Compatible MicroPSU for A4000 desktop

Templar

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Helloz my friends.

I need your assistance, please (Zetr0, rkauer.... etc)... :)

I want to buy a MicroPSU to put it inside my desktop case, but what's happening with the DC outputs?

Which one is fully compatible with my Amiga? Does anyone know what to check before buying such a MicroPSU?

:help::help::help:
 

rkauer

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You mean mini-ATX PSU? Pretty much all will work, but notice that a lot of those doesn't have the -5V reference rail.

You must create the rail yourself if some Zorro card refuses to work after the conversion.

Dead easy to make using the -12V rail, a LM7905 and one 47uF capacitor on the output and and a few wires. :)
 

arnljot

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I think you´re speaking greek now rkauer. And despite Antonis being a native of Crete, I think he´d agree with me on this one.

You need to dumb it down for us :LOL:

-5v, is that ground or? The Amiga 4000D Skynet is labled, like PC supplies, to have +12V, -12V and +5V.

Now, the Amiga 4000D motherboard plug has two more leads, the Power Good signal and an additional ground, is this the one you refere to as -5V?

Doesn´t modern PCs use +5V. I don´t know much if anything on basic electricity, I know it can make my hair stand and make magic white smoke if not treated with respect.

So if you could just elaborate a little, on a six year olds level? :D For me. :jester:
 

Kin Hell

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Kin
 

keropi

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that's not rocket science, here be keropi's "5 step program of the win" :

step 1: see the ratings on the original amiga PSU
step 2: find a mATX with better ratings on your local computer shop(s)
step 3: buy it and install it
step 4: ...
step 5: profit
 

Templar

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I'm with Arnljot with this. I don't see a -5V anywhere when I'm looking at PSUs. Or I'm missing something?

@ keropi

Can you find me one m8? Or at least point me to the right direction?:)
 

Zetr0

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I would advise directly against an mATX PSU unless you spend a good sum of money on it.

Cheap-generic mATX PSU DO NOT provide a good +5v on load for a big-box amiga, and this is an area that you need to make sure you provide the volts (at 5v or higher *5.11v*) and the amps at a good 15 or more amps.

so lets gets crazy with some amps, volts and wots? =D


lets take a look under the hood -

By reason of load, for a big-box miggy (5 volts * 15 amps = 75 watts) you will want to double this to 150 watts available on the +5volts - The reason for this is simple - the more you load the PSU the lower the voltage will drop - so the closer to a 150 watts usage you go the more the +5v will drop, in some cases below +5v causing all sorts of mayhem.

Also the higher the rating the less heat is created at lower loads.

Now, you will need to look at the +12v, for this a good 7 amps would be good, ( thats 12volts * 7 amps = 84 watts) again like before you want double this as the closer you get to that threshold the voltage will drop. so 170 watts available on the +12v will be better
__________

so how many watts do we need for our A4000 ? well thats 150watts (on the +5) and 170 watts (on the +12v) = 320watts or more

This is not all the story - the Amiga needs a -12volt and in some cases a -5v as well.

the Original power supply offers about 0.4 amps on the -12v, and about the same on the -5v for the Towers (i believe). I would suggest that you can easly achieve the needed rating with any medium quality PSU.

So if we were to take a medium quality PSU that provided us 0.5 amps on the -12 (6w) and 0.5 amps on the -5 (2.5w) a total of 8.5 watts, add this to the 320 gives us 328.5watts (yes.... its an OCD :p)


so, a good quality medium range 350watt ATX will keep our A4000 happy and wont be taxed very hard, even if you expand it to the max.


Now have a look at my album, I modified a 350 watt Q-Tek ATX for my A4000 psu that had died.

Note I also wrote ATX and not mATX.


As our good friend rakuer points out, a lot of cheap mATX PSU's dont provide -5volts you must check before you purchase -


have a look at the label on the retro-fitted PSU - you will see the wattage for the load of +5v, (180watt max) - you will also notice that the original A4000 PSU could only handle 145watt total (including +12 and -12v)

I would look at putting in or retro-fitting an ATX unit into the A4000, either by use of the original PSU housing, or modfying the chassis to accomodate it.
 
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rkauer

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Sorry, my mistake: only A2000 & A3000 boards needs -5V for some electronic signals.

No use in A4000(T).
 
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