G3 Beige Minitower ATX Sanity Check

[klgroves]

Hello all,

I recently pulled an old Beige G3 Minitower out of the basement to try to get it up and running again. After dusting it off I powered it up and out popped a non-bootable floppy that I guess had been left in it, and then it booted up into OS9.2 just long enough to give a few errors about the hardware clock and then suddenly all power went off. There was no fan, no lights, no voltage on Pin 9 TRKL. So I pulled the PSU and tried to jump it with the green wire with no effect. I'm assuming the PSU is dead and I will try to replace it with an ATX.

I have an Earthwatts EA-380 new in box which is 150X86X140 mm with a rear fan that I plan to use. I replaced the PRAM battery. I bought a 24 to 20 pin adapter cable which I plan to modify fit the Minitower. I read that I will need to change pins 8 and 18, so I had planned to re-pin the pins 8 and 18 of the 20 pin connector with the orange +3.3 V and black Ground wires from the +4 cable, respectively. The motherboard jumper is already set to PS/2.

I just wanted to check on an active forum whether this is correct for the Minitower, particularly whether pin 8 really needs to be 3.3 V for the Minitower, as there is some conflicting information out there. Is there anything else I would need to do? Anything to watch out for?

Thanks,

Kevin

 

[Phipli]

I bought a 24 to 20 pin adapter cable which I plan to modify fit the Minitower. I read that I will need to change pins 8 and 18, so I had planned to re-pin the pins 8 and 18 of the 20 pin connector with the orange +3.3 V and black Ground wires from the +4 cable, respectively. The motherboard jumper is already set to PS/2.

With the jumper set to PS2, you don't actually need to rewire the cable. Just plug it in.

Sadly the internet is full of misinformation.

 

[Phipli]

The big issue with ATX conversions is airflow - the stock PSU is cooling the case, so you need to make sure you keep the case cooled appropriately with your new solution.

 

[MrFahrenheit]

I can confirm with Phipli and agree with the jumper and cooling issue. Change the jumper and you’re good to to as-is.

 

[Phipli]

Change the jumper and you’re good to to as-is.

Not quite, the jumper is already set correctly to ATX on towers...

Yes, it is insane that towers and desktops had different PSU setups.

 

[klgroves]

Ok, thanks, I had a feeling that was the case, but this post was rather explicit about the need to do this for the Minitower. Some other guy on Reddit 6 years ago or so claimed to have "blown up" his beige G3 by not doing it, though that didn't sound very credible. That said, the wire colors on the original PSU in the Minitower seem to be standard ATX, although there is some kind of connection between the grey wire to pin 8 and the adjacent black ground on pin 7 wrapped under shrink wrap.

I will give it a shot and see how things go.

 

[Phipli]

Ok, thanks, I had a feeling that was the case, but this post was rather explicit about the need to do this for the Minitower. Some other guy on Reddit 6 years ago or so claimed to have "blown up" his beige G3 by not doing it, though that didn't sound very credible. That said, the wire colors on the original PSU in the Minitower seem to be standard ATX, although there is some kind of connection between the grey wire to pin 8 and the adjacent black ground on pin 7 wrapped under shrink wrap.

I will give it a shot and see how things go.

I have done it myself a few months back, plus, earlier today I checked the continuity between PWROK and 3.3v and confirmed that isn't an issue.

Modern ATX PSUs don't have -12...

I was confused by those posts until I sat down and reassured myself, then tested it.

 

[NJRoadfan]

Modern ATX power supplies don't have -5V rails, the -12V is still there. The bigger issue is that the +5V rail on modern units may not supply enough amperage since modern systems pull most all their power from the +12V rail and regulate it down on the motherboard. I am running an ATX power supply in my Beige G3 tower without a problem. Just set the jumper to PS2 and it worked fine.

On a side note, I just pulled on of those 380W EarthWatts units from my parent's machine. It had problems with the 5VSB rail not supplying enough power to turn on the system. This is the second Antec power supply from that era I've had the problem with. I think these are OEMed Seasonic units. Not a bad power supply, but they are suffering from age related problems as they are 15+ years old in many cases.

 

[croissantking]

The big issue with ATX conversions is airflow - the stock PSU is cooling the case, so you need to make sure you keep the case cooled appropriately with your new solution.

I always thought it was just the DT which does this. The MT has, additionally, a large (120mm?) chassis fan.

 

[Phipli]

I always thought it was just the DT which does this. The MT has, additionally, a large (120mm?) chassis fan.

And a fan in the PSU?

Removing 50% of the fans in a computer isn't a good idea.

 

[klgroves]

The PSU I plan to put in has a rear facing fan. Is the concern that it will throttle it down at low output and be insufficient to cool the case? What if I bypass the internal temperature sensor in the PSU so the fan is on full all the time?

 

[Phipli]

Is the concern that it will throttle it down at low output and be insufficient to cool the case?

This can be an issue. Another thing is to make sure the fan is pointing in the same direction (inlet I believe in these), as the stock one, otherwise the two fans are fighting each other and you get odd airflow behaviour including potentially no air movement in the middle between them. A third is that the other opening in the PSU isn't blocked by case metalwork.

 

[croissantking]

And a fan in the PSU?

Removing 50% of the fans in a computer isn't a good idea.

Doesn't it blow out the back of the machine on the MT, the same way as any other ATX PSU?

 

[Phipli]

Doesn't it blow out the back of the machine on the MT, the same way as any other ATX PSU?

I'm probably wrong. I don't have one set up.

But make sure it is checked before doing. Fighting fans can result in zero cooling at a random location.

 

[klgroves]

Success! Thank you all for the responses, it worked perfectly without any modification of the ATX connector as suggested. While in there I replaced the main fan with a 120 mm Arctic P12 and there is good air flow coming out and the PSU is also blowing out the rear, allowing intake along the side panel. The previous owner swapped the original G3 233 MHz for a 500 MHz, so I hope this is sufficient. I will keep an eye on it for now.

Thanks, again. I'll probably have more questions as my 800k/400k disk imaging project gets going...