The connections from the drive select outputs on the RL8A checked perfectly to the line receiver inputs on the RL logic board. While I appreciate Rick's taking the time to make me a selectable version of the RL02 oscillating seek.... he included a bug at no charge too ;) Specifically, the constant at 0230 (0100) selects the appropriate drive and resets it all right (0101 in AC). But - later on down the program, the SEEK (03) command is issued with another RLCB... however, the AC is forced to 0003 by the microprogrammed 7325. (As is probably apparent by now, the AC must have 0103 in it to select Drive 1). I edited the program to use a TAD 0231 and put the constant at 0231. So instead of the CLA CLL CML IAC RAL (load AC with 03 the hard way, an old-time DEC programmer's way to save one word when memory was a precious commodity) :) the AC now loads with 0103 and lo and behold, Drive 1 seeks merrily away! Restore the two constants to Drive 0 and THAT drive seeks. OK. However, all was not lost... during the couple of hours of chasing my tail wondering where the LSB of the drive select was going, I found that I had inserted the header into the RL logic board crookedly and bent two pins, one in the wrong hole and one shoved aside! :( Not only that, the line driver chip which provides the drive select signals had come from the factory with NO solder at all on its Vcc pin 16! =:^O Fixed that too. I think the OS/8 packs have been wiped out by now... various FAULT lights coming on, especially on the 2nd drive in the chain... going to build another system pack with VTserver which takes a good half-hour or more at 19200 baud. Hope the servo tracks are ok, otherwise I'll need to buy a couple of good packs! -Charles