Atari Mega STE Capacitor Replacement Guide

This article provides a complete capacitor replacement (recapping) guide for the Atari Mega STE computer, covering the Phihong PSM-5341 power supply unit and the motherboard. The Phihong PSU is shared with the Atari TT030 — TT030 owners should reference this guide as well.

When to recap

Recapping is recommended when any of the following are observed:

• Video noise, flickering, or screen dimming during floppy or hard disk access
• Random crashes or instability (especially at 16 MHz)
• PSU emitting ticking, whining, or buzzing sounds
• Visible electrolyte leakage or capacitor bulging
• Weak or wavering display output
• The machine is approaching or exceeding 30 years of age (preventive maintenance)

Tools and materials

• Temperature-controlled soldering station
• Solder wick and/or desoldering pump (or dedicated desoldering iron — the Duratool D01849 40W desoldering iron is effective for this work)
• High-quality replacement electrolytic capacitors (Panasonic FR-series recommended for low ESR and long life)
• Isopropyl alcohol (99%+) and lint-free swabs
• Digital multimeter with capacitance measurement
• Flux (no-clean type)
• Dummy load resistors for PSU testing: 2.2Ω 17W (for +5V rail) and 10Ω 17W (for +12V rail)

Power supply capacitor list — Phihong PSM-5341

The Phihong PSM-5341 is a universal voltage PSU (100–240 VAC input). It is used in both the Mega STE and the TT030. A pre-assembled capacitor kit is available from Console5 and from exxos.

Original values

Designator	Original capacitance	Original voltage	Notes
C6	120 µF	400V	Primary filter — high voltage, exercise extreme caution
C7	10 µF	400V	Primary side — high voltage
C8	100 µF	25V
C13	4,700 µF	16V	Main +5V rail bulk capacitor
C14	2,200 µF	10V	Secondary filter
C15	1,000 µF	16V
C16	1,000 µF	16V
C17	680 µF	16V
C18	680 µF	16V
C19	100 µF	10V
C20	3.3 µF	50V
C23	22 µF	25V
C24	220 µF	25V
C26	4.7 µF	50V

Total: 14 electrolytic capacitors in PSU.

Recommended replacement values (exxos specifications)

The following replacement values are based on the exxos upgrade specifications, which increase capacitance on critical rails for improved regulation and peak current handling:

Designator	Replacement capacitance	Replacement voltage	Part example
C6	120 µF	400V	Rubycon BXW 400BXW120MEFR18X30
C7	10 µF	450V	Panasonic EE-series EEUEE2W100
C8	220 µF	50V	Panasonic FR-series EEUFR1H221B
C13	4,700 µF	16V	Panasonic FR-series EEUFR1C472B
C14	4,700 µF	16V	Panasonic FR-series EEUFR1C472B
C15	1,500 µF	16V	Panasonic FR-series EEUFR1C152B
C16	1,500 µF	16V	Panasonic FR-series EEUFR1C152B
C17	1,500 µF	16V	Panasonic FR-series EEUFR1C152B
C18	1,500 µF	16V	Panasonic FR-series EEUFR1C152B
C19	100 µF	16V	Panasonic FR-series EEUFR1C101B
C20	10 µF	50V	Panasonic FR-series EEUFR1H100
C23	10 µF	50V	Panasonic FR-series EEUFR1H100
C24	220 µF	50V	Panasonic FR-series EEUFR1H221B
C26	10 µF	50V	Panasonic FR-series EEUFR1H100

Physical dimensions

When sourcing capacitors, verify that replacement parts fit the PCB footprint. Key dimensions to check:

• Diameter — Must not exceed the pad spacing on the PCB.
• Height — Must clear the PSU housing when reassembled.
• Lead spacing — Must match the PCB hole spacing. Some positions may need leads bent slightly to fit.

C6 (120 µF 400V) is the largest capacitor and requires careful dimensional matching. Typical dimensions: 18 mm diameter × 30 mm height with 17.5 mm lead spacing.

Motherboard capacitor list

The Mega STE motherboard uses STE-derived circuitry. The motherboard contains fewer electrolytic capacitors than the STE mainboard, as some decoupling functions are handled by the PSU's improved filtering. The exact capacitor count varies slightly by board revision.

The Mega STE motherboard shares the same basic STE capacitor configuration. The following is based on documented board examination:

Key motherboard electrolytic capacitors include:

Designator	Capacitance	Voltage	Notes
C100	10 µF	35V
C102	22 µF	16V	May be 10 µF / 35V on some revisions
C103	4,700 µF	16V	Main bulk decoupling
C107	100 µF	16V
C110	100 µF	16V
C202	4.7 µF	35V	Non-polarised (NP/bipolar) — audio circuit
C204	4.7 µF	35V	Non-polarised — audio circuit
C205	4.7 µF	35V	Non-polarised — audio circuit
C215	4.7 µF	35V	Non-polarised — audio circuit
C216	470 µF	35V
C415	470 µF	16V
C416	47 µF	16V
C417	100 µF	16V
C423	100 µF	16V
C433	1 µF	50V

Note: This list is based on the STE-compatible PCB layout used in the Mega STE. Board revisions may differ slightly. Always verify capacitor values against the actual components fitted to your specific board before ordering replacements. Photograph and document each capacitor position before removal.

Audio circuit capacitors

The four non-polarised (NP/bipolar) capacitors (C202, C204, C205, C215) are in the DMA stereo audio path. These must be replaced with non-polarised types. Using standard polarised electrolytic capacitors in these positions will cause audio distortion or damage. Film capacitors can be used as replacements if non-polarised electrolytics are unavailable.

PSU recapping procedure

Preparation

1. Disconnect the PSU from the computer and mains. Remove the PSU from the Mega STE case — take care not to knock nearby components.
2. Discharge period — Leave the PSU disconnected for at least 24 hours to allow capacitors to discharge.
3. Verify discharge — With a multimeter set to DC voltage, check across C6 and C7 terminals. Any reading above 1V indicates residual charge.

Removal and replacement

1. Disassemble the PSU: remove the metal housing screws, carefully remove the top cover, then remove PCB mounting screws.
2. Document all capacitor positions, values, and polarities. Sketch or photograph the board from both sides.
3. Desolder each capacitor. Use a desoldering iron or combination of solder wick and pump.
4. Clean pads with IPA and inspect for lifted traces or damaged plating.
5. Install new capacitors, verifying polarity for each. Reversed polarity on the 400V capacitors (C6, C7) can cause violent explosion.
6. Double-check all polarities before soldering.
7. Inspect all solder joints. Ensure no bridges, cold joints, or insufficient solder.
8. Reassemble the PSU housing.

Independent PSU testing

Before reconnecting to the computer, test the PSU independently:

1. Attach dummy load resistors: 2.2Ω 17W between +5V (red) and GND (black); 10Ω 17W between +12V (yellow) and GND (black).
2. Power on using a switched power strip for safety (allows rapid power-off).
3. Do not run for more than 30 seconds — the dummy load resistors will overheat.
4. Measure all output voltages:

• • +5V (red): 4.95–5.10V
  • +12V (yellow): 11.8–12.2V
  • -12V (blue): -11.8 to -12.2V
  • -5V (white): -4.90 to -5.10V
  • PG (orange): ~+5V

1. Power off. If all voltages are within specification, the PSU can be reconnected to the computer.

Motherboard recapping procedure

1. Remove the motherboard from the case.
2. Photograph all capacitor positions and polarities.
3. Desolder each electrolytic capacitor carefully. C103 (4,700 µF) is a large part requiring extended heating time.
4. Clean pads.
5. Install replacements. For NP positions (C202, C204, C205, C215), use non-polarised capacitors only.
6. Inspect all joints.
7. Reassemble and test.

Post-recap verification

After recapping both PSU and motherboard:

1. PSU voltages — Verify all rails within specification.
2. Cold boot — System should boot cleanly to GEM desktop.
3. 16 MHz + cache test — Enable 16 MHz and cache via GENERAL.CPX. Run for an extended period to verify stability.
4. Video quality — Display should be stable with no noise, ghosting, or dimming.
5. Floppy operation — Read and write a known-good disk.
6. SCSI hard disk — If fitted, verify reliable operation.
7. DMA audio — Test stereo output from RCA jacks with a sample player or tracker.
8. Compare output voltages with pre-recap measurements to quantify improvement.

Capacitor sourcing

Pre-assembled kits:

• Console5 — console5.com (PSU kit for Phihong PSM-5341)
• exxos — exxosforum.co.uk/atari/store2/ (PSU recap kits with upgraded values)
• RetroPassion — retropassion.co.uk (Mega STE PSU recapping service)

Individual components:

• Mouser Electronics — mouser.com
• Farnell/element14 — farnell.com
• Digi-Key — digikey.com

Recommended brands: Panasonic (FR-series), Nichicon, Rubycon. Avoid unbranded capacitors from online marketplaces.

See also

• Atari Mega STE
• Atari Mega STE General Maintenance
• Atari Mega STE Troubleshooting Guide