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PDP 11/23 restoration

A

Agent86

Member
Joined
Aug 28, 2021
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Location
Beech Island, SC
A friend just gave me a PDP 11/23. It hasn't been powered up for 10 years. I'm kinda new to vintage computers. I was designing computers about the time this PDP was built. Back then we called it a computer - not vintage. I really don't know where to start. It's just the CPU - no disk drive. My friend said it would boot up. I don't want to plug it in until I've gone over everything. He also gave me a VT 220 terminal. No serial cable. I'm not sure how to identify all the pieces. Where do I start?
 
Working on the pics. The boards with M numbers are M8186, M8059KF, and M8043. There are 2 large boards without M numbers or the burgundy tabs.
 
M8061 and M8012 for the large boards with cast metal.
wondering if any of this indicates when the unit was built. Still trying to post some pics.
 
What documentation identifies the pin out of the serial ports? I’m assuming RS-232. Probably have to get an RS-232 to USB adapter, or repair the VT -220 I got with it. No cables were supplied.
 
Agent86 said:
M8061 and M8012 for the large boards with cast metal.
Click to expand...

M8012 Q-Bus terminator, 6 ROM sockets. Usually holds bootstrap and diagnostic ROMs
M8061 RLV12 RL01/RL02 Disk Controller, 22-bit

That makes a nice system for running the RT11 operating system from an RL01 or RL02 disk drive.

You can look at the date codes on the ICs to get an idea of when it was made. The date codes are usually a two digit month and a two digit year. You will usually find that most of the date codes on a board are within a few months of each other.
 
Nice a PDP1123, I have also.
First Notice the setup, The card sequence is critical.
Than take out all cards and first make sure your power supply is working safe and proper.

Than read about M8043 DLV11-J 4x serial ports.
1 is the console port, this is the port to attach your VT220 and to control the CPU.
Read about the trappings to find out if the console port is indeed strapped as console and attach your VT220 at it.
Just a serial cross cable will do.
Find out the Baudrate settings on that M8043 card and type Set-up key VT220
tabb to COMM and set all according the card settings.
Remember to use also settings EAI communications(RS232 port), Transmit=Receive, 8bit 1 stop
Use the most right enter key at the keyboard to select, "middle" enter will not work in Setup.
Find in the setup also the SAVE option so next time VT220 starts with these new settings.

Other ports can be used to f.i. attach a laptop with TU58 simulation and as you Bootstrap your ROM at to BOOT TU58 you can
that way load a system operating.

Well for later, first check the basics.

Find in this Forum about starting PDP1123, I also wrote some setups.
 
MauriceH said:
Nice a PDP1123, I have also.
First Notice the setup, The card sequence is critical.
Than take out all cards and first make sure your power supply is working safe and proper.

Than read about M8043 DLV11-J 4x serial ports.
1 is the console port, this is the port to attach your VT220 and to control the CPU.
Read about the trappings to find out if the console port is indeed strapped as console and attach your VT220 at it.
Just a serial cross cable will do.
Find out the Baudrate settings on that M8043 card and type Set-up key VT220
tabb to COMM and set all according the card settings.
Remember to use also settings EAI communications(RS232 port), Transmit=Receive, 8bit 1 stop
Use the most right enter key at the keyboard to select, "middle" enter will not work in Setup.
Find in the setup also the SAVE option so next time VT220 starts with these new settings.

Other ports can be used to f.i. attach a laptop with TU58 simulation and as you Bootstrap your ROM at to BOOT TU58 you can
that way load a system operating.

Well for later, first check the basics.

Find in this Forum about starting PDP1123, I also wrote some setups.
Click to expand...

The M8043's serial ports are numbered 0 - 3 with 3 being the default console port. Note that if you need more than 3 general purpose serial ports you can include a second card and strap port 3 on the second card as a general purpose port.

A guide to strapping the serial protocol and other options is here:

https://usermanual.wiki/Document/DLV11JConfigurationGuideM804

Something to keep in mind if your M8186 has the MMU option, addresses entered into test programs will be 16 bit virtual addresses.

But when entering the same address via ODT, for example to load an ASCII character into a serial port's xmit buffer, you will need to enter the full 18 or 22 bits of a physical address depending on the address width of the system, probably 22 bits for your system.

http://web.frainresearch.org:8080/projects/pdp-11/dcf11.php.

That has bit me on the behind more than once if I've been away from the system for a while.

I would just add, verify & don't assume. DEC had many variations of their Qbus backplanes. Not all cards will function in any Qbus slot. It is possible to damage things if for instance you plug a card into a slot where it fits but doesn't belong. After you've checked out your power supply, determine what type of backplane you have. People have been known to get a system with the cards in the wrong slots, assume that what they received was a working configuration, and blow things up in the process.

This would be a good place to start:

http://bitsavers.informatik.uni-stu...EB-24944-18_Micro_PDP-11_Handbook_1983-84.pdf
 
Thanks for all the information. I’ll be busy this weekend. A little concerned by this stain that is coming from under the power supply. Will have to check that out.
 

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At some point, you'll want to take a peek at your backplane, to see what model you have.
That will tell you how many bits you can address. . . . 16, 18, or 22. . .
The H9270 was typically 18 bits, but could be readily modified for 22-bit / 4MB memory support.
The H9276 (and H9275) backplanes are 22-bit.

Bitsavers has various manuals in these sections -

http://bitsavers.org/pdf/dec/pdp11/1123/

http://bitsavers.org/pdf/dec/pdp11/1103/
(The 11/03 is a bit older, but you can still sometimes
glean tidbits of information that are helpful.)
 
I'm excited and happy to report that the PDP-11/23 and VT220 are alive and working. I removed all the boards and disassembled the keyboard then washed in the dishwasher. Cleaned everything else the best I could. Reassembled after confirming power supply operation. At first I had my serial cable miss-wired, was counting pins on the M8043 10 pin connector from left-to-right - 1,3,5,7,9 instead of 9, 7, 5, 3, 1. Glad that doesn't seem to have caused any lasting damage.

Next I've got to learn how to use the console and ODT. I did copy in a simple program I found on the web. Eventually I was able to run it as advertised.

Then I'll work on mass storage. Emulation of either an RL02 or TU58 seems to be the viable alternatives. I'm keeping an eye out for original equipment, but that doesn't seem feasible right now.

Many thanks to everyone who commented. I studied all your responses and downloaded the referenced material. All very helpful.

Any suggestions of what to do next are greatly appreciated. What is the most fun thing you've done with your PDP?
 
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