SKR Pro v1.2 Connected 5V endstop to signal, how much is dead?

So, I just built my MPCNC and it made it past pen plotting and doing a very simple cut (basic proof of concept) and I hadn’t finished routing wires and so I hadn’t hot-glued the wires into the SKR Pro v1.2 but figured I’d be ok (I was wrong).

Well, Z probe came unplugged and I figured I’d plug it back in, but had the 5v side backwards when I put it back in and now I’m fairly sure I fried things (it isn’t turning on).

Before I buy new parts. 1) is this repairable at all (or is it all damaged in the arm chip) 2) how much gets fried? just the board, drivers, screen?

Any help would be appreciated. Thanks.

I’ve seen Rambo boards survive this problem unscathed, so the first step is to completely unplug the touch plate from the board and see what happens. If it is still dead, check the fuses. I see three fuses on the pinout diagram. I’m not sure which one is for board power, so you will need to check all three. If the fuses check out, then the next likely culprit is the voltage regulator. I don’t have a SKR Pro board, but I think they have a jumper that selects power between the board and USB. If so, install the jumper and see if the board powers from USB. If it powers from USB and not from DC, then you will have a blown voltage regulator. They are fixable, but they are SMD components that can be hard to replace (at least for me).

So, I already unplugged everything but the screen. The 12v and 5v light are nice and bright, the 3.3v light looks barely lit. I checked the 3 fuses, and they all have continuity. I’m going to try the USB port (it crossed my mind as an easy way to see if the board survived but somehow fried the screen) for power, but I have to figure out where I tossed the cable :smiley:

I found the USB cable, and the 3.3v light flickers and and the screen turns on/off (at the same tempo).

If I could identify the part, I could bug one of my coworkers and see if he could replace it (I work at an engineering firm that builds boards like this, however I’m a SW engineer and my hardware skills are limited). However, I can’t see any burns and if it is only the board, it might just be another $60 on amazon to have one by the weekend…

Have pictures of the board?

So, messing around with the board, I accidentally discovered that it will boot up if I unplug the wifi unit I have. If the wifi is plugged in (which I hadn’t setup yet anyways), it causes the 3.3v light (top one) to be dim and if powered via USB, it causes the screen to flash on/off like I said before.

I don’t know what that means for my system though.

What an interesting result.

With the wifi module removed, is the board otherwise functional?

I just got back from the garage, and in marlin mode I can move XYZ and home Z (haven’t tried homing XY), so it appears to be functional for a cnc.

If I toss the wifi chip back in, it definitely stops working. So… don’t know what I fried, but at least I don’t have to buy another $60 board (yet, it could still have problems).

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I completely agree, PLUS, having the board repaired (if it can be) could end up costing you more than just replacing it. Your stepper drivers should be OK to transfer to a new board, or you can up your game with the latest mainboard from BTT for about the same price, plus new stepper drivers, although, your existing drivers will work with this new board.

Go to 3dprintingindustry dot com/news/bigtreetech-launches-two-new-3d-printer-motherboards-new-stepper-motor-drivers-209776/ to check it out.

It could very well be that your board is protected against or at least survived whatever your 5v miswire did, but perhaps the WiFi module is not as well protected against that, and toasted its own onboard power supply. Have pictures of the wifi module to share?

It doesn’t rule out that you overstressed something in your board and things could fail later… but if you’re lucky it may just be a toasted wifi module.

I can’t see anything wrong with either the SKR Pro or the wifi card. Its all of 4F degrees outside today, so my garage is fairly cold and limits how long I go out there, but all tests so far show the board is ok as long as the wifi card isn’t plugged in.

Do you have a DMM?
What resistance do you mesaure across Vcc and Ground?

I’ll bet you’re going to find that ESP-01 is toasted.
Good news is you can buy another one for $10…


It seems to vary, but ~900Ohm

When temp is under 0°C in my garage my skr pro board has heratic behavior, mainly she refuse to boot so at 4°F/-15°C yours might not like it at all.
Some electronical components have temperature tolerance and start to fail when temp raise the limits.

A simple test would be to warm your board few minutes with an hair dryer in mid power and see if your board is running better with the esp01 plugged in.

$10 is a bit pessimistic, I buy them in packs of five for $10… (

but you will have to flash it with ESP3D firmware yourself … even the BTT ESP01-s module from the official store will require flashing.

Chris’s basement has a good tutorial of what is involved

At that price I don’t think it is really worth messing about with them, if it is dragging the 3v3 down when you plug it in to the controller I would just bin it.

I agree that it’s possible to buy bulk ESP-01s from china, un-programmed for almost nothing. Buy a programmer, then spend the time programming them, and you can have them for cheap. I use them for other things- for example as serial console servers for embedded devices. Not everyone would consider it worth the time/effort to program them. Ryan sells them at a more than reasonable price in his store here considering that it takes time and effort to program, test, inventory, and ship. In fact, I think he under-charges for the value that is provided in context. Not to mention getting the capability to use the device for his customers in the first place- and then sharing the details openly. That’s high-value an high-integrity, in my opinion. Worth rewarding…

I probably wouldn’t bin the problem device, I’d dissect it to sort out why it failed. My guess is that the ESP01 has no protection for 5V overvoltage on the 3.3v supply. That in turn hints that the design of the host SKR pro 1.2 board is inadequately clamped/protected on that supply bus. A fuse and a zener at the header for the ESP-01, for example, would make it much less likely to blow up the attached WiFi peripheral. But then not everyone would find that investigation interesting or even possible.

This hints that there should be some more notes about potential pitfalls in handling enstop wiring. I know I’ve seen it discussed, but I bet this mistake happens fairly regularly.

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I’m well aware of cold limits on hardware. The hardware my company operates in extreme weather and yes, too cold can prevent booting or cause other weird issues. However, my issue occurred when it was warmer, and I was testing in my house (at 70F) before I took it back outside to connect to motors.

As for hints on the endstop page, I’m an SW engineer who works with hardware and I dabble in small electronics as a hobby (I can design simple circuits, but typically reference other designs to put more complicated things together). I was bit by the endstops not due to a lack of warning, knowledge, or experience, but impatience and thinking I remembered which pin was which even though I knew I should have double checked. This was all on me.

Thanks for the posts guys. I operate best when I’m just talking to people about my problems, so it helped me debug the board and get things working again. Now I just need to finish calibrating the endstops (currently running with none) and confirm everything is properly adjusted.

Did you follow a guide or how did you proceed with this?