the AIC26 doesn't work properly!

After having solved the problem of not  working , the aic26 worked  normally later. But   good times don't last long , 10 or more days later , with no any condition  changed, the aic26 DOUT pin couldn't send signal anymore. then I made another one pcb. similarly, after having  worked normally some days , the DOUT pin didn't send signal either. but what is the reason?  thanks a lot!