RK05

Hi, I'm trying to repair my RK05 drive. It seems that it doesn't find track 0 when loading the heads, thus moving the heads to the inner limit, forcing a return-to-zero and starting all over again. I think the fault is on the M7681 card (cylinder address and difference), the output of E16 pin 8 (CAD3 zero detect H) doesn't change, nor does the input on pin 10. And here comes the problem: the M7681 isn't described in any DEC documentation I've found so far (apart from the schematics), only the older M7702 card (the function is practically the same, but they are completely different designs). The new card contains several undocumented TTL ROMs (8223). The output of pin 6 of E1 goes to the input pin 10 of E16, probably a difference==zero bit. So here comes my question: does anyone have a ROM listing of these ROMs, especially of E1? I'd like to know what exactly that ROM is doing. Christian