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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Chris posted RX50 images of RT11 V5.3 on his site: Index of /pdp
I believe that you can use a 1.2MB PC diskette to write a physical RX50 from an image.
There are a few people trying to use a Gotek with Flash Floppy Firmware instead of a physical RX50 diskette drive.

disk0010 which is RT11 5.3 disk 1 RX33
disk0011 RT11 5.3 disk 2 RX33
disk0012 RT11 5.3 disk 3 RX33
disk0020 blank RX50 disk

The files in the Index of /pdp/xxdp directory contain XXDP images that should contain diags for your PDP-11. You can use them to make real diskettes.

disk0029 for a minimal RX50 XXDP 2.5
disk0000 for a minimal DU XXDP 2.5
disk0001-0008 is the full XXDP distro in RX33 format. Disk 1 is bootable.
disk0009 is a blank disk in xxdp format RX33

I’ve been doing some reading on making disks for the RX50 drives on a windows PC using a 1.2MB drive to write the SSQD diskettes.
All a steep learning curve

Hey Mike, I tried to write the DISK0029.IMG using PUTR on an old dos machine and was able to format an RX50 disk but the IMG file wouldn’t mount as XXDP in putr, but only FILES11, I imaged it onto a disk but no dice.

The forum topic that had the diskette images is here: Floppy drives for an 11/73 with an RQDX3. | Page 2 | Vintage Computer Federation Forums

The people on the DEC forum DEC | Vintage Computer Federation Forums are very knowledgeable and should be able to help more that I can. Maybe you could join the forum, post what you have done so far, and we can get a larger group of experts to help.

I’ve posted over and am awaiting approval for the thread.

In the meantime, if you could help me with models and photos of the card numbers and cables that would allow me to hook up an RL02 to a MicroPDP, I could start going through the 100s of disc packs to see for diagnostic, OS install and OS’s we probably have on them.

My concern is though the RL02s were probably hooked up to 11/34 40 70s etc that we have an not the QBUS units.

I’ll also look if with have an RX33 anywhere. We seem to have dozens of RX50s but I don’t recall seeing a single RX33 so far, which would probably make life simpler!!

An RLV12 (M8061) will work with RL01 and RL02 drives. An RLV11 (M8013) will only work with RL01 drives. You will need a bulkhead panel that connects to the ribbon cable to the RLV12. You need RL01/RL02 cables to connect the bulkhead to the first drive, and daisy-chain to more drives. The las drive needs a terminator installed.

The 11/34 etc. are Unibus machines and use an RL11 controller that will not work with the 11/83.

I have an 11/84 that uses the same CPU and memory as the 11/83, but has a converter to Unibus I/O.

I think it’s safe to assume that our racks of RL02s were more likely hooked up to real full 11s - we have about 7 drives daisy chained in three racks and terminator on the last, however there is no sign how the first units empty connector connected to anything - if you have a photo of the cable and bulkhead adaptor, it will make it easy for me to show and ask around for people to put it on our wanted list as we catalogue