Testing is important to deliver a quality product. I just finished another batch of XTB-523's. I check the transmitter waveform and peak-to-peak output voltage. Then I check the input sensitivity and verify the bandpass amplifier is centered at 120KHz. Then injecting 120KHz noise just below saturating the amplifier, I verify it will still decode stronger X10 commands. After that I install the cover and plug it in one last time to make sure the LED had slipped into the lens.
The LED didn't light on one of them, so I assumed it had not gone into the lens. I took it apart and made sure it went into the lens when I reinstalled the cover. Still dead. Hmmm...
I took the cover off and it worked fine. Back on, dead again. After verifying all solder joints were fine, I discovered the LED dimmed and went out when there was any pressure on the transformer bobbin. The cover just touches the bobbin, which was causing it to open circuit. It works fine after the transformer was replaced.
With thousands shipped, that's the first one to behave like that. If I didn't bother to re-check the LED after the cover is installed, it would have been dead when the customer who received it plugged it in.
Testing is important...
Jeff