Hi,

I recently ordered a GTX 570 on amazon. Knowing my old 400W PSU wouldn't suffice, I also ordered a 1000W PSU (I don't need 1000W now, but I'm going to need it.) However, the new PSU arrived broken. Now I have a GTX 570 and only a 400W PSU. I need a solution until a new or repaired PSU arrives.

First I tried just using my old PSU, which surprisingly worked. But the performance is not so much better than with my old 9600GT (but at least it is better!). I'm sure it would be faster if the graphics card had the power it needs.

Now I tried using an other PSU and connecting the graphics card to it, while I keep the rest of my computer to my normal PSU. I put a cable connecting the green pin to a black pin of the main-ATX-cable of the PSU to turn it on. If I check with an old harddisk I can confirm that there is really power on the connectors.

But when I try to turn my computer on, it won't start. I hear some "clack" (from the internal speaker?) about once a second. Then after a while it beeps repeatedly, propably to inform me that something is wrong...

So does anyone know more about this topic? Can you tell me why the computer won't start when the graphics card is powerd with an other PSU and what I can do to make it work?

My best educated GUESS is because the card is already 'booted up' by the external power supply,
that some of that power is getting back into the motherboard, so its 'partially'
powered up. It has no idea how to start up from that state.
Im also hoping that no damage to MB or GPU has been done by this...

A way that "MAY" work is to splice the two power supplies together.
Be sure to read this WHOLE post before doing anything.
And I also claim no responsibility if this causes damage either ,
but I have stated any risks THAT I KNOW OF.
Of course, disconnect from the mains while fiddling with cables, just in case.
You could cause the PC to boot up at a bad time. Bad for the PC, and your wallet.


The way I would try MYSELF would be to electrically join the two power supplies together.
To do this I would securely join one or two BLACK cables from each PSU together,
if you do choose to join two blacks, join them separately, as is 2 + 2, not all into one.
If you join them all together it wont 'spread' the power out like two joints would.
And then I would join the two GREENs together, so both PSUs turn on AT THE SAME TIME.

Thats it for the power wiring, now to electrically join the two CASES together
so both are grounded to the same voltage level. If you can 'bolt' the second PSU inside
your PC case, that will do the job nicely. This is an electrical safety issue!!
It is not needed to make the system work, but dangerous TO YOU voltages could
accumulate (sometimes in seconds). THIS IS CRITICAL!!
After that you are done with the wiring. But read on anyway, its important!

Point of note: MOST psu's only fully turn on when there is enough drain on them.
Thats why you had to connect a HDD to the PSU to get it to power up its fan.
If its fan is spinning, then its is APPARENTLY fully powered up. I have never
(in 15 years)come across a situation different to this, but still... hmmm.
You video card may only draw enough power for this when it starts having to work hard,
so that means the second PSU will only turn on LATER. This is bad, potentially harmful.
So I would leave your old HDD connected to the external PSU at all times, just so
the PSU fires up completely at the same time as the main PSU.


Well, thats all I can think of, mostly.
Other that with your PSU power wires, make sure to tape them up so they cant
touch anything, or drop into any fans.
And with the CASE strap, use mains rated cable if you can, or multiple wires.


Best of luck dude!

[EDIT] I suspect you could find and buy a cable to do this
joining, but thats just more cost eh? Your choice...

Hi EvilSOB, and thanks for your advice!

Joining the PSUs together seems like a bad idea to me. While I did what I already tried I acidentally kinda did already join them together once, while only one of them was running:
The GTX 570 came with adapters from two 4-pin connectors (like for IDE HDDs) to a 6-pin PICe connector. I connected only one of the 4-pin connectors to the new PSU while the other one was still connected to the old one. I turned the external PSU on while it was like this and a case fan began running, making me aware that thereby I connected the 4-pin connector of one PSU to the one of the other. I turned the external PSU off immediately. After that, I tried to turn my computer on, but it didn't react. Only after I kept the normal PSU unplugged for like ten seconds and turned it back on, it worked again. It seems like there was no permanent damage, but it scared the hell out of me.
(Also, this kinda reminds me of old Märklin (a model railroad manufacturer) transformers which had the warning not to connect them EVER. Because apparently, the transformers also worked backwards, so if you'd unplug only one of them, you'd have 230V on the plug! And when I say old, I mean that I bought one of these in 2003 and they were not obsolete...)

About the keeping a harddisk connected idea:
That sounds like a good idea. I'm going to try that. Propably not today anymore, but tomorrow. Thanks!



EDIT: Btw, I don't think it's because some of the power from the external PSU gets into the mainboard, because it behaves the same when I don't turn it on before I start my computer.

Im quite sure its safe to connect them up how I suggest. AS LONG AS THEIR CASES ARE JOINED.
All the odd behaviour you see is when one is ON and the other is OFF.

What will happen with my design is the main PSU gets pulled on by the MB
(via the green cable), and because the secondary is joined to the same green,
it now gets pulled on at the same time. This is Zero volts when ON, 5v when OFF.

Joining the blacks is to ensure the Zero-Volt rail is the same level in both.

And joining the cases is to ensure the secondary one is properly earthed for safety.


The reason your PSU shut down for a while is normal (a 'better' quality PSU).
It realized something was 'wrong' and put itself into safe-mode for protection.
As soon as the power started flowing INTO it from the GPU-power cable, it went into safemode.
BUT, power was still flowing into it from the other PSU, and that put power to the
12V rail (powering the case fan), and the 5v rail(powering who knows what).
But the MB still saw no 3.3v, 2.5v, -5v, -12v rails so it stayed powered down.
But the power was still 'passing through' it. I dunno how safely though ...

As for the PC not starting when the external is off, this MAY be because it is
OFF, it is dragging the 5v and 12V too low for the main-PSU to consider it safe to start.

'Power' or 'drain' is definately passing through the GPU and causing issues
when either PSU is off. No doubts at all. Its getting through either from the
GPU power-cable, or through the PCI-X slot of the MB.


Regardless of all that, have a dig on the WWW. There are new MEGA_HIGHend PC's
out and about that come standard with two PSU's, specifically for big/dual GPU's.
You may be able to find specs on what cables THEY use to join them together.
They sure-as-hell wouldnt "manually" splice cables together, and the MB's
dont have any special plug-and-socket configurations to allow it.
Give it a try...

I may look later, depending on how far away the sandman is... he's sneaky...

It could also be this:

I also switched to a gtx570ti from an OCed 9600gt. You see the performance gain in only certain scenes. Say you have a directx 9 scene, not very complicated with a few different shaders, you get about the same fps as 9600gt. But when scene and shaders gets more complicated, you start to see the performance difference.

@EvilSOB: I think I must have misunderstood you when you talked about joining two PSUs together. Just connecting the black and green cable sounds pretty safe and has nothing to do with what I accidentally did.
I did some research on this, and there was a Youtube video demonstrating this and I found a cable that does exactly that for ~10$. But I dont want to spend that money and I dont want to wait for that cable to arrive because Im doing this because I wait for a new/repaired PSU to arrive.
I don't want to cut the cables of any of the PSUs either...

When I get home I'll first try it with the harddisk. If that doesnt work I'll try to find a way to join the PSUs without cutting any cable.



@Quad: This might be true, but still I think it is obvious that the GTX 570 won't get enough power with only 400W, so the extra power must at least do something.

(Btw, Im pretty sure there is no GTX 570 Ti. Maybe you mean a GTX 560 Ti?)

You can easily join the PSU's without 'cutting' wires.

Instead of 'cutting' them, just strip off a bit of the plastic insulation
and either twist them directly together (not so secure), or twist/solder
another piece of insulated wire between them as a bridge(better option).
Or even twist them together AND twist more (spare un-insulated) wire around
that joint for structural strength, and solder/tape it all up. (preferred solution)

That way, when you are done, just un-twist / un-solder the wires and tape over
the area where you stripped off the insulation. NEARLY as good as new, and NO cutting.

@Lukas, oops, sorry. Yeah it's a 560ti.

Another COMPLETELY cutting free way is POSSIBLE, but I dont like it.
There is some risk involved due to wires possible getting pulled out
and touching something it shouldnt while everything is turned on.
But I'll tell you anyway.

You will need a significant amount of spare insulated wire for this.
At least as heavy as the standard PSU cabling, preferably a bit heavier.


As usual, disconnect the mains cable first, to prevent un-wanted powerups.
1> Strip off 10mm (1/2 inch) of insulation from one end of each of your spare cables.
Preferred one Green and two Black, approximately 15cms(6 inches) or more.
2> Unplug your main PSU from the motherboard.
3> Now feed the exposed wires into the open end of the PSU plug, MAKING SURE no
individual strands of wire escape the hole, and that the exposed wire is fully
inside the plug, but there is still enough space around it for the original
MB pins to still go in easily. Sounds tricky, but its not really that hard.
4> Replug back into the mothrboard, being VERY careful that no exposed wire
from your joiner cables have escaped from their allocated holed.
5> Once sure of step 4> tape wires securely, double-checking 4> afterwards.
6> Strip off 10mm (1/2 inch) of insulation from the other end of each of your joiner cables.
7> Feed these wires into the end of the secondary PSU plug. If these dont feel firmly
embedded, you can strip another 10mm of insulation off and fold the exposed
wire over so it is doubled-up. Twist it up so its tight and re-insert.
8> Tape these securely in place, making sure they stay fully inserted, and that
any exposed wire is thoroughly taped over.
Done. A completely non-invasive joining of the power supplies!

Then be sure to do the same as I said before.
A> Make sure CASEs are silodly wired together.
B> Leave old HDD connected to secondary PSU.


You also have another option for step 3>, as follows.

3a> Now feed the exposed wires into the BACK end of the PSU plug, next to the
PSU's existing wires. Push them deep, MAKING SURE no individual strands of wire
escape the hole, and that the exposed wire is fully inside the plug.
If it seem a bit in-secure, you can pack in some aluminum foil to firm it up.
But make sure the foil stays 'within' the plastic. Tape these wires up before
plugging back into the MB, and double-check the wires/foil hasnt moved afterward.
If you have trouble getting the plug back onto the motherboard, it just means
one or more of the cables is packed too DEEP or too TIGHT. Look in the holes
that the MB pins go into and you may be able to spot the culprit.
Then either try to make it a bit looser with a small nail or or something,
or remove that cable and try again.
(note: dont do any of this with the plug still connected to the MB. I dont
want to push down that hard on the motherboard. Sometimes they dont like it...)


I will state again, I DO NOT CONDONE either of the above actions because the joints
as so mechanically weak. Vibrations from the PC running, heat-expansion, loose tape
are all factors that could result in a wire popping loose and causing serious damage.
I myself would use these processes for a 10-30minute test, but thats all.
But it is a purely MECHANICAL failure I would be worried about.


YOU HAVE BEEN WARNED!

Best of luck all the same.

I'm hereby letting you know that I gave up on this.

Why?
I tried the harddisk method today and I actually suceeded to boot like this. But when Windows was booted up (or rather woke up from hibernation) it said something about that the video drivers crashed and were restarted. I found that kinda odd.
Meanwhile the PSU was pretty loud (just like the ancient harddisk) and made noises I found worrying.
But as I got this far, I thought it couldn't hurt to try playing a game. So I started MW3. Shortly after it loaded, the PSU went out, and of course so did the graphic card. I guess that means that that PSU was too weak to handle only one GTX 570.

So knowing that that PSU is too weak anyway, I guess I should stop trying this and just wait until the new/repaired PSU arrives.

Thanks EvilSOB for all that advice! I really appreciate it.