacitor body away and remove each lead individually.
# '''Clean the through-hole pad:''' Apply solder wick to remove old solder from both holes. The holes should be clear enough to pass a new component lead through. If a pad lifts, it can be repaired with a small wire jumper soldered to the nearest trace.
# '''Install the new capacitor:''' Insert leads through the PCB holes, observing polarity markings. The longer lead is positive (+). Solder both leads. Trim excess leads flush with the solder joint.
# '''Inspect each joint:''' A good joint is shiny and concave. Re-flow any dull, blobby, or cold-looking joints.
# '''Clean flux residue''' with IPA and a brush after completing all replacements.

=== PSU Recap ===

'''WARNING: PSU primary-side capacitors (C104, C3, C4, C5 depending on model) are rated at 250–400 V. Ensure all capacitors are fully discharged before working on the PSU. Discharge through a 10 kΩ 2 W resistor held across the capacitor terminals, not by shorting.'''

# Follow the same removal and installation procedure as the motherboard.
# '''Take extra care with high-voltage primary capacitors.''' These have higher lead spacing and require capacitors rated for high ripple current.
# '''Re-solder the main switching transistor legs''' (BU508 or 2SC2979) while the PSU is open.
# '''Re-solder the bridge rectifier terminals.'''
# '''Consider upgrading the bridge rectifier''' to a KBU1005 (10 A, 600 V) on all PSU models. The original 2 A rectifiers are marginal.

== Post-Recap Voltage Checks ==

After completing the recap, reconnect the PSU to the motherboard and power on. Verify the following voltages:

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{| class="wikitable styled-table"
! Rail !! Expected !! Acceptable Range !! Measurement Point !! Action if Out of Range
|-
| +5 V || 5.00 V || 4.75–5.25 V || Across C103 (4700 µF); joystick port pin 7 to ground || Adjust PSU trim pot. If no trim pot or unable to adjust, PSU may need further repair.
|-
| +12 V || 12.00 V || 11.40–12.60 V || Floppy drive power connector +12 V pin || Trim pot adjustment (if available). Some PSUs regulate only +5 V; +12 V is semi-regulated.
|-
| −12 V || −12.00 V || −10.80 to −13.20 V || MC1489 pin 14 || Derived from +12 V via inverter circuit. If absent, check inverter components.
|}

'''Ripple check (oscilloscope):''' Measure AC ripple on the +5 V rail at C103. Expected results after a proper recap:
* '''Mitsumi SR98:''' ≤400 mV (≤200 mV with output diode upgrade to Schottky type)
* '''DVE DSP-508A:''' ≤200 mV (excellent regulation)
* '''ASTEC ASP34:''' ≤500 mV

If ripple exceeds these values after recap, check for a failed opto-coupler, incorrect capacitor values, or a failing switching transistor.

== DMA Audio Verification ==

After replacing the audio-path capacitors (C202, C204, C205, C215, C216), verify DMA sound quality:

# Boot the STE to the GEM desktop.
# Run a DMA sound test program (e.g. fenarinarsa's ste_dmatest from https://github.com/fenarinarsa/ste_dmatest/releases/).
# Listen for:
#* Clean playback without high-pitched whistles (confirms C202/C204/C205 replacement was successful).
#* No crackling or popping (if present, see DAC latch fixes in [[Atari STE Troubleshooting Guide]]).
#* Balanced stereo output on both RCA channels.
# Test Microwire volume control by adjusting master volume — the LMC1992 should respond smoothly.

== Capacitor Kit Sources ==

* '''Console5:''' https://console5.com/store/atari-520ste-1040ste-computer-cap-kit-main-ste-pcb.html (motherboard kit)
* '''Console5 PSU kits:''' Available for Mitsumi SR98, DVE DSP-508A, and ASTEC ASP34 models
* '''exxos:''' https://www.exxosforum.co.uk/atari/store2/ (PSU recap kits and replacement PSUs)
* '''Centurion Tech:''' https://centuriontech.eu/product/1040ste-recap-set/ (motherboard recap sets)

== See Also ==
* [[Atari 520STE]]
* [[Atari 1040STE]]
* [[Atari STE General Maintenance]]
* [[Atari STE Troubleshooting Guide]]

== References ==
<references />

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[[Category:Atari Capacitor Replacement Guides]]