Modifying a Cisco PSU for Amiga

Parts and tools needed:

  • Astec AA22340 Power Supply
  • Faulty Amiga power supply with cable intact
  • Soldering iron
  • Multimeter
  • Crimp eyelet connector and pliers / crimp tool

The power brick for your Amiga 500, 600 or 1200 does an important job, but it’s getting on a bit now with many being well over 30 years old. Thankfully they don’t tend to fail in a dangerous state, like the Commodore 64 units do, but they can still potentially damage your Amiga or cause instability as the voltages vary from the design specs.

Many guides exist to put a Mean Well power supply inside the original plastic case, and this is a really good idea – they’re high quality switch mode power supplies designed for reliability, and in fact pre-built power supplies exist based around these such as the Keelog models which feature a Mean Well RPT50B in a custom case. The RT65B is a higher power unit which with a little work can be placed inside many Amiga cases for that authentic look.

But what if we told you you could get a reliable power supply, with enough juice to power your Amiga plus expansions, for less than £10? It’s true… all you need is 5V, 12V and -12V supplies and there is a Cisco server that also has this requirement and features a nice slimline power supply, ripe for the taking. You’re looking for an Astec AA21430, which looks like this

This has the voltages you need, at more than enough current so there’s no issues with an expanded Amiga running out of power. It’ll supply 5V at 9.5amps which is around double the stock A500 brick, and 3 times the A600/A1200 PSU rating. There’s also a boost at the 12V level – 1.2A instead of 1A or 0.5A depending on model, and the -12V power is five times higher – although this is only used for audio, so rarely offers any issues. The 5V line is the real win here, as that’s what the vast majority of the chips inside your Amiga uses so accelerators, external drives or even Raspberry Pis acting as scandoublers will benefit.

(Whilst we’re talking Amiga power supply stats, we really cannot recommend Ian Steadman’s website enough for this type of detail)

Other benefits of using this is that it has a standard Kettle lead IEC mains input, so you can tailor your mains lead length and also pack it away for easy storage, plus a mains switch built into the chassis.

To make this compatible with your Amiga, you’ll need an old Amiga power supply with a working cable. These often turn up “faulty” or “untested” (which, let’s face it means it’s been tested and it’s faulty) on eBay. We don’t normally like destroying a working power supply for the purposes of something like this, but what you do with your own property is your business! You could also buy a length of 4-core shielded cable and the 5-pin square DIN plugs turn up from time to time on sites like Amibay or direct from some Amiga sellers.

The actual work needed to repurpose this PSU is pretty simple. The voltages are marked on the board, so once you pop it open (being careful around any capacitors if you’ve recently had it plugged in) you’ll see a purple wire marked -12V, black is COM (common, or ground), red is 5V and yellow is 12v. Desolder these and clean up the holes. There’ll be some glue that will just pull off.

Now you need to solder on the Amiga cable. We suggest desoldering this from the Amiga board, or at least cutting the cables really close, so you get the cable strain relief grommet still on the cable. Grab your multimeter in continuity test mode, and check that your cable follows the diagram below. Most seem to, but you’ll definitely want to check this before you squirt the wrong voltages into your Amiga! We wouldn’t be surprised if Commodore saved 1 penny per unit somewhere down the line and bought cable with different colours, or you may have an aftermarket PSU. Always always make sure you know which wire goes to which pin on the socket.

Now it’s just a case of soldering those wires that you definitely double checked were the right ones onto the Astec board!
(Note, an early version of this guide had a wrongly labelled power connector pinout image. This has been corrected above, with thanks to Fabian for pointing it out)

You can see that the Shield (usually yellow) has nowhere to go – for this, just crimp on an eyelet connector and attach it to one of the screw holes as you screw the PCB back into the chassis. Use an insulated one so it doesn’t make inadvertent contact. You can see this in the second photo above, and the eyelet has been bent through 90 degrees for a better fit. If you cut the cable short you may find the shield doesn’t have any insulation on, and is just a bare wire touching the braid around the outside of the other wires. In that case you may need a length of insulation to slip over it so it doesn’t accidentally short out other components.

Now you can remove a bit of rubber from the cable grommet so it sits in the cable exit hole properly – it was originally intended for a square cutout, so you’ll need to “round off” two of the corners to suit the new hole that is round at the bottom. Also shave off the opposite side of the grommet so the lid of the PSU can screw all the way down. For a final touch, we replaced the hot melt glue around the cables as they go into the board, just like you originally removed. If you peeled the Astec glue off, you can even use a hot air gun to remelt this back around the wires to save a few pennies.

Success!

Please remember this was always intended to be an internal power supply, so it may not be as well protected against sticking things in the holes around the outside. However, with sensible use this is a perfectly capable upgraded PSU for your Amiga.

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