ATX PSU gradually lowering voltages to my amiga when turned off!!!

[R-Typer]

Hello everyone!

I replaced my dying a500 power supply with an atx power supply and I have the following problem now when I power off the atx psu.

My ATX PSU when turned off is gradually lowering voltages to the amiga. There is a 1-2 seconds delay and during this time I can still see picture on TV and red power led on amiga is gradually loosing brightness as voltages drop slowly. This only takes about 1-2 seconds.

My powersupply is a 50euro brand new Chieftec CTG-500-80P ultra silent 14cm fan. Complies to ATX 12V 2.3 standard.

1. Will this burn my amiga as it obviously operates on lower voltages as the PSU shuts down during that 1-2 seconds time frame?

2. do you have the same problem with your amigas attached to atx power supplys?

3. which power supply do you recommend me to buy?

Many thanks!

[demolition]

This happens because the Amiga uses very little power compared to what the PSU is rated for. This means it can keep running solely from the energy stored in the capacitors of the PSU for a little.

This should not be a problem. Once the 5V rail goes below a certain threshold (think it is ~4.5V), the Amiga will hold the reset signal low (meaning activate it) to ensure it does not keep running when the voltage is too low. Otherwise it could mean instability and potential HDD trashing (instability causing invalid data to be written). This circuit is also vital to ensure proper startup so it will not start booting until the voltage is at the the proper level.

If you want to reset it by switching the PSU off and on, you just have to wait a bit longer to make sure it is completely off before switching it on again.

[R-Typer]

So I can keep using this atx psu. Great!!!

Thank you demolition!

[Xtal]

As somebody mentioned before, it's the capaciators for ripple stabilisation that is dimensioned for a lot more than supplied/needed.

One problem that can occur, is that the switching circuit in the powersupply doesn't get enough current to work properly. You may need a dummyload in form of a couple of 3.5" harddrives or something that needs both +12v and +5v. The 3.3v in most powersupplies use a stepdown regulator from either the 5v or the 12v rails.

My personal favourite is a Seventeam 230W AT (yes AT....), modded with a A1200 power supply cable. (The crappy switched A1200 powersupply is preferably exchanged with a A500 powersupply....). Works like a charm.

[R-Typer]

I have used my amiga with this atx psu and had over 60 power on/off cycles and miggy didnt fail so far. So I think Im good. Right?

Or do you think it will damage my miggy over time?

[demolition]

As long as it is a known brand, I wouldn't worry about it. The PSU should shut itself off if the output is not good enough.

The Amiga should be enough to load it so it is stable. It usually doesn't take very much. I'd say that worst case is an unstable Amiga, unless the PSU is faulty.

[R-Typer]

Thank you guys. My amiga is 100% rock solid with this atx psu. And my gaming sessions sometimes take 8 hours straight. Yaaay!!!!