Uno---Hot K170T511, USB in voltage drops form 5.0 Vdc to 3.8V and Pin 13 dies...

Hello,
Today, I was working a test protect for a 2D solar tracker with some 28BYJ-48 stepping motors for testing, that worked great. After finishing, and cleaning my breadboard, I tried to load a new program to my Arduinio UNO original, and noticed that pin 13 was not functioning… also the LED was always ON and dimmed… and flickering…
After closer inspection and testing Vcc it came down from the USB port from my macbook – 5Vdc to 3.8Vdc… and while checking the Vcc, I got burned by one IC… K170TS11… above 60 deg C
obviously there is an internal short…

any ideas on how to fix this problem? can the chip be changed? or the problem lies elsewhere?
Best regards

The chip is a common/cheap SMD LM358.
Half if the IC is a buffer between pin13 and the onboard pin13 LED.
The other half takes care of USB<>external power switchover by driving a switch fet (T1).
The IC itself could be faulty, or the switchover fet.
Replacing needs a temp controlled soldering iron and some SMD experience.
Leo…

Have you exposed anything on the Uno to high voltages? Like how did you drive the 28BYJ-48’s?

Thanks for the reply, it was very helpful.

The stepper motors 28BYJ-48 run on 5Vdc. My external power supply is 5.3Vdc. so I do not think any high voltages were generated. Always a common ground was shared between the Arduino and the External Power supply. I have done this setup many times… to test an idea it is nicer to use small stepper motors and write the necessary code. Once everything works as planned, then I ramp up to larger drivers for larger stepping motors… NEMA 23 or higher.

Now for the SMD LM358, I believe it was damaged. This board had only 1 month since purchased… I will try to replace it… or else RIP this board.

Thanks again.
Cheers

So you run the Arduino on the same 5volt supply as the motors. Bad idea.
Power the Arduino with a separate <=6.6volt volt supply on Vin, or >=7.3volt on the DC socket.

Short all four pins of one side of the IC with blob of solder.
Do the same for the opposite four pins.
Keep both blobs liquid solder untill you can slide the chip away.
Do NOT use force.
Then clean the board with solder wick.
The board might work ok without the IC.
You have lost the pin13 LED and USB switching, so try powering with USB OR external. Not both.
Leo…

Leo, thank you for your comments.

Actually, they run on two different supplies... one for Arduino and the second only for the motors. The motors supply voltage was set to 5Vdc however it can be varied up to 12Vdc. Both power supplies only share ground pin. As I have specified, I have done this for a long time.

From specs, I believe I could run the complete circuit with only one supply 7.5Vdc 15A, connected to Vin. and as soon as the circuit senses the higher voltage, it will disconnect the USB power supply; allowing only for communication. However, I always try to separate both circuits.

I will try to remove the IC from the board as you recommend. and see what happens.

Thank you for your help. it is great.