Powering a older PC with a bench PSU (For fun)

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Hello,

I have an older computer that is not that important if I blow up royally so I wanted to hook it up to a bench power supply for fun to see if I can actually get it to power on. Problem is there are three connectors in a stranded 20-pin ATX connector that confuses me, take a look at the following diagram,



Pin 9 confuses me a bit, how is +5 VSB different from just regular 5 volts? Furthermore, my bench power supply is one I built from an ATX PSU so I know its semi beefy and can handle a good amount of amps but something I did not add was negative voltage. This leads to a problem with pin 12 and pin 18 or -12 and -5 volt respectively. What is a good voltage inverter circuit that I can build that would allow me to convert my +5 and +12 voltage lines to negative? The ones I find online do convert to a negative voltage but they either don't output a whole 12v or they drop in voltage upon load. Does anyone know of a good voltage inverter circuit that cleanly converts +12 to -12 volts?

I built this last night but it divides the voltage so I would need 24 volts to create 12 volts and my bench power supply which is just a converted ATX power supply anyway only goes up to 12 volts. The computer I am powering I can't imagine takes many amps, its like a 133 mhz, I'll probably throw it away after this. I don't even think its Intel, its that generic Intel clone, Cyrix or whatever. I don't mind keeping older computers but when a $10 computer from today out perform something, I see no reason to keep it.

Thanks, look forward to you guys suggestions.

Two thoughts:
1. Wouldn't the simplest solution simply be to reconnect to the needed solder pads on the ATX pcb?
2. I loved my Cyrix back in the day. IIR, there were a number of registers that could be set via software to enable enhancements that really made it a fun chip to run.

I actually avoided replying to this because I think I am having an aspie moment, I am not following this. If you are referring to the ATX connector from the PSU, I think I have thrown that away and all the cables from the PSU have been cut to be used in other projects. If you are referring to the ATX connector on the motherboard, that is completely untouched right now. The issue is, the ATX PSU cables have been replaced with five binding post (Ground x2, 3.3v, 5v, 12v) effectively making it a bench PSU. I couldn't return the PSU back to its original state as all of the cables have been removed on the chip level and I don't even remember which connector is what anyway. I took pictures before gutting the PSU but I don't know what I did with them.

Here is picture of the PSU, it doesn't even resemble a ATX power supply now,



I found this, and it appears to support a load up to one amp which is more than enough for the board. This leads me to believe the -5 and -12 volt lines aren't that important but I still need to know how +5 VSB is different than regular +5 volts.

I actually don't think I can do this, the PSU list +5 VSB as a completely separate line with separate current, I might need to open the power supply up and re-solder that line and I am unwilling to do that. Too much work, I can just emulate anything that'll run on a Cyrix.

Resoldering a line to the correct solder pad on the ATX pcb is what I was referring to - and you are stating that you don't want to do that. I agree it would be a lot of trouble considering how nice the PSU case looks, and doing so would modify the bench supply away from what you want/need it to be.

However, that line (VSB) is just the "Stand By" +5 volt line. It delivers +5 when the PC is off and 0v when the PC is on. The +5 is just so the motherboard can send +5 to the PSU when you press the soft "power button" that would normally be on the front of the case. Also, I'm guessing you had to modify it on the PSU end during the bench supply conversion anyway so the PSU would turn on?

Which Cyrix is it and what were you planning on running on it, anyway?

I loosely followed this guide.

However since the PSU has a switch on the back and some older PSU like the one used above didn't, I didn't bother to use +5 VSB or LEDs at all. 5v and ground has a 10 ohm / 10 Watt resistor between them to simulate a load and thats it on my model though rereading that howto and your reply, I believe I have a better understanding of what +5 VSB is.



So I don't need the +5 VSB at all as long as the PSU has a simulated load to power on, correct?



I think its a Cyrix 6x86L 133MHz, whatever it is I know its 133 Mhz.

I didn't plan on running anything on it really, I was really just bored and was looking for a project and a voltage inverter circuit sounded fun to do. I wasn't even planning on keeping the chip but some people are selling em on ebay for about $20-30 bucks so if I can test it and make sure it works, I might sell it. I can't test it any other way though cause I don't have an extra power supply.

You are correct; as long as the PSU is controllable via other means, you do not need the +5 sbv. I do wonder though, if you will need to sink to ground the signal line from the motherboard that would normally send that +5 to the PSU to tell it to turn on?