# Diagnose USB port damage

A week ago I made a circuit based on a PIC16F877a uC and MAX232 ic for RS232 serial communication between PC and device. I used USB port of my laptop to power the circuit as:

Image source: bharatbalar.wordpress.com


The circuit ran fine but after almost five minutes the MAX232 ic become very hot, I immediately disconnected the circuit from my laptop. Now the problem is that my usb port is not working although it is giving power to other devices, the area where usb port is located always remains hot even when the system is turned off and the battery of laptop completely drains in off state. I tried shorting the Positive and ground pin of USB port but instead of turning off the system a message appeaser on screen showing that the device connected to USB port is exceeding the power limit of its HUB. I visually inspected the motherboard but did not find any damaged/burned component. There are two USB port and both are not working.

What solution do you suggest for this problem?

• Your diagram does not show how you connected the circuit to your USB. MAX232 and F877 chips are generally quite robust, except for excessive things like reverse power or serious overvoltage on the power. Your test of shorting the USB power is not something I would recommend: the USB hardware is required to keep the short circuit current within safe limits, but not all PCs implement that faithfully. If you want my honest opinion: your USB ports are likely to be damaged beyond repair. – Wouter van Ooijen Oct 13 '13 at 19:49