I managed to buy a 'reconditioned' BA23 power supply for my microPDP-11/53. The model number is H7864-A ... some of them seem to be often listed as HP parts, I guess HP now own the rights to all the old Digital stuff. It was delivered today and I installed and tested it. It looked brand new, there was no dust inside. Here I am measuring the 12 volt supply:
This is a switched mode power supply, so it won't show a voltage unless there is a load attached to it. So I have plugged in an old CD-ROM drive to give it something to do. The 5 volt supply measured at 5.08v, and as you can see the 12 volt supply showed 12.11v. The supply voltages were stable during my tests. Here I am getting everything ready to do the tests:
After I did these tests several times and took all the pictures the power supply went bang and gave out a cloud of smoke. Like before, I think that this is a big capacitor on the incoming supply that has exploded. I was quite surprised since the unit was in such good condition and was sold as 'reconditioned'. However, it still seems to work, even after all that. Maybe they are all going to do this - they are quite old afterall.
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:
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:
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:
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.