Problem with making an Arduino-like board

Question

I'm making my own Arduino-like board with an ATmega328p and an FT232RL. After realizing the circuit (making sure everything was correct) I had some prototypes made by JLCPCB. Later I bought the various components on eBay, among them the AtMega328p-PU with bootloader which I hope has the bootloader already loaded. I then proceeded to solder the various components. It was my first time soldering SMD components, using a hot air gun set at 400° Celsius. For soldering, I used the solder paste xg-z40 from mechanic.

After soldering it, I noticed that the USB connector had not adhered properly (especially the pins, as it was partially raised), so I had to reheat the component to make it stick to the board.

Once this process was complete, I connected the board to the computer, but it gives me no signs of life. Unfortunately I have not included the 'ON' LED on the board, to verify the correct switching on of the board, but in fact the computer does not recognize it. I tried to install the drivers (for the serial interface I put the FTDI FT232RLSSOP chip), but nothing. The board, when connected, does not heat up at all. I would not like to have fried the components due to the high temperature during soldering, or that the pins of the USB connector are not soldered well.

I was wondering if it could also be a short circuit problem, always caused by soldering.

I am currently at a standstill and don't know what exactly the problem is. I await some advice, thanks.

Schematic: Schematic

PCB preview: Preview

• TonyM: A very warm welcome to the site. Unfortunately, this is a very broad question, impossibly so without providing a schematic. To start with, please can you edit your question to add the schematic, preferably embedded in it unless impractical, rather than by link as links can break over time. And good, sharp, photos of your work, cropped so we don't have a scrollfest trying to read it :-) Thanks and again, welcome.
• Transistor: ... and good sharp, cropped photos of your work.
• Chris Stratton: Your schematic shows an FT232RL so this cannot be an "uno" as it lacks the 2nd ATmega for USB which is the most key characteristic of one. Please correct your description of the board. Check power supplies and realize that the FT232 should be recognized by the computer even with the ATmega328p removed or unprogrammed.
• Chris Stratton: Given this is not the design of the Arduino "UNO" you claimed it to be, where did you get the schematic? Did you make any changes? It's probably an assembly problem or very slightly a bad parts one (eBay...) but design errors need to be ruled out too.
• smajli: Are you sure that 5V is not connected to 3.3V? When you look at schematic, left-bottom: the VCC close to the switch is one of 5V(from regulator or USB) and then right-bottom there is 3.3V going to NRF24 and VCC. I know it may be intentional, but be careful with labels, there is a chance the software create a link between 3.3V and 5V lines frying most of 3.3V powered chips. Using continuity meter check there is no link (or ensure your 3.3V chips are 5V tolerant),

Answer 1

First, clean the board thoroughly with an appropriate solvent such as 99% isopropanol or a petroleum based solvent, removing all flux and look at it under a microscope or magnifier. Fix anything that looks dodgy. Use at least 5x magnification, enough that you can see the solder balls in the paste if they are not melted. Tilt the board to and fro to catch anything not visible from directly above.

Since you've already powered it up, try that again and check that power supply voltages exist everywhere they should. I suggest using the USB power source. Be extremely careful not to short the probe when checking lest you add to the woes.

At this point your FT232 should show up as a COM port on a PC if you have the correct driver installed. Get that working first, only a few parts are associated with the USB-to-serial converter. If there is a hardware problem it's likely to be associated with the power or the two USB signal wires.

• Gianluca Grasso: I currently do not have isopropyl alcohol, nor a tester. I tried to change the USB cable (the one used previously, is a USB cable bought on AliExpress for Arduino Nano), connecting one I found (not an Arduino cable). As soon as I connect the USB cable, the fuse heats up a lot. If, on the other hand, I connect the cable bought on AliExpress, this does not happen.
• Spehro 'speff' Pefhany: You should have both of those (and more) if you are going to be assembling PCBs.
• Gianluca Grasso: Yes I know. Gradually I buy everything I need.
• Gianluca Grasso: Regarding the behavior of the fuse, any advice?
• Spehro 'speff' Pefhany: The difference between the cables is disturbing, but without a multimeter I hesitate to make a guess. If you have a known-good cable, try that.