Interesting RK8E fault

[Bill Degnan]

On Sat, Dec 8, 2018, 1:02 AM Josh Dersch via cctalk <cctalk at classiccmp.org
wrote:

> On Fri, Dec 7, 2018 at 9:58 PM Josh Dersch <derschjo at 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
>

Partitions as rka0 / rka1?
B

>