On Fri, Dec 7, 2018 at 9:58 PM Josh Dersch <dersc...@gmail.com> wrote:
> Hi all -- > > Finally got all the parts together (and my act together) to actually get > an RK05 lashed up to my PDP-8/e -- only took a decade or so :). I fixed a > few problems with the RK05 and it appears to be behaving very nicely. > > The RK8E controller is mostly working properly but fails interestingly > when running the formatter, and during the exerciser -- on cylinder 128 and > 192 and very infrequently on cylinder 64 it will get a cylinder mismatch > when doing the seek. When running the formatter during the verification > pass, on cyls 64 and 128 if I retry the read it'll continue without issues, > but it's never successful on a retry on cylinder 192. I tried hooking it > to the RK05 in my 11/40 and it exhibits the same behavior, so I'm guessing > the drive isn't at fault. And the error is consistent across packs (of > which I have only two). > > Apart from that fault the drive and controller seem to work fine -- I > wrote out an OS/8 pack with Adventure on it (or at least the first 191 > cylinders of it) and it works without issue. > > Reading the RK8E service docs and schematics, the cylinder address compare > is done by reusing the CRC buffer, so I suspect the issue is in or around > there -- the big problem is that debugging it is rather painful since that > logic is in the middle board of a three board set, with jumper blocks on > top -- so bringing it out on an extender isn't an option. I'm curious if > anyone's seen this issue or is so very familiar with the logic that the > fault is obvious. > > I suspected the 7496 shift register at E14 which takes in the cylinder > address to be compared w/the header on disk, and I went ahead and replaced > it in the hopes that I'd get lucky, but no go. > > Anyone have any advice? > > Thanks, > Josh > > I'll add that during the format/verification the drive seeks properly (i.e. it's not missing a step or overstepping), which I've confirmed by watching the thing walk through the tracks with the cover off. - Josh
