Interesting RK8E fault

[Josh Dersch]

On Sat, Dec 8, 2018 at 7:24 PM Paul Anderson via cctalk <
cctalk at classiccmp.org> wrote:

> Are you using the same pack for the 8 and the 11
>

I connected the drive I normally use with my 11/40 to the 8/e for testing
to help narrow down where the fault was.
I used a 16-sector pack in all cases.

- Josh



>
> On Sat, Dec 8, 2018 at 8:54 AM Bill Degnan via cctalk <
> cctalk at classiccmp.org>
> wrote:
>
> > 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
> >
> > >
> >
>