Floating supplies? Voltage regulator reverse short, USB and a dead UNO

[paulca]

I killed my UNO   Doesn't respond or enumerate on USB anymore.  (Well, let me just check I didn't kill my USB port!  Phew, no I didn't.)

So I was programming LEDs with this:

USB -> UNO -> ATTiny85 <- 5V Reg / 12V supply

I'd been using it loads like this without issues, but I'd been running the LEDs off a battery.  I'd measured the voltage difference between the UNO and LED circuit grounds at between 1.5 and 2.2V. 

This would partially upset the UNO from time to time when i connected the grounds, it's LED would dim but it would be fine and continue working.

Tonight I was running the LEDs off the Tenma bench supply and it was working fine. 

However at some point I cycled the power on the Tenma to uncrash the LEDs with the UNO connected.  The UNO's LEDs went out when I turned the bench supply off, which I thought was odd as the UNO was running off of USB power.

I puzzled over it for a few moments and powered the supply back on.

The UNO now no longer responds to USB.  It powers up, lights come on, but I can't tell if the MCU is functional as nothing with any indication was flashed onto it.

I can't work out if I have fried it's USB controller with floating voltages or if the reverse short of the voltage regulator has shorted the UNO out.  The ATTiny survived okay though.

The power LED dimming and going out when I depowered the LED circuit would suggest a short out.

A little baffled, but luckily they only cost a £5.

[paulca]

Output when I connect the UNO:

Code: [Select]

[ 2319.180789] usb 3-1: new full-speed USB device number 31 using xhci_hcd
[ 2319.300853] usb 3-1: device descriptor read/64, error -71
[ 2319.410795] xhci_hcd 0000:06:00.0: WARN urb submitted to disabled ep
[ 2319.410802] xhci_hcd 0000:06:00.0: WARN urb submitted to disabled ep
[ 2319.410805] xhci_hcd 0000:06:00.0: WARN urb submitted to disabled ep
[ 2319.530854] usb 3-1: device descriptor read/64, error -2
[ 2319.760799] usb 3-1: new full-speed USB device number 32 using xhci_hcd
[ 2319.880865] usb 3-1: device descriptor read/64, error -71
[ 2319.990809] xhci_hcd 0000:06:00.0: WARN urb submitted to disabled ep
[ 2319.990816] xhci_hcd 0000:06:00.0: WARN urb submitted to disabled ep
[ 2319.990820] xhci_hcd 0000:06:00.0: WARN urb submitted to disabled ep
[ 2320.110874] usb 3-1: device descriptor read/64, error -2
[ 2320.340811] usb 3-1: new full-speed USB device number 33 using xhci_hcd
[ 2320.342030] usb 3-1: Device not responding to setup address.
[ 2320.552033] usb 3-1: Device not responding to setup address.
[ 2320.760818] usb 3-1: device not accepting address 33, error -71
[ 2320.880824] usb 3-1: new full-speed USB device number 34 using xhci_hcd
[ 2320.882035] usb 3-1: Device not responding to setup address.
[ 2321.092991] usb 3-1: Device not responding to setup address.
[ 2321.300833] usb 3-1: device not accepting address 34, error -71
[ 2321.300869] usb usb3-port1: unable to enumerate USB device

Yes I have tried rebooting, different ports and cables.

The actual UNO I think is fine, the light flashes 3 times and then comes on solid.

It's the CH340 USB to serial chip that's toast   Poor thing.

[phil from seattle]

Do you have a scope?  You could see if the ch430 xtal is oscillating. (use a 100x probe).  At least it's a clone so you're not out a lot of money.

If I recall correctly, your tiny is controlling 12V. I'd look that part over carefully. 

By the way, you could replace your Uno with a Nano - super cheap. I bought 5 for $15. Frying one isn't such a loss then.

[paulca]

Yea.  I have 4 nanos    I already ordered a replacement UNO.  I find them handier for bench work.  The Nano is much better for putting into a circuit on a BB.

I have a scope, a 20Mhz one that might be challenged with measuring a 16Mhz xtal.

I am actually just about to see if the UNO still works to be programmed via Serial.

[phil from seattle]

the ch430 xtal is 12 mhz so you probably can see it on your scope.