Giving this thread a bump...

Posted an ad for a Timewave DSP-599 a few weeks back. Was contacted by a guy handling an estate and was offered one for $110 plus shipping.

Oh...what the heck. I've been missing out on all of those $275+ ads by mere minutes !

Got the unit in the mail earlier in the week; tested it last night. Everything but the "Low Pass Filter" adjustment worked properly. Dived in and found that the chopper disc of the leftmost opto-encoder assembly had somehow come loose and wouldn't turn with the knob. Had to desolder the daughterboard which holds the mode-set pushbutton (it fits over the encoder assembly) then a dab of epoxy secured the disc. Let it set overnight then trued the disc up...resoldered the board...reassembled and tested.

Voila! Full functionality!

This '599's Rev4.0 firmware also has the now-discontinued CTCSS Decode test function, and a spare PROM shipped with the unit might be Rev5.0 firmware - the seller indicated that it had been (or was in the process of being) upgraded.