Atx Psu

Hi,

Sorry for bothering you with such trivial issue but I'd like to finally find out one thing: in some thread (no link due to short circuit in my memory ) I've read that 3 resistors must be put into 5V line to stabilize ATX PSU working with Amiga 1200.

It was suggestion one of AMiga gurus from here - Zetro or somebody's else (please forgive my bad memory.. as I said.. short circuit ) in thread with modding such PSU. I'd like to make perfect mod, so it's why I'd like to find out:
* which resistors (47k ? 100 k ?)
* how (serial mount ? to ground ? between 5V lines/rails ?)
to make it work.

Thank you for clues, I hope I'll find out that making this knowledge public at the same time

[john1979]

I have heard of using a resistor on an ATX PSU to generate load and so help to keep the PSU running.

Last post on this thread:
http://eab.abime.net/showthread.php?t=58348

Also this thread uses a resistor on an ATX, again to help keep it running:
http://eab.abime.net/showthread.php?t=31025

I've been running an Antec 350W on my 1200 for some time without any resistors and all seems good so far.

[Retrofan]

I think I will be selling one soon, as I bought two ATX. But it will be slighty different, with a cut in the upper part, to breath better (and 'cause my case -the A500 one- was broken). Well, in fact I did it today, but I've just bought the voltmeter from China.

Anyway, you have all that you need in my post:

http://eab.abime.net/showpost.php?p=819819&postcount=89

and this talking about the resistors:

http://eab.abime.net/showpost.php?p=821327&postcount=97

Many thanks, Retrofan - I meant your first link and I was looking for its explanation which you just gave me in second link.

So I'm going to stabilize 5V rail with some 20W res, and fulfill 10% of load @ 3.3V rail. Main thing is such resistors are relative expensive 2.80 quids for good 20W res 1% tolerance

[duga]

I've only tried without any resistors and didn't get it to work. The power LED on the A1200 turned green but it didn't boot. Maybe a resistor was the missing link.

[Retrofan]

With my psu it boots with or without them. You must measure the volts in the pins before trying anything in the miggy, anyway.

In fact I had a short inside the power cable (I changed the connector and the cable) and thanks God I measured it first, 'cause it was giving around 16volts.

Originally Posted by biuro74

... Main thing is such resistors are relative expensive 2.80 quids for good 20W res 1% tolerance

... And they are big and ugly .

Edit:
And remember that

Originally Posted by rkauer

Up to 200W you don't need a power-wasting resistor. The Amiga itself will care about the minimum power consumption.

Originally Posted by duga

I've only tried without any resistors and didn't get it to work. The power LED on the A1200 turned green but it didn't boot. Maybe a resistor was the missing link.

I don't think so. I think it's the amps you've got in the lines (your PSU). You need around 20 amps in the 5volts line.

[Stedy]

Hi,

The last time I had to put some load resistors on an ATX PSU to stabilise it was back in 2000, when a development board only used +3V3, not 5V. Newer ATX supplies are stable without load. I've used ATX PSUs with 5V only at 1-7 Amps and/or just +12V with no issues. Just ensure you connect PS-ON (green wire) to ground.

Have successfully run Amigas from 60-450W ATX PSU's. Of course I use one of my adaptors, which also connects all the supply pins together, which helps if the PSU has remote power sense If there are additional, smaller wires in parallel on the 20/24 way ATX connector, the PSU has remote sensing.

Ian

[Retrofan]

I tried your adaptor (and I've seen it's the same adapter or adaptor) with another ATX PSU (new) with 12Amps in the 5volts line and it didn't run at all.

And it has exactly:
3.3v@17A
5v@12A
12v@10A
-5v@0.3A
-12v@0.5A
5vsb@1.5A
Output:3.3v & 5v Total output 65W.
It's a 200W PSU.

I tried your adaptor with the ATX PSU I'm using now and it worked without problems.

And I've heard other places also about that it needs at least 15Amps in the 5volts line.

http://www.amibay.com/showpost.php?p=46648&postcount=2

Originally Posted by Stedy

... Of course I use one of my adaptors, which also connects all the supply pins together, which helps if the PSU has remote power sense ...Ian

That uses to be the orange cable, right? But I don't have that function in my PSU (less problems).

[Stedy]

@Retrofan

Something in your Amiga setup is causing the over-current limit of the ATX PSU to kick in. Had a similar thing on a unit @ work, normal current was 2.5A, measured 12A on power on. Used some clever tricks to fix the card @ work.

What is the specification of your A1200?

[Retrofan]

Thanks Stedy, but that PSU is RIP... I mean, I don't need it as I bought 2 ones of the last model that I'm using without problems.

Your adaptor worked without problems in both, and I'll got running now 3 ATX psu's (4 if I count the Amigakit one), so I've got no interest in using that PSU.

Thanks anyway and for your help running them too.

[orange]

I never had to use those resistors, either. Then again, I've used 'weaker' and a bit older ATX PSU (think its 350W). it depends on the PSU. because I have an old SMPS (AT) that seems to work with no load at all!