Post Burn - Pixelblaze V3 Standard won't power on at all

[Pugworthy]

I had a Pb V3 powered large fuzzy cat tail at this years burn, which was great until “that weather” showed up. I disconnected from power and parked under some shelter when the rains started. I never did try running it again until now.

Problem is, the board doesn’t seem to be powering on at all now - no on-board LED lighting up at all with no LEDs hooked up and just using USB for power. I had it it a 3D printed case and there’s no obvious physical damage or signs of crust, dust, or water.

Any thoughts? It makes demoing at work a little hard, plus I have to explain why I have a 5’ long 8-9" diameter furry cat tail at my desk that won’t light up.

[ZacharyRD]

Have you tried powering it via the contacts on the board itself, versus USB? Micro-USB connectors are always iffy and the first thing to break on all electronics like this — try running 5V power in at the screw terminal block (if you have it soldered on) or via alligator clips if you don’t.

If you don’t have a power supply for this, FYI you can carefully cut apart a USB cable to get a bare 5v power and ground wire from it, although they’re a bit thin and fragile for long term use.

I’d assume from your story the USB connector on the board is dead but not the board itself.

(Also have you tried swapping to a different USB cable and power supply?)

[wizard]

If you have access to a multi meter, check that the VIN and GND isnt shorted, you are seeing 5V on the pins, on the pad underside, and 3.3V on the 3v pad.

I’ve seen the mosfet short out when zapped with ESD, and the USB port burn out due to that as well.

[Pugworthy]

Ok I got a chance to go into the lab and do some testing.

First, no boot on either usb or 5v fed into the LED screw terminals, so not a USB issue.

Second, there is continuity between power and ground, so it does sound like the mosfet issue mentioned.

Not really sure when it would have died unless a lot of people were petting the cat tail without consent and causing static

Can the mosfet be desoldered and replaced? I’m comfortable with the action if you can give me the part spec.

edit

This one?
https://www.mouser.com/ProductDetail/STMicroelectronics/LDL1117S50R

Also on close examination there is some visible damage on the part

[wizard]

Hi @Pugworthy ,
Yep, I think definitely the mosfet fried and is shorting the power.

Another thing to check if your USB power source might have output more than 2A into the short. Most USB power packs and spec compliant USB ports have short protection. Ideally the USB power source would cut out when the current draw exceeds normal USB ranges. If it doesn’t, it can cook the USB connector which is only rated for 1.8A (but often works fine to 3A or so) and/or the USB cable.

Yes you can either replace the mosfet with another P channel mosfet, or remove it and bridge the power path with a bit of wire. If you remove the mosfet you lose reverse polarity protection, but the rest of the components on the PB should tolerate a great deal of ESD without problem.

If you replace the mosfet, use one with a max gate voltage suitable for your voltage input range (20V for the one I use) and a fairly decent current rating. I use the AO3407.

You may also want to consider using some clothing anti static / anti cling spray on the fur.

When I cooked my PB with my fur coat, I was shooting sparks over 1", and quite painful ones at that. I ended up bypassing the mosfet, but also spraying anti cling throughout it so I wasn’t constantly getting zapped myself.

This is the mosfet on the PCB, just above the bottom mounting hole. Its to the right of the “DAT” printed on the board:

You’d bridge the top left (pin 2) and bottom pin (pin 3), leaving the top right (GND) alone.

---

edit

The 5V LDO, yes LDL1117S50R, is there for over-voltage protection. If you see damage to that part it I’d replace it, but it’s a bit odd, I haven’t see one of those blow up yet, but might happen if seriously over volted.

[Pugworthy]

@wizard

The 5V LDO, yes LDL1117S50R, is there for over-voltage protection. If you see damage to that part it I’d replace it, but it’s a bit odd, I haven’t see one of those blow up yet, but might happen if seriously over volted.

It took me a bit to realize we were talking about different parts. I was mixing up the LDO and the MOSFET. Also I discovered the dark spot on the LDO actually scraped off so wasn’t the damage I thought it was.

Not sure how it could have gotten an over voltage, as I used a USB power bank to run the setup. It was on a QC3.0 output port on the power bank. Ran without issues for maybe 6-7 hours total.

I will try just bypassing the MOSFET to diagnose and see if that fixes the issue.