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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.

enter image description here.

I upload photos of the pcb. Second design on the right (Image B) recognized.

enter image description here

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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.

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  • \$\begingroup\$ I assume that fixed it, otherwise there are known USB/Port driver version and Chip date code incompatibilities. \$\endgroup\$ – Sunnyskyguy EE75 Jun 10 '17 at 19:39
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I soldered only two PCBs, one from each design. As filo mentioned the problem was on TEST pin. The second PCB (image on the right, B) worked because both PCBs were soldered by hand and TEST pin (pin 26) short circuited with AGND (pin 25) coincidentally during soldering process.

I connected TEST pin to GND and worked.

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