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A new PDP-8 in the collection!

A

anders_bzn

Experienced Member
Joined
Jan 27, 2016
Messages
264
Location
Sweden
This summer I finally got a PDP-8/E into my collection. I swapped some computers with a friend, I got this and he got some others... This machine must have been the cheapest PDP-8/E that you could buy. It really don’t know if the configuration makes sense, could one even av any use of a DECTape drive without OS/8 and 8(or 12)K of RAM.

It came with:
  • Only one backplane
  • 4K of memory
  • A TU56H (and TD8E)
  • PC04R (reader only)
  • KL8E wired for 110 baud current loop

I have some cards in my collection that should go into this machine.
  • The RK8E along with the RK05, this have I restored and used with my PDP-8A but this has been put aside for a while since I lack space.
  • A extra KL8E, for serialdisk maybe.
  • A RX8E, and a RK01 (I think I have one extra from my PDP-11’s)
  • An extended memory control board M837

I would like to get my hands on
  • 8K memory stack, one or two :)
  • A second backplane. I have one on loan but I’m missing the power cable harness.
  • The bootstrap module M847/MI8E in some version.
  • For a start I can use two 4K mos memories that I also have lying around.

So far I have replaced one broken fan in the PSU and tested it (without load so far) I have also replaced all broken light bulbs on the front panel (this drained my stock completely) and tested it in my PDP-8a. It has issues with LA. The machine seams to be in good condition, only minor issues. One toggle switch for example, but not in the usual way.,,
IMG_2674.JPG IMG_2675.JPGIMG_2738.JPG
 
Is the label on the back still there and readable. The label I am talking about has the slot numbers and option and board type. Would tell you what was originally present and where.

Until about a year ago I had not heard of the PC04R, I thought all of them had both reader and punch. Your reference confirms that was a option.

It would have been interesting to know what this machine was used for. The TD8E needs quite a lot of code to make it work so I could see only some custom application but I can't imagine what it would be with the hardware it came with. Probably there are boards that were removed.

Another fun project!
 
I know that the CPU timing board M833 has been swapped with a M8330 by the previous owner. But it has never been running with this board. From the label it seams like the M865 has been replaced at some time. The TD8E is not noted on the label so it has never been used in this machine (I suppose, which make sense). I think that the previous ower both the TU56 together with the machine.
IMG_2758.JPG
 
Ahhhh. Slot 15 M835 or the later M8350 is the posibus card. This box had Posibus peripherals at one time. And if it had the M8360 in Slot 10 that would also have allowed one Data break device.

As an early serial number unit (318 from 4/25/1971) there would not have been many omnibus peripherals when that machine was new. So it most likely had 8/i period peripherals. TC08 (DECtape) or DF32D. It was also possible to put a posibus to negibus converter and use the even older negibus devices as well.

For the TD8E to be the system device on OS/8 requires quite a lot of additional stuff. It can be a non system device with just a 2 page handler. There is bunch of stuff needed to make it convenient to boot from.

Very interesting. Wouldn't it be fun to know what it was used for?
 
Hm. Was the posibus card bi-directional (ie could I stick one in an Omnibus and have a pdp8/l access things?)
 
czunit said:
Hm. Was the posibus card bi-directional (ie could I stick one in an Omnibus and have a pdp8/l access things?)
Click to expand...
You need a DW8E-PC Omnibus Expansion Chassis to do that. We have one in a PDP-12 that connects the Posibus from the PDP-12 to an Omnibus chassis that holds an RX8E, KR8F, and PC8E.
 
The M8350 allows the Omnibus to communicate with Posibus peripherals, but not already attached to a Posibus computer like an 8/I. You only need one M8350 for a number of peripherals.

However, if your peripheral is a data break device, you need an M8360. In fact, you need an M8360 for each data break device on the bus, as I understand it.

The DW8E, which allows a Posibus to interact with Omnibus peripherals, only supports one data break device in the DW8E, as I recall.
 
antiquekid3 said:
The DW8E, which allows a Posibus to interact with Omnibus peripherals, only supports one data break device in the DW8E, as I recall.
Click to expand...
There are two separate Omnibuses in the DW8E-PC chassis if you install all of the bus driver boards. Then you can have two Data-Break devices in the chassis.
 
The M835 board was not in the machine when I got it.

The machine has been a controller to a cutting machine of PCB photo masks at a Swedish company called ASEA (that later became ABB). Then it was sold to Chalmers University in Gothenburg. In 2008 it was auctioned out on Chalmers ham radio clubs (ETA) yearly auction. Someone actually filmed the auction and put it on Youtube
 
I have 5 of the M8350 boards. It is the most common quad omnibus board in my collection even though I have never intentionally purchased one and have no Posibus peripherals to use them with. They just seem to show up in machines or when I bought a collection of boards. And I don't have any cables for them even if I did have some Posibus peripherals. If you are in the US and NEED one of them, let me know. At the moment I am treating them as a potential source of spare IC's. If you have an actual use for one I would let one go for $50 plus shipping.

Oh, I guess I misspoke as I have 8 of the M8317 option 2 boards which are hex width boards out of PDP-8a machines but those were partly intentional purchases in order to get all the different boot ROM versions. Several of these are in poor condition so they are spare parts donors at best.
 
I'm in Sweden, overseas. I don't feel that I have any use of a M8350 more that for adding one in the collection... I guess that frieght will be more then $50?

Are there that may different boot ROM versions? In the little 8A that I use for lab purposes I have serialdisk boot ROM's.
 
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anders_bzn said:
Are there that may different boot ROM versions? In the little 8A that I use for lab purposes I have serialdisk boot ROM's.
Click to expand...
There are several different boot roms on the M8317. I don't remember how many, three or four at least. And several different dip selectable in each one of those. How did you get the serial disk boot into the M8317? I have some unburned parts but they are single use and I have not needed to burn a set yet.
 
It's well documented how the ROM's work so I just took the binary file of the serialdisk boot loader an parsed it and burned two ROM's. I wrote a litte C-program that does the job. I also wrote a program that takes to ROM-dumps and creates a list file with the boot code and the different command (load address and start commands). The programs are on github and now I just added the different ROM's that I got, including the serialdisk ones. https://github.com/anders-bzn/pdp8-tools
 
anders_bzn said:
It's well documented how the ROM's work so I just took the binary file of the serialdisk boot loader an parsed it and burned two ROM's. I wrote a litte C-program that does the job. I also wrote a program that takes to ROM-dumps and creates a list file with the boot code and the different command (load address and start commands). The programs are on github and now I just added the different ROM's that I got, including the serialdisk ones. https://github.com/anders-bzn/pdp8-tools
Click to expand...
Thanks for that! Someday I will verify my stuff with yours.
 
Very many things started to work, I have tested CPU, console, KL8E and the extended memory control in my 8A. 10-slots with a KK8E is little weird. Now I have enough working pieces to start to rebuild the 8E in it's on chassie. Only one thing is untested, the memory of cause. This repair has gone much faster than I expected. I only had to replace lightbulbs on the frontpanel.
IMG_2764.JPG

The serial board, I temporarly changed the device address to 40/41 and modified it for RS232 instead of current loop (crystal, remove filter capcitor and baudrate). I also made a little PCB-cable assembly for replacing the BC01 cable. Wanted to have something more lab-friendly. On github: https://github.com/anders-bzn/BC01
IMG_2757.JPG

I also tested the PSU under load. I had to replace on fan that was mechanically stuck.
IMG_2767.JPG
 
anders_bzn said:
Very many things started to work, I have tested CPU, console, KL8E and the extended memory control in my 8A. 10-slots with a KK8E is little weird. Now I have enough working pieces to start to rebuild the 8E in it's on chassie. Only one thing is untested, the memory of cause. This repair has gone much faster than I expected. I only had to replace lightbulbs on the frontpanel.
View attachment 1285363
Click to expand...
Is that front panel on an extender plugged into the 8/A backplane? Not sure that I understand what I'm seeing here :-{!
 
pbirkel@gmail.com said:
Is that front panel on an extender plugged into the 8/A backplane? Not sure that I understand what I'm seeing here :-{!
Click to expand...
Yes, it's on an extender. But you can't se that since I have put the fronpanel plastic on top. To get it to work, you also need to supply -15V and +8V on the flat pin connectors on the side of the board. This to unlock panel lock and light up the bulbs. Those are normally connected directly to the PSU
 
anders_bzn said:
Yes, it's on an extender. But you can't se that since I have put the fronpanel plastic on top. To get it to work, you also need to supply -15V and +8V on the flat pin connectors on the side of the board. This to unlock panel lock and light up the bulbs. Those are normally connected directly to the PSU
Click to expand...
Thank you for the explanation. What was the benefit to using this configuration with both front/control panels in play?
 
I always wondered if you could plug an E front panel into an A chassis with an A front panel connected. It looks like it does work! What I am questioning is why the displays are not showing the same thing. The E panel shows the MD as 6232 and the A shows it as 232. What am I missing?
 
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