we have a system with ADSP-2191M that starts in bypass mode (BYPASS pin unconnected). After successful start the program sets PLLCNTL to required multiplication factor (CLKIN=40MHz, multiplier=4x to achieve 160MHz CCLK) and switches CCLK to be driven from PLL, ie. deactivates bypass mode. From this time the processor stops executing its program. Processor reset does not help in this case, ie. after another reset the program running fine while in bypass mode but stops as soon as bypass deactivated again. Power down and up the board will sometimes help (ie. the program is running fine even after bypass mode deactivated), sometimes does not. We have hundreds of boards running fine but the last series suffers from this problem. Do you have some hint what we can check, please, that could cause PLL is unusable?