Atari ST PSU. Internal PSU replacement for Atari ST & MegaST
  • Atari ST PSU. Internal PSU replacement for Atari ST & MegaST
  • Atari ST PSU. Internal PSU replacement for Atari ST & MegaST
  • Atari ST PSU. Internal PSU replacement for Atari ST & MegaST
  • Atari ST PSU. Internal PSU replacement for Atari ST & MegaST
  • Atari ST PSU. Internal PSU replacement for Atari ST & MegaST
  • Atari ST PSU. Internal PSU replacement for Atari ST & MegaST
  • Atari ST PSU. Internal PSU replacement for Atari ST & MegaST
  • Atari ST PSU. Internal PSU replacement for Atari ST & MegaST
  • Atari ST PSU. Internal PSU replacement for Atari ST & MegaST

ATARI ST & MegaST Internal PSU

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ATARI ST PSU. An internal power supply for all ATARI STF/FM/E & MegaST computers

An internal Atari ST PSU - modern replacement power supply unit for Atari 520, 1040 STF/FM/E & Atari MegaST computers using an internal power supply. 50W of power - nearly two times stronger than original and capable to deliver up to 5A @ 5VDC and 2A @ 12VDC rail. By default equipped with famous Electroware's over voltage protection (OVP) and 5VDC output voltage fine tuning to set exact 5VDC for your particular ATARI ST system. Electroware PSU is always the one and only absolute industry standard followed by many copiers & clones you should beware!

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Atari ST internal PSU by Electroware: new internals for your Atari 520/1040 or MegaST computer. Efficient & reliable 50W PSU to power & preserve! Replacing the original Mitsumi/Phihong power supply units and offering peace of mind as it's always equipped with Electroware's OVP circuits and easy to replace fuses. Output voltage fine tuning, additional ripple filtering and two auxiliary universal power outputs by default!

Stay original! Buy only the genuine Electroware's gear and beware the fancy overrated clones flooding eBay & WWW!



Atari ST and MegaST internal PSU by Electroware.

Atari ST internal PSU before installation.

Atari ST computers were equipped with good quality, switched mode internal PSU (like the Mitsumi brand ~30W one planted in my 1040STFM see photos). It can be re-capped, repaired or refurbished to last longer... but even then you can't be sure as 35 years old electronics may fail anytime (MTBF expired). I saw many of ST's offered without PSU or with dead PSU in overall unknown main board state... you can't be sure what chips are still alive after the PSU fails. If your ATARI PSU is gone, not longer working, or you are not sure about it's condition - it's time to get a solid, superior quality replacement, especially if your Atari ST is using many modern enchantments as fans and users are creating wonderful hardware stuff like UltraSatan FDD emulators (using SD Card), HDD drives or CF card, video output enhancers, VGA/HDMI RasPi adapters, WiFi serial modems, memory upgrades, accelerators etc... all to enjoy.  But remember that all of these gadgets are stressing the PSU and original one become even more dangerous when working overloaded.

OK, let's go and replace the PSU: I've searched the competitor's offer and found that some rare units seems quite reliable but are assembled in low volume, most unavailable actually and even if in stock, are offered in extremely high price as for the overall computer worth. Cheaper constructions are available, like the one based on cheap CUI PSK-20D-5 / CUI PSK-20-12 bricks, but are not very convincing with their 150mVp-p ripple level, offering no real over voltage protection (it's activated at ~7VDC long time after your ST chips will gone with the smoke) and no voltage tuning at all. Is there really no way out?

LED protection module add-on board for Atari 520ST & Atari 260ST

LED protection module add-on board for Atari 520ST & Atari 260ST

No. I decided to make a new PSU: as usual the compromise blend of price, quality and features. Based on our experiences with successful and well-known Amiga and Atari 520ST external PSU models. It's 5A@5VDC and 2A@12VDC giving 50W of total power (54W in short term peak). Ripple at reasonable 80mVp-p level. By default equipped with our famous over voltage protections for both 5V and 12V rails, 5VDC voltage tuning in safe range of 5-5.5VDC (to feed your accelerated machines stuffed with add-ons), easy to replace fuses and two universal connectors (5VD & 12 VDC) to supply fans, HDD or any other internal/external devices (even an external SF-314/SF-354 FDDs with some special-made cable).

This new PSU is compatible with most of Atari ST computers using an internal power supply (520 or 1040 STF/FM/E models & Atari MegaST). To save costs we are utilizing the original mounting plates, runners, covering shields, AC connector and power switch (these parts needs to be extracted from your ST). Notice that some basic electric knowledge and tools are needed to replace the PSU the safe way and most of all - you are working with high AC voltage - so to avoid electric shock, always operate with main AC cable unplugged and do not turn it on when not fully mounted, double-checked and covered with all shields!


Atari 520ST and SF314 PSU "2in1"

Atari 520ST PSU and SF314 PSU - original and new comparison.


  • ATARI Atari 520, 1040 STF/FM/E & Atari MegaST compatible 
  • Stabilized & filtered 5VDC up to 5A output (5.5A peak)  
  • Stabilized & filtered 12VDC up to 2A output (2.2 peak)
  • Active & passive over voltage protection for both 5VDC and 12VDC rails
  • Voltage spikes suppression with ultra-fast TVS diode
  • Over current protection for all output lines
  • Trimmer for 5VDC voltage fine tuning in safe, limited range protected by OVP
  • Fully isolated & fused on AC and DC side. 
  • Easy to replace popular 5x20mm fuses
  • Two auxiliary universal power ports for 5VDC and 12VDC devices.
  • Universal AC input range 100-250VAC (can run in both USA and Europe).
  • Power good status LEDs for 5VDC and 12VDC voltages.
  • Additional output ripple reduction by low-ESR capacitor filtering (nominal ripple 80mVp-p)
  • 100% repairable, easy to disassemble by qualified technician, spare parts available.
  • Safety standards: UL60950-1, TUV EN60950-1, ANSI/AAMI ES60601-1, TUV EN60601-1, IEC60601-1
  • All electric cables terminated with the industrial grade, detachable wire-to-board connectors. There's no amateur and dangerous direct AC and DC wire-to-board soldering!


Atari 520ST & 260ST PSU status LED indicator

Atari ST520 & SF314 "2in1" PSU power switch. Detachable AC input cable


Always work with AC cable unplugged and connect it only after fitting all the shields and covers back to their original place!

Always connect the ground wire (with the screw to the metal shield)!

I suggest to desolder the old AC_L and AC_N wires from the original PSU PCB - instead of cutting them, but if there is no other way - cut as close to the PCB as possible and tin the cable endings to prevent oxidation or at least twist the wire's copper strings together to bind them firmly and avoid short circuits. New AC terminal connector requires no soldering when connecting the original AC_L and AC_N copper wires as shown on photos. Anyway depending on your original Atari PSU assembly the AC cables may came out a bit short, especially AC_L (black one). Don't worry, in such case use our AC extension cable with Wago fastener (provided with every PSU unit). I suggest to protect the AC L and N wires connection once mounted to the terminal and fix them additionally with plastic ZIP (provided).



Every single Electroware PSU unit is triple tested before dispatch. To assure flawless quality and long lasting performance we are testing with original Atari gear from our collection as well as by burn-in test with customized load simulating devices causing 150% overload comparing to regular ATARI ST or MegaST computer system.

Stay with the original Electroware products to gain top build quality, unique features unavailable with the clone products.

By purchasing this product you are supporting the retro computing community and contributing to our continuous developing process. Thank you!



Disconnect the main AC power cord to install/uninstall the internal PSU inits. Always use ground connection and the full set of shields and protection covers to avoid the electric shock. Please wait at least hour to discharge the AC capacitors before attempting to disassemble!

Risk of electrical shock and energy hazard when working. All failures should be examined by a qualified technicians only. Risk of fire or electrical shock. The ventilation holes should be protected from foreign objects or dripping liquids. Please do not install power supplies in places with high ambient temperature or close to the heat source. Enclosed power supplies are intent to work in indoor locations, it's not allowed to use power supplies outdoor, in dust or high moisture. Output current and output wattage must not exceed the rated values.

This replacement Atari ST PSU has been designed for Atari 520ST & 260ST vintage computer systems using ATARI ST or ATARI MegaST only and should be considered as an component of Atari ST computer system. Do not connect to any other devices as it's not a general purpose PSU. Manufacturer is not responsible for any consequences of unauthorized or arbitrary repairs, modifications or incorrect usage. Please notice that new, properly working replacement Atari ST PSU is reducing the system's potential fail rate but still is not guaranteeing that entire Atari ST system will work correctly (it's 40 years old).



Stay original! Buy only the genuine gear and beware the fancy overrated clones flooding eBay & WWW!


Specific References