11 replies to this topic

[thgill]

I mentioned in the other thread about having installed a PicoPSU inside my STe and thought people might want some photos. 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. I have always thought the internal power supplies on STs were there weak point.

[DarkLord]

Looks like a good job there. Thanks for the pictures.

I've got the 120 PicoPSU here. I'm seriously thinking
about using it in my STacy. Unfortunately, the internal
setup for the STacy's power supply board is much
different than an ST.

So...since I've got the Ultrasatan, a fan, and a converter
for the replacement El Sheet display, and a 5v lead to the
PAK 68/3 accelerator board, I was thinking about maybe
hooking 12v off the STacy's original P/S board to power up
the Pico, and then using the Pico to drive all those items
above.

That way, there would actually be much less being drawn
off the original STacy P/S.

Whatcha think, would this work? Thanks.

[Fox-1 / mnx]

DarkLord, on Sat May 26, 2012 12:06 AM, said:

I was thinking about maybe hooking 12v off the STacy's original P/S board to power up
the Pico, and then using the Pico to drive all those items above.

That way, there would actually be much less being drawn off the original STacy P/S.

However not impossible, it's advised to use a single power supply to power all components that reside in a single unit.

[thgill]

I think the bigger problem might be overloading the 12 volt rail on the STacy power supply.

What's it rated for?

[krupkaj]

nice. It is a pity pico psu has not -5V. I would like to use it in my TT

[thgill]

You could always use a small 7905 voltage regulator to get the -5 volts.

[krupkaj]

good idea, but I am not sure if the -12V line is strong enough. It would be nice to measure the current which TT draws from these "-" lines,

[thgill]

7905's are usually rated up to 1 amp. I would be surprised if the TT drew more than a few hundred milliamps from the -12v rail.

[DarkLord]

Fox-1 / mnx, on Sat May 26, 2012 3:33 AM, said:

However not impossible, it's advised to use a single power supply to power all components that reside in a single unit.

Hmm, can you give the reasons for that? I'm not doubting it, just curious as to why (other than convenience).

I'd love to have the Pico do everything, but have you seen the internal connections for the STacy's P/S? Its not the
(relatively) simple connection that a standard ST is unfortunately.

[DarkLord]

thgill, on Sat May 26, 2012 11:03 AM, said:

I think the bigger problem might be overloading the 12 volt rail on the STacy power supply.

What's it rated for?

Not sure, I'd have to check that. Right now, it's just powering the UltraSatan. It used to power
the 20meg MFM hard drive, so I was thinking if it could do that, it would handle the Pico since
the Pico is supposed to be low reqs.

[Fox-1 / mnx]

DarkLord, on Sat May 26, 2012 2:50 PM, said:

Hmm, can you give the reasons for that? I'm not doubting it, just curious as to why (other than convenience).

Convenience is indeed one reason.

The Atari and Pico PS' are both "switching" types, but different. They don't switch at the same frequency so there is a (small) chance one will interfere the other which may result in drifting voltages.

More important, a PS creates a ground relative to it's output voltage (or the other way around, doesn't matter), like, the +5V output is 5V above ground, where ground is 0V for that PS, but it's relative. It may just be the ground is in fact +2V while the +5 output is +7V. This will still give a +5V output when compared to that ground.

When using 2 PS' (in a single unit designed for single PS usage) you always have to connect both grounds together, so if 1 PS has ground at +2V and the other has ground at 0V there is a 2V difference. No problem for a running system as both grounds will be forced to the same level (they're are connected together) but this is only true when running. While powering on both PS' there is a small delay until the voltage output is stable but it's almost certain this delay is not the same on both PS' so during that time there is a chance your output voltages are too high. It depends on the duration of the delay and the amount of difference if it can do any harm or not.

In many cases it'll just do without any harm but it's up to you to decide if "many" is enough.


Not connecting both grounds is no option as it can be pretty devastating. This is (was) one of my 130XE's:



The result of relying on main power outlet earthing as the ground connection only to discover there was none at all on the meeting we attended...

DarkLord, on Sat May 26, 2012 2:50 PM, said:

I'd love to have the Pico do everything, but have you seen the internal connections for the STacy's P/S? Its not the (relatively) simple connection that a standard ST is unfortunately.

-Do you know what pin expects what voltage?
-Are all those voltages present when using a Pico PS?
-Do you have a header to connect to the STacy pins?
-Are the pins standard spacing?

If so, put a header on a small piece of vero board, make the connections on the board, plug it in.

[thgill]

I just looked up some pics of the Stacy power supply and it doesn't look like it would be that hard to replace, unless I am missing something.

DarkLord - have some pics of your Stacy PSU?