ATARI ST & MegaST Internal PSU

Atari ST internal PSU by Electroware: fresh internals for your Atari 520/1040 or Mega ST.

An efficient & reliable 50 W replacement power supply to power & preserve. Drop-in alternative to the original Mitsumi/Phihong units, with Electroware OVP, user-replaceable fuses, 5 V fine trim, added ripple filtering and two auxiliary 5 V/12 V headers as standard.

Stay original! Choose genuine Electroware and beware of clones flooding eBay & the web.

ATARI ST internal PSU: NEW LIFE FROM WITHIN.

Atari ST computers shipped with decent switched-mode internal PSUs (e.g., ~30 W Mitsumi in many 1040STFM units). Recapping can extend life, but after ~35 years even repaired boards can fail without warning. We often see STs sold with missing or dead PSUs and unknown board condition—once a PSU goes out of spec, custom chips may already be at risk. If your supply is unstable, missing, or simply untrusted, a modern, safe replacement is the sensible path—especially if you run today’s enhancements: UltraSatan/SD HDD, CF/IDE, video boosters, VGA/HDMI adapters, Wi-Fi serial, RAM/CPU accelerators, internal fans, etc. These upgrades raise current demand and make tired originals a liability.

We evaluated alternatives. Some boutique units are solid but scarce and costly. Cheaper designs (e.g., based on low-cost 20 W bricks) can have high ripple (~150 mVp-p), lack meaningful OVP (often triggering far above 5 V, too late to save chips) and offer no voltage trim. That wasn’t good enough for daily use—or preservation.

So we built our own: a balanced design for price, quality and features, drawing on our Amiga and Atari 520ST external PSU lines. It delivers 5 A @ 5 V and 2 A @ 12 V (50 W continuous; short peaks to ~54 W). Typical ripple is ~80 mVp-p. Standard protections cover both rails (OVP, OCP), plus an adjustable 5.00 V trim (safe, limited range) for accelerated, add-on-heavy builds. You also get easy 5×20 mm fuses and two aux power headers (5 V/12 V) for fans, HDD/CF/SD devices or even external SF-314/SF-354 via a suitable cable.

Compatibility: most Atari ST models with internal PSU (520/1040 STF/STFM/STE and Mega ST). To control cost and keep the original look, you re-use factory mounting plates, runners, shields, AC inlet and power switch (remove these from your unit). Safety first: mains AC is dangerous—work only with the cord unplugged, and restore all shields before power-up. Basic electrical skills and proper tools are required.

UNIQUE FEATURES & QUALITY

• Compatible with Atari 520/1040 STF/STFM/STE & Mega ST
• Stabilized, filtered 5 VDC up to 5 A (5.5 A peak)
• Stabilized, filtered 12 VDC up to 2 A (2.2 A peak)
• Active & passive OVP on 5 V and 12 V rails
• Fast TVS diode suppression for voltage spikes
• OCP (over-current protection) on all outputs
• Protected 5 V trimmer for precise, safe fine-tuning
• Fully isolated & fused on AC and DC sides
• Standard, easy-to-replace 5×20 mm fuses
• Two auxiliary power headers: 5 VDC and 12 VDC
• Universal AC input 100–250 VAC (EU/US compatible)
• “Power good” status LEDs for 5 V/12 V
• Extra ripple reduction via low-ESR capacitors (typ. ~80 mVp-p)
• 100% repairable; spare parts available; serviceable construction
• Industrial, detachable wire-to-board connectors—no unsafe direct soldered mains/DC leads

INSTALLATION TIPS

Always work with the AC cord unplugged. Refit all shields and covers before connecting mains power.

Always connect the ground wire securely to the metal shield.

If possible, desolder the original AC_L/AC_N from the old PSU PCB rather than cutting. If you must cut, do it close to the PCB and tin the wire ends (or at least twist firmly). The new AC terminal accepts the original copper leads—no soldering required. If your AC wires are short (often AC_L), use the supplied AC extension with Wago fastener. After mounting, secure AC leads at the terminal and add the provided zip tie as strain relief.

TRUST & RESPONSIBILITY

Every Electroware PSU is triple-tested before dispatch. We verify with original Atari hardware from our collection and perform burn-in against custom loads up to ~150% of a typical ST/Mega ST system to validate thermal and protection margins.

Staying with genuine Electroware ensures build quality and features that clones don’t match.

By choosing this PSU you support the retro community and ongoing development—thank you.

Warning!

Disconnect mains power before any work. Always use the ground connection and restore all shields/covers to avoid electric shock. Allow at least one hour for capacitors to discharge before disassembly.

Risk of electric shock and energy hazard. Service should be performed by qualified technicians only. Protect ventilation openings from foreign objects and moisture. Do not install near heat sources or in high-temperature, dusty or damp locations. For indoor use only. Do not exceed rated output current or wattage.

This replacement PSU is designed as a component for Atari ST / Mega ST vintage systems only—do not use with other devices. The manufacturer is not responsible for damage from unauthorized repairs, modifications or misuse. A new PSU reduces failure risk but cannot guarantee overall system health in 40-year-old hardware.

Stay original! Choose genuine C64PSU.com gear and beware of overrated clones.