Restoration : Micro PDP11/83


Yesterday myself and Greg were working to find a PDP to get online- to start the process of the over 20 PDP units we have and getting them running.

I personally have no experience with DEC beyond using some VT terminals I’ve the years.

It started out a bit of a flop with our racked PDP 11/34 stuck with PWR light only and no run - but assume this is a board issue as there seems to be parts missing.

The 11/04 powers and RUN comes on but can’t be halted.

So when we found the Micro PDP 11/83 I said, this is the one.

After about half an hour of trying to find comms cables to hook up a VT terminal, we finally realised wait- maybe there is an issue with a board. We opened it to find someone had disconnected the rear LCD and comms port! Gah!!

After that and some cable hopping we got the unit to an error screen over serial.

An error 61 and M8193 error

Working out how to change the clock speed is proving difficult. All the booklets I’ve read don’t make a lot of sense - and the command don’t work.

It seems we may have to take off the lid to put it in diagnostic mode before those command will work.

Originally I had the serial speed set to 9600 on “2” on the selector - now “8” which is supposed to be 9600 diagnostic - but clearly internal dips still need setting


Can you post an inventory of the part numbers on the boards that are installed?

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Serge joined Greg today and we corrected a 50/60hz dip switch and now the unit was able to boot into Micro/RSX OS.
The drive is on its way out so we need to clone it.

I’ve asked Serge to post the boards for you to look at, but there is seemingly 6 Webster hard disk controllers installed


Apologies if they are out of sequence, forum software wouldn’t let me do many of them at once.



On the DEC boards, the important information is the part number stamped on the metal PCB stiffener. Your CPU is probably a M8190-AE.

We are going to try and load up some alternative OS and software via a TU58 emulator from a PC today. Available at Github GitHub - AK6DN/tu58em: DEC PDP-11/VAX-11 TU58 drive emulator

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So Greg and I haven’t really got any further.
We have realised we can’t get out PDP M11/83 to recognise a second hard disk at DU1, but we have been able to get the Ethernet to work.

We need an M7940 serial card to allow connection to the PC laptop to emulate the TU58 as a boot device, but after looking for a while, we found one that was very old and didn’t have configurable DIPs.

Greg alerted me that the dips are needed to set the memory address.

I got this text from him later last night

“*Dang, that M7940 card in the 11/v03 is hard-coded to address 176500 and would have worked! *”

The card looked like it had got wet at some point so I think I’ll try giving it a clean in the ultrasonic bath first or maybe see if I can find a better example.

The M7940 has a larger 40/50 pin connector on it, that only needs 4 or 6 pins for serial comms so not sure why it’s so large- clearly must interface with several technologies.

Was look at the alternative to potentially Netbooting the PDP over its Ethernet card however have learned it uses what is a MOP server? A DECNet protocol that is Maintenance based- apparently Cisco iOS 15 still supports MOP and that it sounds like you need it for lots of stuff - I found a recent thread below but it seems this gentleman hasn’t got further on his MPDP11/93


You wouldn’t be willing to make us a set of PDP11 5.25” boot /install disks for a decent OS for the MPDP series would you?

We need a way to test and format some of our 5.25” MFM drives

I probably have the PDP-11 XXDP diagnostics diskette. If so, I will see if I can make a bootable copy of it.

I will also see if I can use PDP11GUI to make an image of the diskette.

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