Voltage in off state

[Neal]

Hello,

I just hooked up my ATXraspi R2 to my pi as instructed in the tutorial. I'm getting power to the pi, even though I have not triggered the button. I am not getting the full 5 volts, but instead around 1.25 volts when the pi is supposed to be off.
Turning on the pi by triggering the button works as expected, supplying a full 5 volts. Whenever the circuit is off, I still get a residual voltage that is enough to make the pi's power LED light up.

Thanks in advance

[Felix]

That's not normal. ATXRaspi switches the +5v, so unless you got something on your Pi that sinks current back into ATXRaspi, it should not do that by itself.
I've seen it in other cases where folks had stuff attached to the Pi which could sink or source current...
I noticed some routers (CAT5) will cause such weirdness...

So I guess my first question is what do you have attached to your Pi? (including HDMI, network).

[Neal]

Right now, I've got an analog monitor, a USB hub and speakers hooked up to it. I have no network hooked up to it.

I am using the pi for an embedded system so I am wiring power directly from ATXraspi to the pi (bypassing the micro-usb socket), soldered at the t1/t2 holes. I am supplying power to the ATXraspi (and to the pi) through a 12v, 2A power source, converted to 5v, 1A by a switching regulator. The strange thing is, the issue is only present when using the 5 volt differential from the regulator (I've checked that there is a 5-volt difference across the ATXraspi power input sockets). When I supply power from a micro-usb wall charger there is no voltage across the pi terminals when off, as it should be. I haven't had a lot of time to look over this, but at the moment I have no clue why I would be getting different behavior. They should be the same, as the + terminal on the micro-usb and solder socket are the same connection (Right?). The regulator outputs a little below 5 volts, at 4.98, while the wall charger outputs at a steady 5.02.

The reason I am using the 12 volt power supply is to also power the analog LCD screen hooked up to the pi. I have an NPN transistor acting as a switch, so when ATXraspi is activated, it also turns on the monitor. I have checked the circuit without the monitor switch, and the problem persists.

Hopefully this is a little more information about my situation.

Thanks for the help

[Felix]

There is probably a difference in the power supplies. One might be isolated, one might not. One possible issue is that the switching supply might produce a ground that is floating slightly above or below mains ground, causing a ground loop, not enough to cause smoke, but enough to light LEDs.
Is the USB hub powered separately? Anything that goes to another supply or attached in any way to mains? Those supplies could also have this issue, it's not uncommon with non-isolated supplies.
This is something i've personally seen before, but I guess it could be something else, but since the other 5V charger works fine, I suspect it's something with the 12V supply... not sure what else it could be.
The + on the GPIO is not going through the PI's fuse. I don't know if there are other differences but that should not be a big deal.

4.98 vs 5.02 is also no big deal, as this gets regulated further by the Pi to 3.3v.