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PDP-8/A, My First PDP computer

A

Atari26003

Experienced Member
Joined
Feb 21, 2008
Messages
74
Location
Ontario, Canada
Hello DEC world! I finally after few months of back and forth emails was able to get my hands on a PDP-8/A system. Upfront this post may have silly questions or statements but please keep that in mind as I am just starting to get into this lovely world. If you don't enjoy reading stories I sum everything up in the TLDR portion!

Story:
I was browsing Google groups and noticed somebody posting saying they had a PDP-8/A ( believed to be a 600) and it was looking for a new home. The post was a few months old but I figured I would try and luck has it he still had the system, with part of the device ( Unknown at the time ) hooked up to it . After agreeing on a fair price to me. I paid hoping to get the PDP-8 in one piece along with the unknown unit that went along with it labeled as nothing but a " VG " system. I later found out this unit was used in a lab hooked up to a Spectrometer. This was a pretty blind buy and I honestly expected a beat up system to show up at the drop off location or if I was unlucky enough to not have anything at all. But I did find 1 of the 2 packages arriving at its destination. The VG unit nowhere to be seen for almost 2 months I couldn't wait any longer so I just went and picked up the PDP-8 itself.

TLDR:
Blindly bought a System off google groups, guy turned out be very nice and sold me it at a fair price. Was supposed to be the system and the VG unit ( part of a spectrometer) ( With another backplane too! ) but that never showed up and we lost contact with each other ( Which I guess is fine seeing as I finally have my hands on one of these).

Unpacking the system I did find he packed it amazingly well with slits of cardboard between each of the boards. I did have some casualties however such as a plastic mount on the back of the bottom faceplate of the unit is broken, and I have two extra nuts and a clip ( Going off topic again).

I have created a Gallery and I will update here and add images to it to show progress made.

http://imgur.com/a/Nvj9x

I did some googling on the cards inside my machine and I am curious in this current configuration is it possible to have it boot for a simple test of everything I don't want to have something missing that is crucial.

Current Configuration of PDP-8/A:
M8317 - PDP-8/A bootstrap, powerfail (hex wide)


MEMORY COULD BE ONE OF THREE ( Need to examine next time I am home)
M8417 - PDP8A 16K MOS Memory (hex wide)
M8417 MSC8AB PDP8A 32K MOS Memory (hex wide)
M8417 MSC8DJ PDP8A 128K MOS Memory (hex wide)


M8316 - PDP-8/A I/O serial/parallel/clock (hex wide)
M8320 - Bus loads
M8330 - Timing board, replaces M833
M8300 - Major registers
M8310 - Major register control


My future hopes for this system.

I hope to load an OS/8 or similar operating system to the beast and mount it into an official DIGITAL cabinet along with a paper tape reader.

Thanks for looking,
Matt
 
Hi All;
Atari, I know almost nothing about PDP 8's..
So, I would say Congratulations..
Based on my Knowledge of a wide range of Machines..
I would Check out the Power Supply, Especially the Capacitors.. Since they are Old and possibly Leaking, they Could Blow something up, If you apply Power to the machine..
So, Don't Just Plug it in and Hope for the Best..
At minimum Use a Dim Bulb Tester (that You could very easily make, and also a Variac..
But, before Doing anything, Take the Power Supply Apart to Have a good look at it, and do a resistance Measurement of the Capacitors.. That will give You some indication, of their condition.. If they show a continuous Resistance Reading than most likely the Cap is bad..
AND NEEDS TO BE REPLACED !!!!!
Look for Burnt parts and Do a thorough check of Everything..
Then You can use the above items and try it out, with NO Boards in it at all, Including Diss-attaching power to the Front Panel..
OtherWise You are asking for Trouble.. Ask me "HOW" I know..

Here are a couple of links that Might be of some Help.. Also, these are For Old Radio's and Old TV's, but the Principles are the same.. As, far as plugging in Something..

https://www.youtube.com/watch?v=xF15sv41AEY

https://www.youtube.com/watch?v=pnEwtMCXDA0

https://www.youtube.com/watch?v=UH45YdmQUn4

These are from two of my Favorite Guys for Working on Old Radio's and TV's..

THANK YOU Marty
 
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It looks like a good system, and it does have the 8/e central processor.

It is possible that the M8317 may have the correct roms to perform a limited test on startup. You will need to tell us what is stamped on the tops of the socketed ICs on the M8317 (as well as their locations.) Otherwise, you can key in any number of test routines from the programmer's console.

There was a fellow on here, Adrian, from western Canada who retreived an 8/a from a large spectrometer a few years ago.

You will need some mass storage to run OS/8. At the moment, you'll have to either key in programs by hand into the programmer's console, or load them over the console terminal port from emulated papertape. There is a fellow Paul on cctalk who may be able to help you find a disk controller and floppy drive perhaps.

Lou
 
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Lou - N2MIY said:
You will need some mass storage to run OS/8. At the moment, you'll have to either key in programs by hand into the programmer's console, or load them over the consoler terminal port from emulated papertape. There is a fellow Paul on cctalk who may be able to help you find a disk controller and floppy drive perhaps.
Click to expand...

You can also obtain, generally quite cheaply (especially compared to a disk drive and its controllers) a spare serial card and use SerialDisk to boot OS/8.

Best of luck with your 8/A! Looks like a fun project.

Kyle
 
Start here:

http://bitsavers.trailing-edge.com/...01-OP-002_PDP-8A_Operators_Handbook_Sep76.pdf
http://bitsavers.trailing-edge.com/...2_PDP-8A_Miniprocessor_Users_Manual_Dec76.pdf
(If you don't know about bitsavers.org, take a look around. Bitsavers (courtesy of Al, the curator) will become your best source for bedrock technical info)

These two manuals include descriptions of the various PDP-8/A configurations and as well as several short tests that can be run from the front panel without requiring any other input device.

Marty's caution about power supplies and capacitors is well founded - be sure to check voltage levels and power ripple before going to far. I recently was stymied by a machine that showed good DC voltages but was floundering because of undetected AC ripple on the DC rails.

Nice way to start the New Year!

Jack
 
Hi All;
JackRubin, THANK YOU.. "" Marty's caution about power supplies and capacitors is well founded - "" I thought I had been barking up the Wrong Tree..
So, after You have made sure things are working fine, Start Running some short Test programs and Please, let us know how You make out..

THANK YOU Marty
 
I apologize on such a delayed update Life and work have consumed so much of my time it took until now to be able to get the time to update this post. This passing week I took the time to look through and patch up the power cord as well as taking a closer look at the power supply. From my understanding everything seemed in order now.

I did not wish to leave the power supply without a load ( I have heard stories that they don't appreciate that ), So I attached some of the older VG cards that I had from when it was hooked up to that mass spectrometer ( These cards to me personally would take the heat rather than a valuable board). After putting a single card into the card cage I was able to flip the main power switch on the rear then the one on the limited function panel and it WORKED!!!! . I was having a discussion with a friend who was helping dig through documents while I was trying to get the cards properly placed in the cage ( This has to be one of the toughest card cages to insert cards into), I replicated the original setup when it arrived at my house minus the Extra "VG " cards .

From this point I was able to boot up the machine and use the operator’s panel with success. I first just loaded random things into memory to see if they would take and when that DID work my friend dug up a little program that could just count in a loop and display it on the panel ( I can provide this program if someone is looking for it, I just have to find that chat log. I included an 8 second video (thanks MMS) of it successfully counting and pictures to show the great amount of work that I have from this point.

Updated IMGUR gallery
This picture of the cage displays how much damage was done during shipment (Could this be any more frustrating?) I apologize for the wretched quality I still am unable to get myself a proper camera and apartment living makes work areas very tiny.
http://i.imgur.com/cCoLzKO.jpg

This second image displays the computer when it was online and running the counting program.
http://i.imgur.com/3FqgRjg.jpg

This is the great 8 second video of the program thanks to MMS limitations.( will be updated with another video that is better later)
https://youtu.be/pN74WNt-xb0



The Question Section

The next step since I believe all should be in working order is to get a serial connection working. I currently in my configuration have the M8316 Option board #1 in the cage. This should if I make a connector by hand work for a serial terminal should it not? or at least an RS232?? I know when I google I come up with the board M8650 to be using for this. Board Info If not I have heard of this project called OMNI-USB which has video's on YouTube a website and a shop link (That is under construction for past little while) would be my other option. Has anybody on this forum used this product and is it worth investing into?

The reason I ask is because it is either this or try to now find how to hook up a serial terminal to it (I have a Dec VT510 a few steps from it if this could be possible).



The next two questions would be simple which forms of mass storage should I be looking at attaching to the computer and secondly has anybody ever used a time sharing operating system with the PDP-8 of any type before? I have heard of MULTOS/8 & TSS-8 (but I have no idea which would be the better option if anybody with experience would just say which one to try).

Thank you for your time!
-Atari
 
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Now's the time to go back to the PDP-8/A Operator's Handbook on bitsavers. This short manual walks you through setup and configuring the M8316 serial port, the expected console for this machine, as well as providing several useful test programs. You can find info on building serial cables here - http://homepage.cs.uiowa.edu/~jones/pdp8/hard8e/bc01v.html - the same cable is used for the M8316 and for the M8650, so you might as well build a couple of them! Lots (relatively speaking) are very happy with Kyle's SerialDisk for mass storage; it runs very nicely with a souped-up M8650.

Some careful work with two-by-fours and C-clamps could go a long way towards straightening out your chassis and would probably make card insertion a lot easier.

Where are you in Ontario? There a several DEC collectors in the greater Toronto area. Maybe you'll consider coming to VCF-East in Wall Township, NJ on April 17-19 or VCF-Midwest later in September.

Jack
 
Matt,

On my 8/a built from parts, I made the cable that connects to the M8316. It was easy and that is the route you should go. If worst comes to worst, I can document all the switch settings on my M8316 for you to start from.

As for an operating system, OS/8 is what you will eventually run.

As Jack wrote, at this point you need to look for an M8650 or M8655 to run Kyle's mass storage emulator. This is your quickest path to success.

Lou
 
The next two questions would be simple which forms of mass storage should I be looking at attaching to the computer and secondly has anybody ever used a time sharing operating system with the PDP-8 of any type before? I have heard of MULTOS/8 & TSS-8 (but I have no idea which would be the better option if anybody with experience would just say which one to try).
Click to expand...
I ran MULTOS/8 on my 8e a few times. Never really had a need for it and I only had one terminal. I wanted to run TSS/8
on my 8i but without an RF08/RS08 or DF32 type drive it's much harder since it expects that type of disk. I'd love to
see an RK05 driver for it.
 
Plus you can change your boot ROMs to boot to OS/8 from serial ;-)

Plus you can change your boot ROMs to boot to OS/8 from serial ;-)

m_thompson said:
You can try the toggle-in programs to see if everything is working OK.
http://www.pdp8online.com/pdp8cgi/query_docs/view.pl?id=188

With two serial ports installed, you can use Kyle's serial RK05 emulator and run OS/8.
https://github.com/drovak/os8diskserver
Click to expand...

I'll second this as a quick way to get OS/8 running on my pdp8/a I have my console running on the default serial of the m8316 card, and added a m8655 card to run Kyle's excellent serial disk server.

With some monkeying around with gal22v10's I was able to make some boot ROMs that boot OS/8 from a raspberry pi connected through a usb to serial adapter. (I guess I should document this).

I spent forever trying to reliably boot OS/8 from my rxo1 drives...but this works. If there's a choice of m8655 or the earlier m8650, go with the m8650 it can be rigged up to 'modern' serial speeds. The m8655 is stuck to 19.2k baud tops.

Cheers,
Crawford
 
Hopefully at VCF this year

Hopefully at VCF this year

jackrubin said:
YES, PLEASE!!

Will you be at VCF-East?

Jack
Click to expand...

Jack,

Yes, I hope to be there Sunday morning the 19th. I got roped into judging a STEM programming contest before I knew it was a conflict with VCF Saturday.

-Crawford
 
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