ATX supply question

[KI6PMN]

I had this problem a long time ago one an ATX power supply I converted over. It turned out, if I remember correctly from memory that there was a capacitor that would cause the delay, once it would discharge it would "restart". Of course this only happened once the mains supply was removed as the power supply, although shut down still remained active in that part of the circuit.

[KA9JLM]

Not sure what brand or model number you are working with, but some of the supplies rely on the 6 or 8 1200uf caps that are on a Motherboard to be on the 5V red connections.

I have seen power supplies fail to start when the Motherboard caps go bad. The 1200uf 6.3V that normally fail.

5 volts is normally always on for wake on lan and the front push button.

You may try to add some caps outboard to the power supply 5 volt line and see if that may help.

Many motherboards have a total of 7200uf and that power supply may rely on them to work properly.

There are some on the 12V also, but I don't think that would keep the power supply from at least trying to start up, it would try to start then shut down after a second of so.


How do you have "Power Good" connected ?

[K8ERV]

I have 5 ohms from +5 to gnd, and the power turn on link shorted.

TOM K8ERV Montrose Colo

[WA9SVD]

I converted an ATX to a general bench supply. Very easy, and works well. But when I overload it (brief short etc) it shuts down.

Ok, but in about 30 minutes? it comes back to work.

I can't figure out what kind of protective system it uses that takes that long to reset.

Any ideas?

TOM K8ERV Montrose Colo

The "power on" signal for ATX supplies is normally a momentary contact switch to the motherboard. it's handled by (il)logic from there. You may have to break that contact as well to get the supply to "reset" in a reasonable amount of time. the "long time constant" you describe points to a relatively large value capacitor in the turn-on circuit that needs to be discharged either through time or some other means before the supply can "come back to life."

[K8ERV]

That's a good thot, will try it when I get it apart. Not real high on my priority list.

That and the freeze mist test.

Sure is nice to have a light 10-amp supply instead of a small car battery.

TOM K8ERV Montrose Colo

[KH2G]

Probably a bleed resistor open in the circuit so your waiting for a cap to discharge to the reset point.
Regards
Dick

[K8ERV]

I'm going to check the cap voltages. Not a high priority item, but hope to find the cause.

TOM K8ERV Montrose Colo

[K8ERV]

I want to thank all who have made suggestions. If all else fails I will try a different supply, I have a lot of them.

I am just trying to learn something.

Hard to do when you already know it all-----------

TOM K8ERV Montrose Colo

[AF6LJ]

I want to thank all who have made suggestions. If all else fails I will try a different supply, I have a lot of them.

I am just trying to learn something.

Hard to do when you already know it all-----------

TOM K8ERV Montrose Colo

Yah I know

[KA9JLM]

I'm going to check the cap voltages. Not a high priority item, but hope to find the cause.

TOM K8ERV Montrose Colo

It may be the Flux Capacitor that is not getting discharged.