View Full Version : Wanted A4000 PSU

15th May 2011, 16:51

I need an A4000 PSU in perfect working order, if possible with a silent fan already mounted.


15th May 2011, 21:44
I could also use some help about buying an ATX replacement along with the adapter from amigakit.


It seems that 12,5 cm wide PSU might fit the A4000 case screws but would leave space underneath, like this one:


How to fit it securily?

And more important, would the PSU actually turn itself off with the switch from amigakit?

I do not like those ATX PSU that are always on.
I ahae not owned a PC tower since the AT era with good old power switch, only laptops, and i am not confotable with the ATX standard.

15th May 2011, 21:52
Yes, it will turn itself off (output section).

For completely turning off you may have to find one with an ON/OFF switch on the back. Only very good ATX PSU models have this switch.

For the space, see this awesome thread (http://www.amibay.com/showthread.php?t=3539): Keropi's approach look this way.

15th May 2011, 22:56
Great link thanks.

Would you have any specific good PSU with a switch at the back to recommend?

16th May 2011, 02:38
Not from Europe, I'm afraid. You need to ask the locals. ;)

Just remember those newest ATX24 connector units needs around 15 to 20% of the 3.3V rail maximum rate to work properly or they will not regulate the other voltages.

Be warned, although a high wattage simple resistor will do the trick ( 0.47 Ohm x 50W soldered directly inside the PSU to keep the resistor cold).

16th May 2011, 20:28
The best PSU i have found so far is the ADVANCE Micro ATX - 120x125x63mm - PX-3300P08 -300W

It has a 125 mm width, a power switch but may be to weak on the +5V at only 12 A.

+ 3.3 V: 20A
+ 5 V: 12A
+ 12 V: 20A
- 12 V: 0.5A
+ 5.5 V Sb: 1.5A
Vitesse ventilateur 1200 tr/min
Entrée: 115/230V

What do you think?

MicroATX PSU with more than 20A on the +5V are a lot bigger.

By the way, would someone have an original A4000 PSU handy to give me the exact dimensions?

16th May 2011, 20:41
On this specific PSU you need a charge of 4A on the 3.3V rail to stabilize the other voltages, so this means a 0.82 Ohm resistor (good luck finding one!) per 10W dissipation at least.

If you don't find one, use TWO 1 Ohm /10W resistors IN PARALLEL to draw ~ 6.6A from the rail. This will suffice to force the PSU to regulate the other voltage rails to safe Amiga operation.

Just don't use much Zorro cards on this Amiga because the relatively weak +5V rail.

Now, if you can measure the A4000 PSU height & width you may find something better who fits on the available space.

16th May 2011, 20:53
Well, unfortunately, i won't be able to add any resistor myself. For such a work, i can only count on Cosmos, who lives 400 km far from me. Sending him all my parts has already drained so much money from my pocket in shipping cost that i could buy another A4000.

I need to find a good enough PSU at once or find someone to build a better one for me.

The A4000 is rather limited in slots, unlike the A2000. Would 4 zorro boards and 2 ISA boards be too much?

Could you explain a bit more the concept of charge on the 3,3V? I do not understand what it means. Is the 3,3V used on the amiga?

16th May 2011, 21:28
The 3.3V is not used by the Amiga at all unless you are using a hacked Meditator 4000Di and a Radeon92xx.

In order to make ATX stabilizes ALL their voltages, some charge (consumption) must be put on the 3.3V wires. That's where the pair of 1 Ohm x 10W resistor goes. Without they the 3.3V will not have any consumption, rendering the whole power brick VOLTAGES unstable.

But of course you can add those resistors directly on the ATX connector, just notice the pair will heat a lot. You also must make they secure in the socket.

Four Zorro boards and two ISA will consume a lot of juice, prefer to find something with at least 28A on the +5V rail for secure operation.

16th May 2011, 21:43
I understand now :-)
Do you think that the Amigakit adapter does the 3,3V trick?

I have mailed Amigakit already about this adapter but i have no answer.

17th May 2011, 00:17
No, it does not. You must solder the resistors inside the ATX PSU by removing the 3.3V wires (orange) and solder the resistors instead, with the other resistor leads to ground (black wires).

Nothing really hard to do if you have a simple potent soldering iron (60W is preferred) and some solder.

17th May 2011, 12:19
Ok, it seems Cosmos was not aware of that when he made me the modified ATX PSU i used for a month. May this be responsible for its death?

17th May 2011, 15:39
Ok, i have finally bought from AmigaCenter France an original A4000D PSU. I hope it won't be too noisy.
Thanks rkauer for the advices.
In the meantime, i will look without hurry for a good suitable ATX PSU for the future :)

17th May 2011, 23:40
Always try to grab the most powerful one your system may need. One in the 400-to-550W range with 30+ A on the +5V rail is your goal here.

Check if it fits inside the Amiga, of course.

18th May 2011, 14:26
Ok, i have finally bought from AmigaCenter France an original A4000D PSU. I hope it won't be too noisy.
Thanks rkauer for the advices.
In the meantime, i will look without hurry for a good suitable ATX PSU for the future :)

How much did this cost you

Thanks james

4th June 2015, 17:15
I´ve got an original PSU from A4000, to sell, are you interested?


Best regards.