So I changed the BR1225 batteries in my 3500 and 3400. After reviewing advice in the forum, I then reset the clock, re-enabled various pages on the page list, and also reviewed the knob list.

Unfortunately the ALT and MIN-ALT bug options are grayed out and can't be selected for use in the knob list. The 3500 still works with the autopilot (a TruTrak Vizion) fine in lateral mode (both LAT-HDG and LAT-NAV work, including when using GPS) but the unit is no longer capable of bugging an altitude or setting a minimum altitude as before. Also if you try to set VER ARM it just gives up after a few seconds. The ends of the flight director bars remain gray at all times.

Any ideas on how to fix this? Thanks!