I designed two boards that contain an FT232RL FTDI chip.
The difference between two boards is only in the USB data lines.
One of the two PCB designs (Image A) does not recognize the FTDI chip. I noticed that when I unplug and again plug in the USB cable very quickly the FTDI chip gets recognized. However, if I do not do this quickly enough, the problem still remains.
The schematic is identical for both PCBs.
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I upload photos of the pcb. Second design on the right (Image B) recognized.
Best Answer
Your TEST pin is floating. FTDI datasheet says "Puts the device into IC test mode. Must be tied to GND for normal operation, otherwise the device will appear to fail."
How many PCBs each have you tested? If only one, then manufacturing differences between chips may make the difference.