On Sat, Nov 3, 2018 at 1:12 AM Lyle Bickley via cctalk <[email protected]> wrote: > On Sat, 03 Nov 2018 15:13:16 +1100 > Guy Dunphy via cctalk <[email protected]> wrote: > > > This is rather sad. > > I've received a PDP-8/S. It turns out to be missing so much, that > > it's probably beyond restoration. Anyone who can think of potential > > ways to find the missing parts, please speak up. > > > > http://everist.org/pics/PDP-8S/ > > > > Missing: > > > > - Front panel PCB, > > - Case top AND bottom, > > - Power supply. > > - Some flip-chip slots are empty. Not sure if supposed to be. > > I have a restored and running PDP-8/S. > > It looks to me that you're not missing modules - the open slots are > for the I/O cables.
Yes. Start by looking at http://www.ricomputermuseum.org/Home/equipment/pdp-8s At a quick glance, I see you _might_ have 2-3 cards in wrong slots near some intentional gaps. Check that. The open slots at the back are for the I/O cables. The open slots near the memory stack are supposed to be empty with the one possible exception where I see in your photo you have a single-height amber card and the RICM PDP-8/S appears to have a dual-height amber card. I don't have the printset up so I can't tell exactly what's going on there. Could be normal variation as they made changes across the run. > The P/S is a standard DEC linear P/S and can be easily substituted until > you come across the real thing. Yes. You just need enough amps at +10V and -15V to fire it up. What I don't know off the top of my head is the difference between a table-top and rack-mounted system. RICM has pictures of a rack-mounted system. Mine is table-top. It's entirely possible that yours was pulled from a rack and the PSU stayed behind. Yours might never have had covers like the desktop unit. > You need to get the schematics for the version of the PDP-8/S you have > and check the modules in your system against the module chart. Yes. "for the version you have" is important. I don't think there's exactly one way they built it across multiple years. There can easily be a module or two different between different manufacturing dates if there was a large ECO. > When you say the front panel PCB is missing - do you mean that there > is not a large circuit board with incandescent lamps in the system? > That would seem unusual to me - given that all the switches are on the > front panel. Unlike every other machine I've worked on, the -8/S has *two* front panel boards. One is very short and has just the switches and sits in slot 1. The other is full-sized and has only the lamps, no switches and sits in slot 2. I see from your photos, that board is missing. Given that it's fairly simple, you might be able to find a Unibus hex-height protoboard and fabricate a replacement. The lamps might be interesting to source - ISTR they have 28V filaments, underdriven to give them a long lifetime. I can't recommend the original lamps anyway - they are not the bi-pin bulbs used in later models (PDP-8/L and newer). They have these brittle leads coming out of the glass and no plastic base. I have several in mine that had the leads break off right at the glass. Even if the filaments are intact, these bulbs are essentially dead. I do not presently have any replacement bulbs of any type for mine. > > Also there's no sign of any I/O circuitry. > > There is NO I/O on a PDP-8/S. The I/O cables connected to any I/O that > existed. Yep. All the I/O was external on the Negibus, even the console TTY (there's a PT08 in the base of an ASR-33 that was standard for this model). I didn't get the TTY with mine (it was long gone, to a Ham club, I was told) so I don't have a console SLU either. Once I get the CPU working, I'll have to fabricate a PT08 replacement. There just wasn't room in the box for any I/O. The backplane on this model is close to half the size of the backplane on a Straight-8. > Please get a PDP-8/S service manual and schematics... Definitely. -ethan
