I can't engage AUTO with the front panel keys (with the YS1700 ro YS1500).

Please check the following 2 points.

1. Is the hard manual switch ON?
2. Is the C/A/M mode key lock on LOCK?

Note: To avoid changing modes unintentionally, the instrument is designed so that you have to hold down the C/A/M key for approximately 1 second or longer to switch modes.