>> -----Original Message----- >> From: ard(a)p850ug1.demon.co.uk [mailto:ard@p850ug1.demon.co.uk] >> Sent: Tuesday, August 03, 1999 1:43 PM >> To: Discussion re-collecting of classic computers >> Subject: Re: RX02 Repair >> >> >> > >> > I've been trying to bring my old RX02 drive back to life, >> with little >> > success. >> > >> > I just received a good bootable floppy, and get the same >> results as with all >> > my old disks, so now I'm looking for hardware problems. >> > >> > On a PDP-11/03, With RXV21 controller, and an RX02 drive, >> the RX02 >> > initializes, attempts to read the boot block, and crashes >> to ODT at 000600. >> >> I am going to assume that this is a double-density disk >> (and thus has 256 >> byte sectors) and that the DIP switch inside hasn't been >> moved since it >> last worked on an RXV21 (I can't find the info quickly, or >> I'd tell you >> how to set it). >> >> > >> > >> > > In examining what my system reads as it attempts to >> boot, it looks like I >> > > read every other 128 byte chunk correctly. I haven't >> figured out a >> > pattern >> > > to the corrupt sections. >> > >> > >> > Does anyone have any RX02 diagnostics, or hardware >> trouble shooting tips? >> >> >> Argh!. Fixing an RX02 is a lot worse than fixing an RX01 (I've done >> both). The RX01 has an internal diagnostic connector that >> you plug an >> KM11 into. You can then single-step the microcode, >> halt-on-error, etc. >> >> Anyway, back to the RX02. The controller is the upper board >> in the drive >> unit. Undo the screws and hinge it up. On it there's a microcoded >> processor based on 3 2909 sequencers and 2 2901 ALUs, 1K of >> ROM and a lot >> of TTL glue. There's also a 2K bit sector buffer based on 2 >> off 2102 RAMs. >> I can talk you through it if you can get the printset. >> >> >From the fault, I suspect that most of it is working >> correctly (most of >> the logic is the same for all bits in the sector), and that >> the most >> likely problem area is the sector buffer and/or its address counter. >> >> There are some things you can try. Firstly (if you have the >> programming >> info - if not I'll find it), you can try transfering 256 >> bytes from the >> PDP11 to the sector buffer and then transfering it back >> again (without >> going via the disk). This will test most of the controller >> logic and the >> sector buffer RAM. My guess is that this will fail. >> >> Now look at the siganls to E56 (a 2102 RAM that's the high >> half of the >> sector buffer). Does it ever get enabled (pin 13 goes low)? >> Check back to >> E29f (74LS04) if not. If that inverter is OK, then suspect >> the address >> counter (E63, E57, E51). >> >> Also suspect E56 itself (this is the most likely problem, >> actually). If >> you have a spare 2102-1, it may be worth replacing it. >> >> >> > >> > >> > Steve >> > >> > >> > >> >> -tony >>