The last time I had a chance to tinker with my malfunctioning PDP-8/A
with two RL02's was way back in Feb. 2013... here is the most relevant
tail of the old thread:
> The connections from the drive select outputs on the RL8A checked
> perfectly to the line receiver inputs on the RL logic board. While I
> appreciate Rick's taking the time to make me a selectable version of
> the RL02 oscillating seek.... he included a bug at no charge too ;)
>
> Specifically, the constant …
[View More]at 0230 (0100) selects the appropriate
> drive and resets it all right (0101 in AC). But - later on down the
> program, the SEEK (03) command is issued with another RLCB... however,
> the AC is forced to 0003 by the microprogrammed 7325.
>
> (As is probably apparent by now, the AC must have 0103 in it to select
> Drive 1).
>
> I edited the program to use a TAD 0231 and put the constant at 0231.
> So instead of the CLA CLL CML IAC RAL (load AC with 03 the hard way,
> an old-time DEC programmer's way to save one word when memory was a
> precious commodity) :) the AC now loads with 0103 and lo and behold,
> Drive 1 seeks merrily away! Restore the two constants to Drive 0 and
> THAT drive seeks. OK.
>
> However, all was not lost... during the couple of hours of chasing my
> tail wondering where the LSB of the drive select was going, I found
> that I had inserted the header into the RL logic board crookedly and
> bent two pins, one in the wrong hole and one shoved aside! :(
>
> Not only that, the line driver chip which provides the drive select
> signals had come from the factory with NO solder at all on its Vcc pin
> 16!
> =:^O
> Fixed that too.
>
> I think the OS/8 packs have been wiped out by now... various FAULT
> lights coming on, especially on the 2nd drive in the chain... going to
> build another system pack with VTserver which takes a good half-hour
> or more at 19200 baud. Hope the servo tracks are ok, otherwise I'll
> need to buy a couple of good packs!
OK. Last week I finally fired up the 8/A again. The problems had
actually gotten worse during the prolonged rest... I couldn't get
either drive to work this time (fault lights on both, as soon as the
Ready lights come on, even before any accesses). After much hair-
pulling and 'scope troubleshooting, I finally found (inside drive 1)
that I had improperly crimped one of the IDC connectors to the ribbon
cable, inside the bottom drive in the rack, where it was making a
variable resistance short between the two sector pulse drive lines!
So, having fixed that, I verified that Rick's oscillating seek program
works on either drive without faulting. Enter the constants for drive
0, drive 0 seeks no matter whether the first or second drive in the
chain as long as the unit 0 plug is inserted. Same for drive 1. Both
are not being selected simultaneously.
I also entered a short program to get the two status words, and that
reads the status of either drive correctly (idle, spin up, locked on
track 0, spin down, write protect button pushed).
Now, the original problem is still there, that OS/8 won't boot and the
RL02 faults (with either the original OS/8 pack that may have been
wiped, AND the remade one). Doesn't matter which drive is used as
Drive 0, or whether the new or the original OS/8 pack... Hit the BOOT
switch and Drive 0 audibly moves its heads, the fault light flashes
briefly, then it goes back to being ready (and of course OS/8 is not
running).
The interesting part is if both drives are loaded, then the fault
light on *both* drives flashes, then they both go ready again!
I haven't recently tried disconnecting the second drive cable and just
running with one drive, but that wasn't working before, either.
I am not going to be able to sort this out (unless I use my ancient
Tek 7D01 logic analyzer triggered by the fault signal) without a
diagnostic pack...
Does anyone have the diagnostic program set for PDP-8 and can put them
on an RL02 disc pack? I could either mail a disc to you, or I could
pay for one if a spare is available.
thanks for any help!
-Charles
[View Less]
Hi there!
Time to do some DEC collecting again...
Just wondering, does anyone have a MicroVAX II in BA23 pedestal chassis they'd be willing to sell?
Thanks in advance!!
-Ben
To Tom Gardner,
I'm working this week with Jason Honigberg. Did you know him at SyQuest? Is there anything specific I can ask him that might help you?
Billy Pettit
bpettitx at comcast.net
So, does anybody want to admit to winning the TU58-DA (desktop dual TU58 drive with controller) on eBay this afternoon? I sadly didn't win it, but I determined how much the winner had to pay for it. ;)
P.S.: I'm on the lookout for a TU58-CA, the rack-mountable version.
--
Mark J. Blair, NF6X <nf6x at nf6x.net>
http://www.nf6x.net/
Here's something you don't see on eBay:
Vintage PDP-12 computer was completely operational MUST PICK UP
http://www.ebay.com/itm/161199469414
Long Island, NY
How many of these exist? How much will this one go for?
-Glen
Folks,
I'm looking for a replacement SCSI to ESDI controller made by SMS for a Masscomp I,m trying to get running.
Its an SMS OMTI 7400 controller which supports ESDI/ST506 hard drives, QIC 02 cart tape, and floppy drive.
The current controller has failed in the floppy drive circuitry.
However I'm in the process of trying to source and replace the possible faulty components but I was wondering if anyone had a spare they would be willing to part with - for cash of cause.
Also looking for an …
[View More]ESDI hard drive, my Micropolis 1355 has failed but not the usual sticky bumper issue..
Many thanks
Andy
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I have a TK50 and M7546 (Q-bus) controller available.
The drive is pretty dirty, you will HAVE to open it up
and clean it before use, but it looks like it should
work after that. I don't have the cable, it was from
one of the boxes that had an interconnect board in
the middle between all the controllers and drives.
I'm in the St. Louis, MO area, and really only want to get
the packing and shipping covered.
Jon
> From: Pontus Pihlgren <pontus at Update.UU.SE>
> To: "General Discussion: On-Topic and Off-Topic Posts" <
> cctalk at classiccmp.org>
> Cc:
> Date: Tue, 21 Jan 2014 09:42:11 +0100
> Subject: Re: eBay PDP-12
> On Thu, Jan 16, 2014 at 02:51:54PM +0000, Adam Sampson wrote:
> > Pontus Pihlgren <pontus at Update.UU.SE> writes:
> >
> > >> How many of these exist?
> > > I can't know for sure, but here is a lower bound: 11
> &…
[View More]gt;
> > Robert Krten has a longer list of potentially-surviving PDP-12s:
> > http://dustyoldcomputers.com/pdp12/location.html
>
> All the ones I listed are in Krten's list.
>
> /P
>
The RICM is negotiating with a private collector to get a PDP-12 that is
not on Robert's list.
Michael Thompson
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Anyone here have a VAXBrick, or know what a fair price on one might be?
I've got a drop on one but the guy wants almost $2,000... I know they're rare and all, but that seems a bit on the ridiculous side to me...
I could be totally wrong though. Any input is appreciated.
-Ben
