In the thermal printer and printer mechanism world , there is another matching components called control board or PCB. Today we are going to share some common happen PCB board hardware mistakes happen in pos printer board , label printer board .etc .

Lesson Learned (HW/PCB/PCBA) 

Let's talk about failures and mistakes...
I prepared my own _subjective_ list of popular HW mistakes.
I committed many of them myself (1, 2, 3, 6, 7), and I encountered many while hardware debugging.

So this is the list:

1. "RX/TX" issue - swapped complementary function lines, e.g. RXD/RXD, SDA/SCL or MOSI/MISO mismatch, plus and minus mismatch in diff. pairs (e.g. USB, RS485).

2. Wrong footprint assignment, e.g. used SOIC NARROW instead of SOIC WIDE, TSSOP instead of TQFP.

3. Wrong footprint pitch - e.g. used 0.5mm pitch instead of 0.55mm.

4. "Mirror" mistake - rotated or mirrored schematic symbol.

5. Unconnected ("floating") lines - e.g. unconnected CMOS input lines, unconnected important lines.

6. Wrong pin assignment - e.g. interfaces connected to improper MCU lines, output signals connected to the input lines.

7. Wrong logic level - e.g. EN line connected to GND, nRST activated by a high level.

8. Improper component placement - bypass capacitors far away from power supply lines.

9. Shorted lines - e.g. by mistake CAD tool can short component pins.

10. Reversed component polarity - e.g. swapped +/- pins on polarized capacitors or LEDs.

Do you know another interesting, often happen bugs?