I did the same repair on one of my Lexicons some years ago. It was also an bad ADC issue except the ADC was sending out random data that produced loud white noise when it came out of the DAC. I also got a chip from China... off eBay. Another issue common with these Lexicons as they age is the display gets very dim and you need to replace the capacitors on the back on the display unit.
Since the ADC is mounted on a dip socket from the factory, I suspect that Lexicon thought they may become a problem. The owner has reported back that the unit sounds better than it did before. I suspect that the ADC was on the way out for a while and just recently quit entirely.
