Author Topic: Odd ATXRaspi R3 behavior with a regulated switching power supply (cheap)  (Read 504 times)

gerryb

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I recently completed a project incorporating an ATXRaspi R3 with a Pi-zero.   While developing the project I used a DIY bench power supply which I put together from a PC power supply.   Using this PS, I've had no problems with the ATXRaspi at all - it worked as expected.   I was initially using the latching LED pushbutton from LowPowerLabs.

The project takes 12VDC, goes through a MOSFET being used as reverse polarity protection, then bucks the 12V down to 5V which goes into the ATXRaspi.

The person I built this for provided his own 12V power supply.   It is a S-120-12 Regulated Switching Power Supply.  When I demonstrated the project everything seemed to be working fine.   The next day he used the project for about 4 hours straight (just one startup/on shutdown).   The day after he called indicating the project was not shutting down as I described it should.   The LED on the button would not stop blinking on shutdown and he didn't know whether it was safe to shut down power (controlled by an external SPST switch).   

I retrieved the project and took it home to investigate.   Using my power supply, I could not duplicate the problem.   I took the project back and could readily reproduce the problem.   I took it back home again, thinking it was an intermittent problem somehow and I just didn't produce the right conditions to exhibit it.  I checked for loose connections, bad solder joints, broken wires and found none.  Just to be sure, I unsoldered the header pins on the power btn and LED through holes.   Again, worked perfectly at home.    Took it back, same problem.   With the only difference being the power supply, we tried a different one.  He happened to have a 12V battery and a 12V brick PS.  With each of those the project worked fine, but would fail with the previously used PS.

The behavior with the "bad" PS was the ATXRaspi powering up WITHOUT turning on the pushbutton switch.   Once the PI came up and asserted BOOT OK, SHUTDOWN would be immediately be asserted and the PI would shutdown.  Instead of shutting down, it would reboot and the cycle would continue.   The button LED was never really solidly on.   It flickered.   Actually after the second  shutdown, instead of pulsing slowly, it would blink 3 times very fast, pause and repeat until the pi was done shutting down.  The fact that the ATXRaspi powered on when the button was in the off position made me think there was some kind of short in the button/led header, which is why I desoldered/resoldered.

While trying to diagnose the problem, I did take measurements of voltage.   The values were all in the expected range.   The voltage at the ATXRaspi was 5.1V.   

So, given that everything works with my bench PS, the battery and the 12V brick, I'm convinced there's nothing wrong with the ATXRaspi (or perhaps it *is* damaged somehow, but the damage is only evident with that PS).

Does anyone have ideas as to what might be causing this behavior?    I don't have access to an oscilliscope, and even if I did, I don't know what I'd be looking for.   But I'd suspect the power coming out of the PS is "dirty" and is somehow fooling the ATXRaspi into powering the pi even when the switch is off.    Thoughts welcome.


Felix

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Re: Odd ATXRaspi R3 behavior with a regulated switching power supply (cheap)
« Reply #1 on: September 21, 2020, 09:21:45 AM »
Is it a ATXRaspi R3 (or does it have the 5 pin top header)?
Try tying that to GND instead of leaving it floating. Let's see if that changes anything.

gerryb

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Re: Odd ATXRaspi R3 behavior with a regulated switching power supply (cheap)
« Reply #2 on: September 21, 2020, 01:23:01 PM »
Thank you for your response.

Yes, it is an R3.    I'll give it a try (may be a few days though).     Any idea why it would be a problem with one PS and not the other?   Or it's just chance?


Felix

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Re: Odd ATXRaspi R3 behavior with a regulated switching power supply (cheap)
« Reply #3 on: September 21, 2020, 01:25:11 PM »
Wild guess - maybe noise / different environment.

gerryb

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Re: Odd ATXRaspi R3 behavior with a regulated switching power supply (cheap)
« Reply #4 on: September 25, 2020, 05:14:18 PM »
Grounding the SoftBtn had no effect.  The ATXRaspi powered up the pizero immediately.

The wiring from the ATXRaspi to the toggle switch was checked.  No continuity was observed when the switch was off.  Continuity was established when the switch was on.

When the leads from the switch switch were disconnected from the ATXRaspi, the Pi would not be powered on.   As soon as switch was connected (in the OFF state), the Pi would power up.   As soon as BOOTOK was asserted by the Pi, SHUTDOWN would be asserted by the ATXRaspi.

One very interesting observation - when either lead from the switch was connected to the pin next to the SoftBtn thru hole, the Pi would power up.   And actually if one of the leads from the switch was touched to the SoftBtn thru hole, the pi would power up.  Note: the other switch lead was not connected to anything.   When one of the switch leads were connected to pin next to the inside LED pin, the pi would not power up.

Anything else you can think of?    Again, I appreciate you taking the time to reply.

 

Felix

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Re: Odd ATXRaspi R3 behavior with a regulated switching power supply (cheap)
« Reply #5 on: September 25, 2020, 05:48:17 PM »
What happens if you power the ATXRaspi without the Pi attached?
Try with the button attached, or without (just short the BTN pins to simulate a "button press").
Then simulate the Pi booting up successfully connect the BOOTOK to one of the 5V output. The BOOTOK LED should now come on, without any other effects.

gerryb

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Re: Odd ATXRaspi R3 behavior with a regulated switching power supply (cheap)
« Reply #6 on: September 25, 2020, 06:58:08 PM »
With the Pi disconnected and the switch OFF,  when power is applied, the ATXRaspi's switch LED comes on flashing very quickly (like there's a loose connection - not like right before the ATXRaspi shutsdown).   When 5V is applied to the BOOTOK,  the BOOTOK LED comes on, followed immediately by the SHUTDOWN LED.    When the 5V is removed, the LED starts blinking slowly.   Then the SHUTDOWN LED turns off but the switch LED starts flashing quickly again and never turns off until all power is removed. 

Repeated the process.   But before applying 5V to BOOTOK, turned the switch ON.  Switch LED went solid.  Turned the switch off, then the SHUTDOWN LED came on only momentarily.    When 5V was removed, the Switch LED blinked rapidly but never turned off until power was removed.


Felix

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Re: Odd ATXRaspi R3 behavior with a regulated switching power supply (cheap)
« Reply #7 on: September 28, 2020, 03:40:49 PM »
Can you provide a photo that clearly shows how everything is wired?

You say "with switch OFF". But the switch is a momentary button right? It's always off, unless you press it as a means to tell ATXRaspi what to do. Unless it's a latching button, in which case the ATXRaspi has to be configured (via jumpers) to function with a latching button.