Fried Mini PC - CNC build

[muxed]

Hi All,

Very much a newbie here. No Experience when it comes to electronics so i'm already preparing for a whipping.

I'm making a mach3 setup. For the most part things have gone smoothly; however I would like to include a mini PC in my control panel

Power supply is a 24V switching power supply 25Amp  240v

First mini PC i connected with a 12V Barrel jack fried instantly. The 12v barrel jack was attached to the 12v 10Amp max step down converter

Second attempt was with a Lattepanda connected microusb to USB  VIA a waveshare USB3.2-Gen1 hub.... The latte panda went up in smoke... I thought at the very least this method would work due to the countless protections the waveshare supposedly has

Is it an earthing issue or am i missing something entirely?

I've attached a picture of the setup

Thanks in advance

[DavidAlfa]

Have you verified the voltage and correct wiring polarity before plugging anything?

[ebastler]

We can't see much regarding the pinout of the main power supply, but I trust that you connected that correctly. YOur computer is only connected to the barrel jack shown in the picture and to nothing else, right?

I can't figure out where you connected the Lattepanda; I don't see any USB connectors in the picture? Was the Waveshare hub powered via the same barrel jack?

Do you have a voltmeter (multimeter) to check the voltage on the barrel jack? Is it indeed 12V as expected? Is the polarity correct? (The most likely mishap in my opinion.)

If "yes" to both, you could also measure the voltage with the multimeter set to AC Volts. There should not ba any AC component on the barrel jack, but maybe something is oscillating and giving you higher voltage peaks?

[muxed]

Hi David,

Both bucks come at +0.2V higher than rated , but assuming this is an insignificant amount?

I've checked the polarity twice over; all good.

@ebastler. I tried two methods for the waveshare, both directly wired and the barrel jack. Both seem to power the waveshare no issues. Would assume if the polarity was incorrect the waveshare would fail?

Both the barrel jack and waveshare have clear polarity indicators

[ebastler]

You didn't mention yet -- was the PC connected to anything else besides the 12V power? (Or the Lattepanda to anything besides the 5V via USB?) Either any cable connection, or maybe a ground connection via some mounting plate?

[muxed]

Hi ebastler.

Mini PC was connected to a touchscreen monitor VIA Usb + Hdmi

I dont recall for the lattepanda would lean more towards no.

Both the panda & mini PC were attached to  the galvanised mounting plate in the picture

[ebastler]

Mini PC was connected to a touchscreen monitor VIA Usb + Hdmi

I dont recall for the lattepanda would lean more towards no.

Both the panda & mini PC were attached to  the galvanised mounting plate in the picture

So there could indeed potentially be a grounding problem if the ground line from the power supply (i.e. you black wires) is at a different potential than the mounting plate, or than the ground defined by the HDMI monitor.

The first idea that comes to mind is to measure the voltage between the base plate and your black supply cable with a multimeter. However that can give misleading results: If there is no electrical connection between the two at all (which would be perfectly ok), then the multimeter would still tend to show some voltages which come from electrical noise picked up from the environment. But those voltages are harmless -- as soon as you connect some electrical load like your computer, they would collapse and disappear. Hence we need a different way to check for voltage differences:

If your multimeter happens to have a "low Z" setting, use that and measure the voltage between black wire & base plate. Is it 0V?

If you don't have a "low Z" setting, try connecting a small light bulb (12V or 24V) between black wire & base plate. Does it remain off, or do you see it glow, maybe dimly?