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ATX power supply Reset/0v Issue?

Doomguy42

Member
Hi,
I'm using a brand new 300w ATX power supply. I have grounded the Green reset wire to one of the ATX 0v wires. On powering up the supply doesn't always reset/switch on. If it's not switched on if I break the Green wire/0v connection and touch it back together it always switches on. So it seems to stick. Is there anything I can do to help this eg a resistor?

I suspect the reason for this happening might be that there's 1.5v bleeding onto the 5v rail with the supply off. So the green reset wire and 0v might not be relative to how they should be?

What it is, is a twin cabinet arcade game. The left side (master) had this ATX set up fitted by myself a few years ago and works perfectly. The old original power supply died in player 2 right side (slave) recently. I've fitted the same set up only I have this sticky reset issue. The power rails do not link between games, the networking is optical, however there are some shared boards where I think the 1.5v bleed is coming from. The whole set up works perfectly I just need to jam this power supply on.

I've given the ATX power supply's both independent mains which has helped and its less frequent. It's no longer powered as a master/slave through a shared step down transformer.
Any ideas on what to do next?

Thanks
 
OK yes, the green wire Pin 14 on an older 20 pin PSU is PWR_ON and Pin 16 on newer 24 pin supplies. Some supplies want to see a load on the 5.0 volt bus so I normally used a 10 Ohm 10 Watt resistor on the 5.0 volt bus.

The green wire (PWR_ON) should show 5.0 volts to ground held high by an internal pull up before grounding it. The 5.0 volts is from the SB (Stand By) PSU supply. The only reason I can think of is if you are not using the 5.0 Vout it may need a load as I mentioned or the 5.0 volt PS_ON is not a stable ground.

Ron
 
Hi Ron, thanks very much for the reply. There's a good load on the 5v bus, it's powering the game PCB stack, but it is potentially at 1.5v on powering on (shared boards, audio boards etc. I can measure 1.5v with the power supply off. Do you think that's canceling the load? Is there anything I can do while still keeping the 5v bus functioning normally?

Thanks
 
With the PSU Off you should see 5.0 volts between the PS_ON (Green Wire) and ground (any black wire. That 5.0 volts is from the 5.0 volt SB (Stand By) of the PSU. Where are you seeing 1.5 volts? That is peculiar. You may also wish to measure those same points on your working unit.

Ron
 
I've included a pic of the system. The ATX power supply is just for the righthand main logic PCB stack . There are other supplys for AMPs, feed back devices etc. The two games share some common middle boards. The 1.5v on the main 5v rail could be coming from anywhere.
The issue seems to be there from a hot restart. I think it must be the load it needs getting effected by the +1.5 volts?
I will measure the standby voltage thanks for the replies. Appreciate its unusual.
 

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  • 20240612_121151.jpg
    20240612_121151.jpg
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Yes, you should be seeing 5.0 volts on the green wire and ground. Strange?

Ron
 
Grounding of the green wire (PS_ON) to the 0V (ground) line should be solid and not loose. Sometimes, a poor connection can cause unreliable behavior.
 
This may help you .. .. in 2015, slightly more of a novice EE than I am now, I built this ..
ATX 1.JPG
ATX 6.JPG


.. .. .. a bench PSU based on a plan I found on the net which is also attached.

The 2 Green LED's provide a static load, the Red LED confirms Mains Power, and the switch shorts the green wire to ground which provides an output. The 'System OK' is from the 5v TTL check circuit via a 548B transistor.

MM
 

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