Today I came across a small problem – my brand new USB-UART dongle wasn’t working. It connected to the PC correctly, drivers were installed etc, but the UART side just didn’t work. I have bought a few of these from eBay previously, and usually they work right away, but this time it wasn’t the case.
So I observed the problem: my board started taking more and more current as I sent packets over UART. Than I looked over the board under a microscope, and resoldered the pins. No effect. Than I decided to take the chip off, and see what was under it and there I found the problem. Image below.
The board is based on CP2102 chip, which is in a QFN package, that has a ground pad underneath. And in case you are wondering, these two lines under there are RX and TX, shorted out by the ground pad of course. Chinese engineering at is best. So since I needed the thing to work and decided to fix it. So I took a piece of kapton tape and put it under the chip and resoldered the chip on top of it.
And yes, it worked.