Duet Wifi 5VDC Protection
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So a while back I got a duet wifi clone (don't hate me, I am only just getting into 3d printing and didn't want to jump in too deep off the get-go) and while installing my bl touch did something stupid and shorted the 5VDC to GND on the expansion board.
What I'm not clear at is if there is any fusing that would have protected the 5V converter chip normally (when I looked at the installed fuses they are wildly oversized, I have some properly sized ones that I'll install, and the board still works using USB power). I am in the electrical design field so I'm usually pretty proficient with schematics, but PCB schematics as used in the github repository are a little tricky for me to follow.
Basically I'm wondering if the clone using correct fusing would have changed anything, or if there is no protection in the 5V circuit in the event of a short to ground.
Again, it's a cloned board so don't feel the need to answer if you don't want to, just curious if I should try and get a replacement board out of them or just take my medicine (seriously it's my day job to work around this stuff, it's a little embarrassing to make such a rookie error...) it is real nice that the design allows for external 5VDC input, and I'll be utilizing that once I locate a good
sacrificecandidate power supply from my assorted odds and ends. -
Sounds like the 5v regulator got blown. I don't know what fuses you're talking about since it's a clone I have no idea what they put where. A photo of what you mean might help.
Even on a genuine board I don't know if there would be much protection against that either.
Are you sure you just shorted 5v to ground?
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U3 chip definitely got smoked. The fuses I'm referring to are the mini-blade 1A, 7.5A, and15A fuses, the clone I got shipped with 10A, 15A and 30A instead, but looking at the schematics they all seem to be on the 24V side so likely wouldn't have saved the U3 chip. Currently I have moved the 5V jumper to the external source position and like I said am powering the board via the USB input and a Samsung USB wall charger.
I'm pretty sure it was 5V to ground that did it? I was being a dumb-ass and installing the bl touch while the board was energized, and (stupidly) didn't insulate/tape up the pins while doing so. it was a bit of a shit show initially, I had the ground in the right most 3 pin connector that came with the bl touch, and the wire that should have been on pin 8 (heater3) on the expansion plug was in the left most position (so actually on pin 6, E2_DIR), and while inserting it in said incorrect 2 & 6 pins, it seemed like the retaining spring part of the ground pin exposed on the side of the connector made contact to the 5v pin above it, but maybe it was the pin 6 that did it in, the bl touch is still working fine, but post popping the U3 chip (without noticing I was on pin 6 instead of pin 8 ) I plugged it in after realizing the USB powered it okay and the USB charger enacted it's internal protection at which point I changed it to pin 8.
long story short the 24V components all seem good, the U3 is definitely burnt, but I'm able to have everything work fine with the USB providing power. I am planning on using a hardwired 5Vin, likely using a deconstructed USB charger mainly for the built in OC protection.
Having looked at the schematics it does look like the 7.5A fuse is what feeds the 5V power supply, but am I correct in assuming that this would not have blown in the event of a 5V to GND short, even without double the recommended fuse size installed? I imagine that the 7.5A fuse is there in the event of an overcurrent event happening on the 24V side of the regulator?
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I guess I should also ask the question, should I take out any components if I'm planning on just leaving the U3 in there and using external 5V? I don't have access to a hot air station, but I do have a solder gun and could take out some of the larger components to isolate the chip in case there is a risk of a more catastrophic failure down the road...
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@Sir_Stig, not sure if you are monitoring this thread, but I'd love to hear if you had success. We're using a Duet 2 on our custom printer and yesterday we were working on installing a BLTouch, and we think we shorted our 5V. The result is as you described - total loss of 5V when powered from 24Vinput, but board powers when plugged in to USB. We've ordered a new "fuse" (the whole board
), but might try to revive the old. Wondering if your externally powered 5V did the trick? We are also thinking about trying some fine-pitch rework on the regulator, but that's a long shot for us old-geezers even with a microscope and fancy soldering station. -
@mikeabuilder You could provide 5v power via USB and run it like that.
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We did try just running off the USB, but the wifi interface didn't seem to work (maybe we blew that too) and also with the 7" PanelDu and DuEx connected, I think the laptop USB didn't have the current required. We had to unplug the PanelDu to get the board to power up (I hope we didn't blow that too). We might try a USB charger. The other thing that would be helpful would be any guidance from the HW debug team if they have experience with this dumb-a** move. Are there parts beyond that regulator that go when 5V is shorted to GND? Visually, our reg looks OK, and so do the nearby components. When we had our little event, we didn't get the oft-heard "pop", or "let out the magic smoke".
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@mikeabuilder You could share some close up shots of the board in case we can spot any other damage. Does anything else get hot when connected to VIN?
See here for options on providing 5v
https://duet3d.dozuki.com/Wiki/Power_Wiring#Section_5V_Options -
Here's a picture of the 5V regulator area of our clone Duet 2 (you can tell its a clone by the sloppy placement of several connectors). There is a slight blush on the part to the left of the U2 refdes (a FET, I think), but I think that's an artifact in the photo.
