Simple question about the PSU->floppy connector hack

[AmigaMance]

  Hi.
 I don't have any stability problems, but i want to do it anyway.
 So, i checked the voltages of the floppy connector: +12v, +5v and... 2 grounds? Or is it one ground and one shield? In that case, which is which?
 Should i connect both grounds at the ground cable of the PSU or one is enough?

  Thanks.

[pyrre]

+12v, GND, GND, +5v.

Same as the large molex connectors

[AmigaMance]

@Pyrre
 You're right.
 I just noticed that the PSU cable has 2 grounds too. I think it's just a split cable leading to 2 outputs, i don't see any differences between them.

[AmigaMance]

Ok. I short-circuit the two grounds into one, applied the hack and the power led doesn't dim on high CPU load like it used to. Or rather it does dim but it's hard to perceive now.

[Zac67]

There's two ground returns for two power connectors, that's the point. Just shorting them together for just a single ground line kinda spoils the whole point of doing the hack...

(Hint: Modern computers don't use a whole bunch of power and ground lines just for fun.)

[AmigaMance]

@Zac67
 I'm not sure which ground belongs to the +12 and which to the +5v. :-? It would be a simple task if the PSU cable was the standard, 4-Wired +12-0-0-+5, but i cut a 6-wired one and connected the appopriate voltages to the floppy connector.
 I did that, simply because i don't use these 6-wired plugs and didn't mind waste them, while i use both of the available +12-0-0-+5 plugs.
 Then, i measured the voltage between the two grounds, saw that it was near zero and so i short-circuit them.
 Is this dangerous or just inefficient?

[r6stu]

What hack are we talking about pleasE? is there a link?

Thanks

[Zac67]

Which of the ground returns you use doesn't matter, but the point is to use one ground return for each power line - the point I'm trying to make is that it's not only important to properly supply power to a device, you'll also have to supply a clean ground return.

There's only so much current you can run through a wire, depending on diameter/cross section (and material). If the line is too weak/thin it'll cause a voltage drop which will in turn cause all kinds of problems.
But you can't use arbitrarily thick wires, so you use a whole bunch of them. Bridging them together to save lines doesn't make sense in that way.

I once repaired a PET that had been sitting in storage for 15 years - after fitting a 32K memory expansion it just wasn't working properly any more. The main problem were the power supply cables that were getting quite warm,, so I replaced them with the thickest I could find. Tweaking the power supply from 4.8 to 5.2V did the rest and the PET worked like a charm.

[AmigaMance]

Which of the ground returns you use doesn't matter, but the point is to use one ground return for each power line - the point I'm trying to make is that it's not only important to properly supply power to a device, you'll also have to supply a clean ground return.

 Got it! Thank you Zac. I will connect each ground properly.

[pyrre]

Cut a whole molex cable from a dead psu, and solder it into the wiring of your amiga. and connect the smaller molex connector to the floppy output on the MB.
That is what I did, and it works like a charm.
I have no flashing or dimming in my power led at all....

[AmigaMance]

r6stu wrote:
What hack are we talking about pleasE? is there a link?

Thanks

 I'll have to search for a link but it's fairly simple:
This is mainly useful for heavily expanded Amigas. You just use a split cable to send current from the power supply unit, straight to the floppy disk connector.
 This will ensure that all cards will get enough power.

[rkauer]

 You don't need to bother with shorting the two black cables (GND), but you need to route BOTH of them to both ends.

 The reason is simple: they ARE SHORTED in PSU, anyway. So short the cables elsewhere don't harm your computer in any form.

 Using two mini-molex (intended for connection of floppy drives) and solding both to the PSU connector makes the voltage drop-out a minor problem and free the middle lay (on multilayer PCBs) current.