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RE: more power questions













Play-mate,

First, congrats on your Christmas gift! That's a fine gift... I wish I could convince my wife I needed something like that... maybe a new SSD?

Also, thanks for your report on implementing a separate supply for the HDD. That's part of the standard cMP setup, but I don't recall anyone reporting a sonic improvement from doing that... glad to have more evidence.

On your questions, first about what you risk when you swap in a new PSU... As long as you can confirm that your supply is working as it should, you are good.

But how do you do that? Here's what I do:

1st - validate the +12v out of the raw supply using a meter... doesn't have to be anything fancy.

2nd - hook up the PicoPSU to the +12v & validate it's operation with a computer power supply checker. I've attached pictures of the two I've used... the simpler one was the first I had and it just lights an LED to show that the supply is operating. The fancier one validates all the voltages and checks the delay time between initiation of power-up by pulling the PS_ON# pin (#14 on an ATX-20, #16 on an ATX-24) to ground and the supply signaling it is up and ready by putting +5v on the POWER_OK pin (#8) (see attached pin-out too).

BTW, the simpler one is branded Antec and cost me about $10 5-6 years ago, the fancy one cost about $25 early last year... I'll try to find where I got it from and post it later. If you are planning to ever do a DIY fully-linear supply, then I recommend the fancy type... otherwise the simpler type is ok.

Once you get a good result using one of these, you should be ready to power-up. BUT, I would make sure you have backed-up your settings using the BIOs facility for doing so and I would recommend backing off on the under-volting for the first test... say taking it up a 1/2 volt or so.

As for grounding, there shouldn't be any issues. Your 12v supply to the PicoPSU is grounded to the motherboard through the Pico and if you have a separate supply for the P4 +12v, it is also grounded via two of the P4 pins.

Finally, I also saw your question via email earlier today and thought I'd answer it here too...

Your separate computer SMPS for the P4 was getting it's turnon signal from the motherboard via the PS_ON# pin being pulled to ground. You can fake this by running a jumper between the PS_ON# pin (#14 on an ATX-20, #16 on an ATX-24) and one of the ground pins next to it on the ATX-20/24 connector... this is how the simpler power supply checker I have does it.

This should solve your issue with that supply.

You also mentioned the PWR pins on the motherboard. On most motherboards I've seen, there are two sets of power pins... one for the power switch, one for the power LED. You do need to have a momentary-contact SPST switch connected to the power switch pins, such as the power switch on your case. (BTW, polarity is not important, when testing power supplies with motherboards, I generally have them laying out on my workbench & just bridge these with a screwdriver or pair of needle-nose pliers).

The power LED is only an indicator and does not affect the turn-on sequencing.

Take care!

Greg in Mississippi
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