Help with UC300ETH-5LPT, burnt chip?

[n879]

I recently bought a UC300ETH-5LPT so I can use ethernet and UCCNC on my Romaxx router. I hooked up the UC300ETH-5LPT to my laptop last night via ethernet and got it updated and communicating ok. I used a 5V/0.7A usb charger and it seemed to work fine.

Today I plugged the IDC26 cable into the BoB and port 2 of the 5LPT and the UC300 wouldn't power up with the usb changer. I checked the voltage on the terminals and it was reading less than 1V. At the time I figured the usb charger wasn't powerful enough and hooked up my other RD-35B 5/24V PS. As soon as I powered it up with the RD-35B I got a puff of smoke out of the 5LPT. I powered it off asap. Yes I used 5v not 24v. See image below for the burnt chip (npn/pnp transistor?).

Big

To see if anything still worked I unhooked the IDC26 cable and used the usb power supply and the UC300 still worked ok. I then removed the UC300 and plugged the RD-35B into the 5LPT and it still seemed ok. I think I did see a couple small puffs of smoke when checking voltages on the port pins, but nothing like before. Most of the pin 26s are reading ~4.6V now (should be 5V I think).

There are a bunch of pictures of the machine and BoB in the album.

Does anyone have any ideas what happened? How should I proceed?

Any help would be greatly appreciated.

[cncdrive]

If the circuit burnt then it likely got an overvoltage. Over about 6Volts.
It is possible that the PSU could not supply enough current and when the board was unpowered then the voltage quickly rised because the PSU could not compensate due to the overcurrent and for a second that could possibly cause overvoltage and damage.

Your picture does not show up for some reason, so I don't see what seems to be burnt, but if the circuit got overvoltage on the power input then it is likely that too many things damaged for a repair.
Ofcourse we can check the board to see if we can repair it or better to say if it worth repairing it, because if for example all ICs damaged then the repair time and cost would be more than a new board.
It is also possible that something got shorted out, e.g. an output and that died in short circuit and then the repair is relatively simple.
But I really can't tell you without seeing and being able to take measurements on the board.

[n879]

Can you see this image? https://photos.app.goo.gl/NUCGUc6dmSVrLrCU8
The chip closest to the edge is the one that smoked.

Vmax549, I will check pin 26 of the BoB for voltage.

[cncdrive]

It is an SI2315 P-channel mosfet.
It's purpose is to protect against reverse polarity on the power input.
That it burnt indicates that there was a heavy overcurrent, more than about 3Amps current flew through the mosfet.
It can be a short circuit on the board which could cause this or something is shorted out externally, e.g. the 26.pin (5Volts output) in the IDC connector is shorted to ground.

[n879]

OK. I checked pin 26 to ground and to pins 25/24 on the BoB and did not measure any voltage.

Then I checked resistance from pins 26 to 25 and 24, etc and got ~ 0 ohms. So I'm assuming that pin 26 is set to ground on the BoB.

[cncdrive]

Yes, if the 26. pin to 25. pin is 0 Ohms then there is a direct connection between the 2 pins which means that the power supply is shorted out through the Mosfet transistor on the board.
The Mosfet can't withstand that condition too long and so it burnt out.

[cncdrive]

You could remove the mosfet from the board and connect the source and drain together to bypass it and then the board will work again,
but then you risk that if there will be still a short circuit then the traces on the board might damage, because then there will be no mosfet to burn and protect the board from the heavy overcurrent.
So, it's much better to replace the mosfet with a new one.

[n879]

What are the chances something else on the board(s) are damaged? Is it worth trying to replace the mosfet? If so, would one of these work?
https://www.digikey.com/products/en?keywords=SI2315%20

Once I replace the mosfet or get a new 5LPT board what would be the best way to deal with this? Should I just cut & terminate wire #26 on the cable so the BoB never sees the 5V from 5LPT?

[cncdrive]

I can't tell you chances (%). If it was only overcurrent/short circuit then it is very likely that only the mosfet damaged and nothing else.
If it was overvoltage via the power input then it is very likely that more things damaged.

The Mosfet you linked is the one what is on the board.
If you thinking between getting a new -5LPT or replacing the mosfet then it worth to replace the mosfet first, because you can't loose much. In worst case the board will not work.
If the 5V (26. pin) is connected together with the ground 18. to 25. pins then you will have to separate them and for that one solution is to cut the 26. wire or to make a cable which only has the first 25 wires and missing the 26.

[n879]

Ok. I ordered the mosfet and will try and replace it. Thank you so much for your help.