DIY: Retro fitting a PicoPSU into a STf/fm/e machine

[thgill]

I posted this originally over at AtariAge, and thought some folks here might be interested in it.

This is the second one I have done and I have the install process done pat. This is the 80 watt PicoPSU with 80 watt 12 volt brick.


I retained the original power switch and installed the 2.5mm dc power jack in place where the original AC cord plug was. This Pico plugs into an ATX 20 pin male connector that is then wired to the original 6 pin ST motherboard power connector.

Reason I did this was because this machine is a UK PAL machine with the original 220v power supply and since I am in the US it wasn't going to do me much good. I have always thought the internal power supplies on STs were there weak point.

[spiny]

awesome stuff

I like the way you have kept the PSU base plate, very neat and tidy

[ralcool]

And if you look at it, the question of how to fit a MegaBUS or VME slot to an older ST is answered.

I've said before how much I love the PicoPSU.... can't wait to tell you why.

Muhaha.. Nice job there man... Might have kept a spare molex for internal drives though.

ST.

[thgill]

Muhaha.. Nice job there man... Might have kept a spare molex for internal drives though.

Its still available. Those two little white connectors on top the picopsu pcb allow you to attach/detach the molex power connectors in case you don't need them. If the need arises, I can just plug it back in. The smaller of the two white connectors is for an optional P4 power cable.


edit: Ohh, and now that I think about it, you could easily cram this down into a smaller space if you desolder the ATX connector and hardwire the power cable directly to the Pico. Take up even less room inside the machine.


Also, the Pico stays pretty cool too. I have ran my STe for hours and hours on end with a looping demo and the top of the case was barely warm to the touch.

[Decky]

This look excellent. Just wondering if it's something that will be made available to us to buy?

[1st1]

THIS is a pretty cool idea! Would it also work for other devices? Thinking of Falcon, TT, Megafile, ...

(I have a Megafile without PSU, would such a PicoPSU supply a 5,25 inch harddrive...?)

[Methanoid]

Looks very neat. Does the Pico provide +5v, +/-12v and Ground for connecting as an internal PSU on the original 520ST?

http://www.atari-forum.com/viewtopic.php?f=15&t=19216 has the pinouts...

Was thinking to fit a Pico and a HxC Floppy emulator inside an original 520ST

[DarkLord]

Can we take this a bit further, other than just STf/fm/e machines?

If I can find/scan the schematics for the internal power supply of the STacy, does
anyone think we could successfully (as in NOT fried, died, and laid to the side!)
wire a Pico unit in?

That would be bloody marvelous. More room, more power, cooler operating
temperatures... <dreams>...

[Atarist8te74]

Hmmm I have an old pico psu floating about that would be ideal for this!

I have an STE here that has decided that powering a 5volt external disk drive is just too much. Its nothing a decent wall-wart adaptor wouldnt solve but when space and sockets are a problem, tapping power from anywhere available seems easy at the time.

[TheNameOfTheGame]

This power cord interests me. Most cords from wall warts are so flimsy. This one looks sturdy. Could you post the model # of the brick you are using?

[troed]

I posted this originally over at AtariAge, and thought some folks here might be interested in it.

This is the second one I have done and I have the install process done pat. This is the 80 watt PicoPSU with 80 watt 12 volt brick.

Indeed we are Any additional insights you want to share? I'm on my way to mount an HxC floppy emu internally in my STe (in addition to the original floppy, with an A/B-selector switch) and I'm interested in doing your pico PSU mod at the same time. An additional benefit is increasing the available internal space for mods!

Is 80W enough for an STe with some to spare or do you recommend going for a 120W model?

[Methanoid]

I posted this originally over at AtariAge, and thought some folks here might be interested in it.

This is the second one I have done and I have the install process done pat. This is the 80 watt PicoPSU with 80 watt 12 volt brick.

Indeed we are Any additional insights you want to share? I'm on my way to mount an HxC floppy emu internally in my STe (in addition to the original floppy, with an A/B-selector switch) and I'm interested in doing your pico PSU mod at the same time. An additional benefit is increasing the available internal space for mods!

Is 80W enough for an STe with some to spare or do you recommend going for a 120W model?

Ditto.. same mods planned. Love to see more pics & guidance.

[DarkLord]

Don't know how much it applies to other ST models, but Alan H., over in my First
PAK board attempt message thread has come up with a clever way to replace the
internal STacy PSU.

He simply fed power from another source *back* into the 2nd floppy drive
connector, and that powers the STacy motherboard. No having to fool around
with that complex internal PSU setup/motherboard headers.

He's using an ATX power supply at the moment, while he works on some other
mods, but the concept should work with the PICO as well. Anyway, when I get
all my stuff together, I'm going to try it with my STacy. Can't wait.

photo.JPG

[calimero]

you could put entire brick in STe case!

And why use 80W? How nany Watts have original STe PSU?

[troed]

Is 80W enough for an STe with some to spare or do you recommend going for a 120W model?

And why use 80W? How nany Watts have original STe PSU?

I managed to find an/the answer in another thread:

"In STFM machines the PSU is rated at 35W. However some later machines (forget which) have PSU’s that are rated at 50W. But these are the maximum ratings. I would expect the normal running power to be around half that, so about 17W to 25W."

http://www.atari-forum.com/viewtopic.ph ... 00&start=0

So I'll probably go for an 80W as well. I already have some 12V bricks laying around that are specced high enough.

[tresas]

Nice work!!! I have a few questions because i don't know many thinks about electronics! Where did you find a 20 pin ATX to 6 pins ST adapter? Can you keep the old original (pc type) AC chord with new PicoPsu? The new PicoPSU does it have the exact voltage supply for the ST? Thank you!

[DarkLord]

Thgill - do you have to do something to a PICO to get it to work, if its not
plugged into an actual motherboard? I noticed you used an ATX connector.
You know how you have to ground 2 pins on an ATX power supply to "fool"
it into thinking its connected before it will work?

Reason I'm asking is, I've got the 120w PICO model here now, and I can't
get it to power anything up. The green light on the brick comes on, the green
light on the PICO itself comes on, but nothing will work off of it. I had hooked
it up to my STacy according to Alan H's example above and got nothing. So
then I just tried hooking up devices to the molex connnectors and even a
floppy drive straight to the PICO floppy connector.

Nada. Nothing will come on at this point.

Thanks.

[DarkLord]

Never mind, got it.

That's what I had to do, I had to ground/connect pin#14 to any ground. On a normal
ATX power supply, that would be the green wire and any black wire.

Oh, there is a 3rd connector on the jack for the power brick I got - is it supposed to
go to ground somewhere inside the ST? It's not hooked up, as is, from the factory.

Thanks.

EDIT: I went back and took another look at your original pictures - it looks like you
didn't use that 3rd prong either.

[DarkLord]

Hmm, if you were going to put a switch in, would you put it inline with the black
or white wire on the PICO power jack? Or does it even make a difference which
one? (see pic)

Thanks.

picoPSU-120-big3.jpg

[DarkLord]

Just FYI, I ended up breaking the white wire for my switch. I tried the black wire
first, because according to the back info panel on the power brick, that is ground.

However, when I did that, with the power jack bolted into the backplane of the
STacy, the switch wouldn't work - I guess it was grounding through the metal of
the jack and the backplane. With the switch in the on or off position, when you
plugged the brick into the jack, everything would power up.

Everything seems to be working like you would expect with breaking the white
wire.

Thanks.

[SoundDoctor]

Just FYI, I ended up breaking the white wire for my switch. I tried the black wire
first, because according to the back info panel on the power brick, that is ground.

However, when I did that, with the power jack bolted into the backplane of the
STacy, the switch wouldn't work - I guess it was grounding through the metal of
the jack and the backplane. With the switch in the on or off position, when you
plugged the brick into the jack, everything would power up.

Everything seems to be working like you would expect with breaking the white
wire.

Thanks.

Hi DarkLord,

I may be missing something but...the ATX PSU requires Pin 14 short to ground for soft power on...there's your switch right there. If you look at the OP you'll see that the ST power switch on the original photos is simply shorting the green and black wire...well, that's what it looks like to me anyway. Maybe you're over thinking it a bit

<Edit> reading back through the thread you're talking about a STacy so that could make a huge mechanical difference to whats easy to implement or not. So does your requirement (I'm not familiar with the STacy) mean you need to switch on/off on the brick? You say there is a 3rd wire from your power brick that is not connected at the STacy end? Where does it go on the power brick? Wire the 3rd wire to Pin 14 / Green Wire of the PIco - at the PSU brick end install a switch to short that same Pin 14 / Green Wire line to ground through the switch. That would work neatly?

[DarkLord]

Hi DarkLord,

I may be missing something but...the ATX PSU requires Pin 14 short to ground for soft power on...there's your switch right there. If you look at the OP you'll see that the ST power switch on the original photos is simply shorting the green and black wire...well, that's what it looks like to me anyway. Maybe you're over thinking it a bit

<Edit> reading back through the thread you're talking about a STacy so that could make a huge mechanical difference to whats easy to implement or not. So does your requirement (I'm not familiar with the STacy) mean you need to switch on/off on the brick? You say there is a 3rd wire from your power brick that is not connected at the STacy end? Where does it go on the power brick? Wire the 3rd wire to Pin 14 / Green Wire of the PIco - at the PSU brick end install a switch to short that same Pin 14 / Green Wire line to ground through the switch. That would work neatly?

Right, I had to short pin14 with a ground to make the PICO work at all. It never occurred to me to make that the on/off switch.

I'm not really not very well versed in electronics at all, I just tend to "learn as I go" on all the projects I attempt to do. Its why I ask so
many questions in the forums and annoy all those people who are.

Its working as far as functioning correctly right now, as is. But if its more appropriate (safer, efficient etc) to do it any other way, I'll
happily change it.

Have soldering iron, will fire it up.

The unused 3rd pin is on the power jack itself. Not the best picture in the world, but just follow the arrow:

PICO_Stacy01b.JPG

It actually just looks like another ground to me...

[SoundDoctor]

[
Its working as far as functioning correctly right now, as is. But if its more appropriate (safer, efficient etc) to do it any other way, I'll
happily change it.

As the old saying goes...."If it ain't broke, don't fix it"

[DarkLord]

As the old saying goes...."If it ain't broke, don't fix it"

Agreed, but I'll probably go ahead and change it on my next day off, just for
safety's sake.

[SoundDoctor]

The unused 3rd pin is on the power jack itself. Not the best picture in the world, but just follow the arrow:

PICO_Stacy01b.JPG

It actually just looks like another ground to me...

It could be that pin is not used because of the way the power brick is implemented. It's likely the power brick cable only has 2 wires, +12v and ground, running to the plug from the brick end as it's DC. It's not unusual for a low cost OEM manufacturer to use the same generic connector on a range of products i.e. just not wire the contacts that are not needed. It's cheaper for them to bulk buy 1 connector and configure them differently than buy 2 or more specific types.

So the way you've done it might be the best/only way!