ATX PSU question

[Davespice]

Hi folks

I am using an ATX PSU to drive a minigun supergun that I built via this little breakout board. It works well for small boards like the famous 60 in 1 or a Neo Geo MVS 1C but for some larger boards, like an SF2 bootleg it seems that the measurement reported by the voltmeter stays too low (around 4.43 VDC). I thought that an ATX PSU has a means to auto-sense when more power is needed and deliver more power in real time. I have seen the PSU adjust downwards from above 5.0 VDC but seemingly not upwards from below it.

Am I missing something here?
Many thanks for any pointers

Dave

 

[sukhbir]

As the +5volt pushes out more juice you need a thicker gauge wire especially when you connect to larger pcbs as they're power hungry.

 

[Davespice]

I am not sure that is the problem, you would expect that the wires would be getting warm if I was reaching the limit of current that could be delivered through them right? They certainly were not getting warm. I can always try it again with thicker wires though.

 

[Retroman839]

Maybe the bootleg needs more than the ATX can give ?

Do ATX 5v go to 5.5 or more ?

I have a street fighter boot only the sound wouldn’t work..
But then sound worked at 5.5v. With a arcade psu though not ATX.

I put it down to bad caps for the 5.5v as soon as a week later no sound at all.
( still need to recap it)

Do you have any other way to power the bootleg to Clarify it works ?

 

[Davespice]

Hi there, sorry for slow reply on this. Yes the SF2 bootleg has no issues, works fine with a standard arcade PSU with the voltage turned up so the Supergun reads 5.0V.

 

[Fantazia2]

What ATX PSU are you using, have you checked what it will output on the 5v rail in terms of amps? It should be printed on the side could be that its just not up to the job of powering the board unlike the standard arcade PSU.

 

[Davespice]

It's this 600 watt one; https://www.amazon.nl/dp/B085GFBH39/
Max current on 5V is 20A

 

[Bods]

I had a Jamma cab that wouldn't power some bootleg boards but an old table cab would, main issue was no 5v Adjustment on the Jamma cab PSU as it was built into the monitor chassis, table had standard jamma cab type psu with adjustable 5v which I had to set over 5v to stop Graphics issues on Final Crash (Final Fight) Bootleg so low 5v is more than likely the problem as you'll need 5.1v probably

 

[Davespice]

Thanks for all the advice everyone, but I think we're drifting away from my original question. Which is more about whether an ATX PSU auto-senses the 5V line dropping and provides more power to compensate, surely this must happen in a gaming PC when you open a game which draws loads of power from the graphics card right? I always thought PC PSUs self-regulate. Looking at this page there is a nice graphic about half way down showing that there is sometimes present a +5 sense line. I need to check if my PSU has this and which pin it actually is on. I am also wondering whether it is possible to connect the 5V rail to the 3.3 sense rail via a voltage divider (e.g. R1=50, R2=100). There must be someone on here who's played with this?

 

[Bods]

The problem is you need PSU with adjustable 5V so you can set it over 5V as 5V or less on some bootlegs isn't enough, doesn't matter about amps/watts it's the voltage and auto sensing ATX won't set it self to 5.1v +

 

[TheDaddy]

Answer :- Dont use a PC power supply !!!!

Get a decent Suzo Happ one.

Dave.

 

[sukhbir]

Yeah you need a proper arcade switch mode power supply with +5v adjustable.

 

[Georgian2]

I did add an pot to an atx power supply. You need to trace the IC that regulates the 5V and find the FB pin and trace its resistors. After thet check the datasheet and calculate whatbresitor you need.

 

[Georgian2]

It works well for small boards like the famous 60 in 1 or a Neo Geo MVS 1C but for some larger boards, like an SF2 bootleg it seems that the measurement reported by the voltmeter stays too low (around 4.43 VDC). I thought that an ATX PSU has a means to auto-sense when more power is needed and deliver more power in real time.

It dose have an autosense but it is connected inside the PSU.
With that thin wires connected, there is no way it can work. The problem here is the CPU and other parts need more current on short periods of time and that thin wires won't keep up.