> From: Jerry Weiss
> I am trying to understand how the diagnostics didn't reveal this defect.
Vondada #12: "Diagnostics are highly efficient in finding solved problems." :-)
Noel
[oops, accidentally replied directly instead of to the list]
On 2/13/19 12:54 PM, Ethan Dicks wrote:
> It's interesting that it was a bad 7430 in [your RK11-C]. I find that for equipment of that vintage, my usual suspects are failed 7474s and failed 7440s, probably 80% of the total. Behind that, it goes 7420s and then maybe 7430s.
Looking back over my repair log, my totals just within the RK11-C were:
2x 7430 (M119, M795)
1x 7420 (M141)
1x 7401 (M149)
1x 7400 (M203)
> > > Likely some disk controllers did NOT SUPPORT crossing 64K boundaries!
> >
> > No; the RK11 spec says "[the two extended memory bits] make up a two-bit
> > counter that increments each time the RKBA overflows".
> >
> > The actual error turns out to be slightly different to my guess; there's
> > a spurious overflow from the low 16-bit register to these bits at 0170000.
>
> Maybe a problem with E29 or E34 on the M795 module?
I am finding this entire discussion extremely fascinating!
Every day I look forward to reading the latest twists in the
plot. The ideas, hunches, tests, dead ends, and results are an
excellent example of the debugging process.
I am awaiting the exciting Perry Mason style conclusion, where
the guilty chip stands up and confesses on the stand. :-)
Alan "Where were you on the night of the crime?" Frisbie
> From: Alan Frisbie
> I am finding this entire discussion extremely fascinating! Every day I
> look forward to reading the latest twists in the plot.
I forgot to mention the most amazing part of the whole story: he first
acquired the machine while he was a student (I think?) at CMU, decades ago,
and has been dragging it around the country with him ever since!
He's also had to do a tremendous amount of work on it to get it running,
starting with building an entire new power harness. He's also had to find and
fix a long list of failures, all over the machine; there were bad chips on
almost every board in it.
Fritz has written most of the whole adventure up:
http://fritzm.github.io/category/pdp-11.html
it's an incredible story.
Noel
> From: Alan Frisbie
> I am finding this entire discussion extremely fascinating! Every day I
> look forward to reading the latest twists in the plot.
:-)
> The ideas, hunches, tests, dead ends, and results are an excellent
> example of the debugging process.
Yeah, and it was a Duesie of a problem, too.
Although once we got clear of the bad data from the console and my confusion
about R5, and it became clear that in the Unix failure, the pure text was
being damaged, from that point it was pretty straightforward to track it down
(albeit one that needed detailed understanding of how V6 handled pure texts -
and luckily I'd come to understand that part of the system a bit while getting
the QSIC running).
Fritz's lucky discovery, early on, that it was location dependent was also a
big help.
Noel
Hi,
I'm (still) trying to reverse-engineer a ton of M68K ROM code which was
apparently compiled with a circa-1990 C compiler.
Does anyone have copies of any of the following -- or any other C
compilers for the 68K which were around at that time?
* Sierra Systems 68000 C compiler (was part of some Sega Genesis
developer kits)
* HP 68000 C compiler (either the HP 64000 or MSDOS versions)
(I believe this was sold as the "HP B3640 Motorola 68000 Family C
Cross Compiler)
* Lattice C
* Anything not on this list ;)
My game plan is to take the compiled standard libraries from these
compilers and build up some patterns/"fingerprints" to try and make a
better guess at what the code is up to.
I figure if I can at least pin down the stdlib and floating-point code, I
have a better chance at figuring out what the main code does.
I've seen the HP cross compiler manual on Bitsavers, but the compiler
itself doesn't seem to be on bitsavers/bits.
Thanks.
--
Phil.
philpem at philpem.me.uk
http://www.philpem.me.uk/
Does anyone here still actively wire wrap circuits? I am thinking
about dumping my inventory of nice machine pin wirewrap sockets.
Lately they have been selling like lead balloons.
Contact me off list.
--
Will, in the Hudson Valley
jnc at mercury.lcs.mit.edu (Noel Chiappa) wrote:
> > From: Alan Frisbie
>
> > Harbor Freight sells a nice hydraulic lift table for under $200 that I
> > have found very useful for that sort of thing. It doesn't go up very high
> > (like for the top of a rack), but I used it with some wood blocks
>
> Thanks for the tip! I got one on sale for about US$140; it's _very_ sturdy.
> And the top is just large enough to hold two milk crates (available at
> Home Depot, BTW), so it's guite easy to build up a stack as high as one
> needs to reach the top of a 6' rack.
Thank you very much for the feedback -- it makes me happy when I
know that someone finds my suggestions useful.
I've used the milk crate technique myself, with a piece of sheet
metal on top to make it easier to slide the load off. I hope you
secure such a stack tightly. :-) I used some of the inexpensive
1" wide Harbor Freight cargo straps.
Alan "You can't have too many clamps or straps" Frisbie
https://www.ebay.com/itm/132933407806
this is interesting because of the price and that all of the Sun drives
I've ever come across had the 800bpi option in them
