It's been a while since I started into the -515, so here's a blow-by-blow on what was found.

First, the radio appeared deaf on several bands (verified with a signal generator). The other apparent issue was the failure of the accessory CW filter (or was it? More on this later.) A dialog with Walt, PE1ABR regarding the working of IC61 (a uPB249 ROM on the Synthesizer Board) and its action on IC1 (an SN7445 8-line decoder on the RF Board which controls RF bandpass filter selection) motivated me to test IC1. Several of the decode lines appeared active (low) at once, while others never went low. Removal and replacement was in order.