Daniel asked: >The problem is that from the 1000 boards I test, about 25 aren't >running at all. Replacing the xtal usually solves this problem. >Sometimes the board works well in the pretesting phase, but fails >at the final test. Current xtal brand is TXC, but we've had similar >problems with other brands too. What crystal package are you using? With some packages it is possible for PCB manufacturing process residue to get trapped under the crystal. When you unsolder the old one, it boils off any trapped moisture and the replacement crystal works fine. Of course, the more margin your oscillator circuit has, the less likely this is to make a difference. Clues: modest application of dry heat from heat gun causes failed oscillator to start. Application of condensing moisture by directing breath through a straw at crystal footprint causes oscillator to stop. Reg Neale