Custom power adapter for ATX

[doufas]

Hi,

Recently I purchased this custom item to upgrade the power on my A1200:



I connect this to a 480 W PSU - Antec Truepower 480W (TPII-680 BLUE).


When I power the Amiga using this device I get wavey lines running through the screen.

Currently my Amiga has a Blizzard 1230 accel, ide CF hdd and the rest is stock. I wanted to upgrade the power for when I get my PCMCIA network card which will be here soon. The creator of the adapter believe its happening due to not enough current being needed by the Amiga.

Anyone else using a custom PSU have some tips?

[Loedown]

Read this thread, check your board revision.

http://www.amigacoding.de/index.php?topic=81.0

Also this.

http://eab.abime.net/showthread.php?p=935193#post935193

[doufas]

Hmm, that could be it but the thing is, if I use a normal power supply then it works just fine.

Still think I should try the fix I don't want to ruin the Amiga

[Loedown]

If you know how to use a soldering iron it's doubtful you will wreck your Amiga, just make sure you solder it in the right places and also make sure it's the right revision before you do it.

[RedskullDC]

Hi Doufas, et al.

Originally Posted by doufas

Hi,
The creator of the adapter believe its happening due to not enough current being needed by the Amiga.

That does appear possible.

From the specs on the Antec site:
http://www.antec.com/specs/TPII480_spe.html

+3.3, +5, +12v lines *all* have minimum load requirements.
Amiga will provide no load on the 3.3v line whatsoever.

I use an old AT supply to power most of my retro PC's. It requires a 0.5A load on the 5v line before it will work correctly.

A google search for "ATX dummy load" will provide you with plenty of clues.

Cheers,
Red

[voyager]

He is right, switching psu's need some load on their lines. Some psu's start to oscillate when there is not enough load. Your 5v lines are probably ok , 12v and 3,3v are too low for this psu.

You can put some big resistors on the 12 en 3,3 volt lines or try a different psu, most 250 watt psu work just fine. Use a wall socket with earth/ground will also help.

good luck,

[doufas]

Thanks for the advice. So it seems the PSU is the issue.

Can anyone recommend a lower wattage PSU (cheap hopefully)that should be good for the Amiga?

I am using the stock black 1 atm. However when I add my fan and wireless pcmcia to Amiga I want to have enough power...

[RedskullDC]

Originally Posted by doufas

Can anyone recommend a lower wattage PSU (cheap hopefully)that should be good for the Amiga?

Supply you have will be ok, you probably just need a dummy load on the 3.3v line to make it oscillate properly.

If you don't want to play with it, or aren't electrically inclined,
with the adapter you have, you will have to get an ATX style supply.

An ATX v1.0 supply will have -5v , whereas a V2.0+ supply isn't required to carry the -5v line. May come in handy for other projects?

There are no shortage of ATX supplies on Ebay.
Unfortunately, you are going to have to do some research on the minimum loads required on each line to see what will be serviceable.


Old "AT" type supply is easiest to work with (in my opinion).
Plenty going on Ebay Oz at the moment.
Like: http://www.ebay.com.au/itm/171248179057 for $10 plus local shipping.
Most need a dummy load on the 5v line only to operate.
However, it won't work with your adapter lead.

Cheers,
Red

[doufas]

I tried a dummy load, ie connecting a 3.5 hdd to a molex connector and there are less waves, maybe it wassnt pulling enough power as well?

[RedskullDC]

Hi Doufas,

Originally Posted by doufas

I tried a dummy load, ie connecting a 3.5 hdd to a molex connector and there are less waves, maybe it wassnt pulling enough power as well?

Putting a HD on Molex connector still doesn't put any load on the 3.3v line

Have you tried this PS with any PC components to ensure it works correctly?

Red

[Hewitson]

Theres not much point trying to guess what the problem is, measure the voltages with a multimeter or scope. Since you're in Melbourne, I could possibly help you with this if you don't have the necessary equipment.

[Retrofan]

@Doufas where did you get the cable? Linky?

The cables seem thicker than the originals, so better.

[Loedown]

@Redskull DC The adapter was originally used perfectly with a Thermaltake suppy and never had any lines through the picture on ANY Amiga I ever tested using it.

@Hewitson Good of you to offer but I will sort it out.

@Retrofan The adapter was originally made by Amigamaniac and when he sent it to me I got him to send me a few more A500 / A1200 connectors with flying leads. Nathan remains one of the good people from the scene and it's a shame that he just disappeared, if anyone knows how to contact him?

I built another adapter with one of the spares I had here from the original bunch I got Amigamaniac to do but I wasn't satisfied with the heatshrink job I did so I sent the original adapter rather than faff about with the new adapter. The problem is that the power supply being used is either faulty or needs the +3.3V rail loaded up as Redskull DC pointed out, something that I didn't do because it never gave me any issue. I have offered two solutions to OP regarding the adapter.

[doufas]

I'm going to try testing with a couple more PSUs this week and let you knwo the results first.

Thanks for the offer to help measure the voltage Hawitson, what suburb you in PM?

[Stedy]

@Doufas,

Your ATX PSU can supply upto 18X more than the Amiga needs! An expanded A1200 uses 25-50W, based on my actual measurements.

You can try connecting all the 3.3V power wires together in the ATX plug, this will help with the remote load sensing that will be on this power rail. Also can you shorten the Amiga power lead?

A high current PSU like yours will also have remote load sensing on the +5V. Normally this connects to a low impedance power plane in an ATX motherboard. The Amiga power-lead is a nice lumped inductive load with a large capacitance at the other end, perfect for upsetting the regulation.

A low wattage PSU, like the picoPSU, is ideal for the Amiga as it is stable with no load (confirmed by studying the design) and the 60-120W power rating more than adequate.

[doufas]

Haha, yeh I'm starting to think I went overboard with this.

Only reason I got it was because I read some other posts that the stock black power box is pretty crappy for the Amiga and didn't provide enough power if you have a few addons.

I only have an accel card, cf hdd and wireless pcmcia network and it seems to run fine on the stock power (i was planning on adding a indivision in the future maybe).

Wishing I got the picoPSU, my bad, could of gotten it for just a tad extra.

https://www.mini-box.com.au/picoPSU-...wer%20Kit.html
+
http://www.ianstedman.co.uk/Sales/Ia...talogue_3.html

I can connect a picoPSU to this cable right?

Thinking of doing that and just getting a small enclosure and copying this design:

http://www.amibay.com/showthread.php?t=41918



Next plan would be to power the 2 12v case fans I have via the floppy power, is that a good idea or ... ?

[Stedy]

@doufas

You can safely use a picoPSU with your adaptor cable. You will not need one of the ATX adaptors I sell as you have a mating ATX connector into which you plug the PSU. The only change I would make to your cable is to connect 2-4 +5V and a similar number of 0V/GND connections together. This lowers the cable resistance and helps ensure any current feedback signals are connected.

The boxed picoPSU design linked on Amibay, and one at A1K.org, is a good place to go.

Ian

[Retrofan]

I would like to make an APower, but who knows what psu did Mechy use?

http://www.amiga.org/forums/attachme...1&d=1302220256

[doufas]

@Steady

I have sent my cable back and decided to make use of your adapter.

I checked the site, but is there is a guide step by step I can follow? Should I go with an internal or external?

[Stedy]

Hi,

All manuals and install guides are here:
http://www.ianstedman.co.uk/Amiga/de...x_adaptor.html

Your 450W PSU is seriously over specified. The A1200 only uses 20-25W with common add-ons/accelerators. Using a 450W PSU at 5% load is not good for efficiency or ensuring stable supply regulation.

I like the picoPSU as they are small, neat and stable with 0% loading. A 60W model is fine for the A1200, some users use the 120W PSU in A2000 with no issues.

The choice of internal or external is down to your building skills.

Ian