microPDP-11/53 - you win some, you lose some

After some fiddling and consulting of the KDJ11-D (CPU card) manual I've come to the conclusion that the message I was getting is nothing to do with boot failure, but a failure of the RAM chips on the board.  If I start the machine with the HALT button pressed I can get into ODT (Octal Debugging Technique) and this should let me set values in memory directly.  You just type the memory location and a forward slash / and the system tells you what is in memory there.  You can then enter a new value.  Typing the same location again with a slash should give you the value you have just entered.  However, with my machine the values I put in seem to get garbled.  This is a real setback, since my soldering skills are not good enough to replace all these RAM chips (there are 54 of them).  But still I have found out a lot about ODT, and that is a good thing.

However, I can ignore these memory errors by pressing <CTRL+O>4<Enter>, this allows you to carry on regardless.  So I installed the RQDX3 disk controller in slot two of the backplane and started the machine again, this time ignoring the RAM error and attempting to boot, but without a disk drive installed.  This time you would expect a different message - I imagine that it should find the disk controller but complain that there is no disk drive.  Here is the transcript of what I got:

KDJ11-D/S   4.55
Error, see troubleshooting section in Owner's manual for assistance
RAM    VPC=024454  PA=17604454  00000000/104676 <> 177776

KDJ11-D/S> 4

Commands are Help, Boot, List, Map, Test and Wrap.
Type a command then press the RETURN key: BOOT DU0

KDJ11-D/S   E.11
Drive error

Commands are Help, Boot, List, Map, Test and Wrap.
Type a command then press the RETURN key:

Not bad!  It looks like it does indeed find the RQDX3 card and attempt to boot.  If I install my RX33 floppy disk drive, I wonder if I'll get a slightly different message?  That's got to be the next thing...

microPDP-11/53 - inventory

For reference, here are all the parts that I have managed to scrounge together for my microPDP-11/53.  These parts were bought from a single seller found on eBay:

- microPDP outer case
- BA23 mounting box
- M7554 KDJ11-D/S CPU Card with onboard RAM
- PDP-11/53 backplane
- 2x power supply units for the BA23 (H7864-A)
- PDP-11/53 Front Display Panel
- M3107 8 Line Async Comms Card
- M3104 DHV11 8 Line Async Quad Card
- PDP-11/53 Console Panel (accepts MMJ cables)

Following that, I also managed to buy these from an IT parts supplier:

- Reconditioned power supply unit for the BA23 (H7864-A)
- Refurbished RQDX3 disk controller card
- Refurbished RX33-A floppy disk drive (1.2Mb)
- New MMJ socket to DB9 female serial adaptor H8571-J
- 2x 6 foot MMJ cables BC16E-6H

microPDP-11/53 - it lives!

After further tests of the power supply to make sure that the 12v and 5v supplies are stable, I decided to install the CPU card and try to fire up the machine.  I'm pretty sure that I have got all the cables in the right places and the right ways round.  I originally used an old RJ11 telephone cable to attach the console panel of the PDP to my MMJ to DB9 adaptor, and then to my PC.  The RJ11 cable I have only contains 4 wires, so the 2 outer wires of the MMJ connector (which has 6 connections) are not being used, but they are the RTS and CTS signals and won't be needed for a simple console.  The RJ11 cable I've used is crossed over so the TX and RX lines are crossed, which is useful.

The first time I switched the power on, nothing happened.  So I flipped dip switch 1 on the front control panel, which I think is for the Line Time Clock.  It was just a hunch.  However, when I powered it on again I got this message:

KDJ11-D/S   4.55
Error, see troubleshooting section in Owner's manual for assistance
RAM    VPC=024454  PA=17604454  00000000/124776 <> 177776

Pretty much what I expected, since the machine does not have any drives to boot from.  This is an encouraging start.  I'm on my way...

DEC microPDP-11/53 Rebuild

For some time I've been interested in getting hold of a DEC PDP-11, I find it to be an interesting piece of history since the C programming language was originally written on one. The first port of Unix was on a PDP-11. Anyway, I have just managed to buy enough bits to build a viable machine. I say 'bits' because I have not bought a working machine, but components taken from several machines. So I need to figure out how to put it all together.  Obviously this is one of the most recent versions of the machine from the 1980s, not one of the blinky light machines from the 70s.  Still, if I'm going to own a minicomputer this will fit easier into my house...

Anyway, the first thing was to put the backplane into the BA23 mounting box, the backplane also has a distribution panel attached, which exposes the connectors for the disk drives amongst other things.  Here is a start:

Starting to put the cables in

I have put the power supply in place.  But I have not worked out which way round the front panel ribbon cables go yet.  The cable which connects the power supply to the backplane seems to only go one way round which is helpful.  The fan was already in the mounting box, as you can see by the level of dust!  I also have attached the front panel:

The front panel

I have the outer enclosure that this mounting box goes inside, but have not found the cover that goes on the front yet.  I need to look for that.  This is a photo of the other side, showing the installed backplane:

The backplane

I need to keep working out where the cables go - and document their positions for future reference.  But my biggest problem so far has been the power supplies.  I managed to obtain two.  When I bench tested them, the first one went bang and threw out a cloud of smoke.  I believe that this was a large capacitor on the incoming power supply which exploded.  However, after that the power supply seemed to keep working.  The second power supply made strange chirping noises, but also seemed to work.  I think that it might be on its last legs.  I will need to get a stable power supply before I can switch it on.