Dreamcast PSU using PicoPSU

Whilst I was looking at emulating the GD-ROM drive, I saw that some people were replacing the Dreamcast PSU with an ATX PicoPSU.  I had a DC with a blown PSU, and I had a PicoPSU which I purchased years ago, but since abandoned the project it was meant for.

Update 2019

There’s a really nice solution to this on github by chrisz2600, a custom PCB which has links to the connectors needed.  I wanted to make one but the main power connector between the motherboard and the PSU was too expensive to send from USA to UK where I am, so I simply desoldered the connector from a broken DC PSU.

Note – I’ve made a couple of these, but since I had some interference on the video signal, I ended up only using Mini-Box PicoPSUs.

I started by adding a small bit of solder to one of the pads for the 10K resistor.

I heat the solder up again whilst sliding the resistor into place using some tweezers.

Then it’s a case of heating up the other end of the resistor and the pad at the same time and then touching some solder to the pad, it will quickly transfer onto the pad and the end of the resistor.

I test fit the connectors, the connector for the Power Button can be attached either way, it doesn’t matter.

Just like the resistor, I heat up the pad and the leg that is being soldered at the same time, and then touch the solder to the leg or pad and it will make a good join.

The rest of it is just plug everything in!

If your PicoPSU is a 20 pin model, it will only fit one way so don’t worry about messing it up.

The PicoPSU that I’ve used here is the PicoPSU 90, the external PSU I’ve been using is a 12V 2amp model – I’ve used this combination on Dreamcasts with the original GDROM drive and the GDEMU.  I prefer the 3D printed solution for the power socket by collingall – Greg Collins.

Original Post

I’d seen some photos of this mod elsewhere where people have removed the connectors from the DC PSU that are used for the power pins and power switch and re-used them rather than trying to find alternative connectors that fit, or simply hard wiring it.

Making the PSU Board

I liked the idea of re-using the connectors, and rather foolishly thought I would re-use the circuit board also.  It took about 5 minutes using side cutters to snip all the legs off of as many components as I could on the PSU board.

Another 10 or 15 minutes or so were spent heating the solder up on the underside of the board and whilst the solder was molten I would shake/tap the circuit board against the desk to remove the remains of the legs of the components.  This took much longer than I anticipated though.

Some of the larger components needed me to use a Solder Sucker/Desoldering Pump to remove the the component.  Occasionally it was necessary to add some additional solder to help melt it all to be able to remove what was already there.

I left the power pins connector along with the power switch connector on the board to re-use.  I couldn’t decide what I was going to be doing with the PicoPSU power socket, so I left the original figure 8 power lead socket on the board.  Later on I decided to remove it – I didn’t plan this very well, I was making it up as I went along!

Original DC PSU stripped of parts - upperside

Original DC PSU stripped of parts - underside

This is a pretty simple mod really.  The DC PSU board has the voltages labelled on it.  Combine that with the pinout of the ATX connector and it’s a case of linking them up!

This is the diagram I followed from SMPS Power Supply

ATX Pinout 20 and 24 pin

Rather than solder wires to my PicoPSU, I grabbed a spare ATX Extension and decided to chop that up.

Looking a the DC PSU Circuit Board, we need 3.3v, 5v, GND, GND, GND and 12v.  According to the diagram that’s Orange, Red, Black (x 3) and Yellow that we’re working with.  On the extension lead I’m using, I chose the relevant pins and removed any that aren’t needed.

I forgot to photograph this – maybe I got carried away!  Here’s a photo of one of the pins after I had removed it.  You’ll see two arms on it which need to be squeezed in to be able to remove the pin from the ATX connector.  I used a long needle/pin to push one side in and then the other before pulling the wire and pin out of the connector (I’ve got a molex removing tool somewhere, but couldn’t find it).

Pin with bent arms on the left.

Don’t forget to leave the Green wire and another Black GND wire – when the Green wire is grounded an ATX PSU interprets that as time to switch on.

I decided to mount the ATX socket near the power pins connector so that I could keep the wires from the ATX socket as short as possible.  The soldering points are on the underside of the DC PSU board, and I decided to route the ATX wires through the board.

Because the wires are a thicker gauge than the legs of the components, it was necessary to enlarge some holes.  I was too lazy to go and find my drill bits so I used my scalpel to get the job done.

Holding the ATX socket where I wanted to mount it, I started to trim, strip and tin the wires coming from it.  Ensuring to leave enough wire for it to reach the hole I had for it and go through the board allowing me to solder it.  Leave the Green and a Black wire alone for now – you want them long enough to reach the power switch connector later on.

Whilst enlarging the holes remember to check that it’s the correct size for the stripped wire to poke through.  I chose which holes to enlarge by looking for existing holes near the solder pads for the power pins connector.

Increasing hole size for wires.

Here I have done four out six of the holes needed.

Example of hole size

After enlarging them I scrape away around the holes to give the solder something to stick to.  I’ve scraped away the green coating which now exposes the copper on the board.

Solder points

Here I’ve soldered the first wire in place – the Yellow 12v wire.

First wire soldered in place

I then started putting the Black GND wires through and soldering them in place – you get the idea!

2 GND wires poking through ready to be soldered

Last bit of soldering now, I route the Green and final Black GND wire around to the underside of the board and solder them to the two outside pins of the power button connector – it doesn’t matter which one is soldered to which pad.

Power switch wires soldered to the connector pins

First test fitting

This gave me enough to power on the DC now.  I’m using a 12v 4amp PSU to power the PicoPSU.


Switched it on and it's working :-)

Mounting the PSU Socket

I didn’t want to drill a hole in the case of the DC and I wanted this project to be a direct drop in replacement.

I considered using a 3D printing service and designing a piece that slots into the hole in the case for the figure 8 socket.  For now though, that’s beyond me.  Instead I decided to make something a lot simpler using junk I had to hand.

Update – the talented collingall has released the files to get a perfect fitting socket 3D printed, thank you!

This is the idea I had – sandwich three pieces of plastic together to fit in the opening for the figure 8 socket.  With a hole running through them all to mount the PicoPSU socket.

PicoPSU socket holder layers

I found some clear bits of plastic that were actually dividers for a storage box which I no longer use.  The plastic was quite soft – which meant it was easy to cut with a knife, scoring it a couple of times and then snapping it (like in this guide).  It wasn’t brittle either – meaning it wouldn’t crack when cutting or drilling it.  There were varying thicknesses of plastic bits I had, so I chose one that was the closest to the thickness of the narrowest part of the case opening for the figure 8 power socket.

Existing socket hole.

Another shot of the existing socket hole.

Once I had chosen the plastic, I drilled some 8mm holes in it.  This was the size that I needed for the power socket that my PicoPSU had already attached.

I drilled the holes first because I guessed it would be easier to drill them in the larger pieces of plastic.  I think it would be difficult to hold and drill the plastic when it was smaller.

Holes drilled ready for cutting strips

Time to cut out three strips which are the same as the height of the socket hole in the DC case.  I didn’t measure this, I held the plastic against the hole and marked it.

First strip cut to the correct height

Once I cut the first one, I used that as a template for the other two.

Using first strip as template.

Now you’ve got three strips of plastic all about the same size (which I forgot to photograph).  You need to be trim them to length now, but they are not all the same length!

One shorter piece needs to be the right length to fit in the narrowest part of the case opening.

Existing socket hole.

Finished cutting to size.

The other two need to be the length of the widest part of the case opening.  Once you have them cut to size, poke the PicoPSU power socket through each of them.  Remember that the shortest piece of plastic is sandwiched between the longer pieces.

Mounted to PicoPSU socket. Mounted to PicoPSU socket.

The nut which holds the socket in place is also squeezing the three bits of plastic together.  I like this as it means – no glue needed (also means I’m not going to be sticking my fingers together!)

Replacing the screws.

Nice and neat!

Final fitting

Socket holder in place and secure.

If only I had found some white plastic.

I’ve been too lazy to trim the wire that connects the socket to the PicoPSU.  If I did do that though, I could use all that extra space to perhaps hold a circuit board for the internal VGA mod, and maybe even a butchered up VGA to HDMI adapter?

This is the first mod I’ve done for quite a while.  Nothing too adventurous, but I’m pleased with the final result.