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DEC VAX 4000-300 up and running

Posted <2020-09-14 Mon 19:36> by Aaron S. Jackson.

A couple of months before bnl passed away, he some how managed to put a VAX 4000 in my loft. It's a pretty big machine. Unfortunately the second time I turned it on, the power supply exploded. I looked into this quite a bit, and attempted to repair it on more than one occasion. Unfortunately the whole power supply is horrendously complicated to work on, because it all folds up into a cuboid. There were also a bunch of traces which has been eaten away by leaking electrolyte.

I have wondered for a while about whether I could replace this board with some external power supplies or small 12v modules. The broken board provided -12v, 0v and 12v, so I set about hooking up my power supplies to provide those voltages. I was a bit unsure about whether this was going to work because the power supply is quite complicated - I assumed it would detect the lack of 12v from it's output and shut down. Fortunately the VAX appears to tell the power supply whether it has its 12V rails, so the power supply stays quiet and doesn't complain.

I'll have to update this post at some point to include photos of how I extended the cables from the 12V power connectors on the back of the PSU.

First Power Up

Nervously I applied power. First the VAX' power supply, then the -12v rail, and then the 12V rail. Nothing happened. Ah well, that doesn't surprise me to much… It was worth a try…

I turned off the VAX PSU for a few moments and then switched it back on. It sprang to life, and I could see the CPU status decrementing as it went through its power on self tests. Wohoo! The next step was getting something displayed on the terminal. I wasted a huge amount of time trying to get this working with a USB serial adapter, but as usual these end up being a waste of time. Hooked up to the VT420 through a series of adapters, and there we have it, the power on self tests, one after an another.. Oh… Two failures?!

I found the manual online for the KA670 CPU. These two errors are SUBTEST_SF_0D and SUBTEST_5C_06. The first refers to the SGEC (Second Generating Ethernet Controller). The second is for the SHAC (Single Host Adapter Chip). I was able to get rid of the latter error by properly terminating the DSSI bus, but the ethernet one remains.

Once I set my terminal (correctly) to 8 bits, no parity, I was able to type and interact with the system. You can see below that it's able to detect the QBUS devices.

Playing around with that for a while until I realised the centronics sockets littered across the front of the VAX are NOT SCSI interfaces, but instead the weird DSSI stuff, and interestingly, an eight line serial interface board (DHQ11).

Cautiously I installed my spare Emulex UC07 SCSI controller and flashed a NetBSD miniroot to an SD card.

After some configuration of the Emulex controller, it booted into NetBSD!

Look at that! Setting an IP on the DELQA card worked and I can ping my gateway. I'm so happy to see this machine running, even in this weird state. I know bnl would have been happy to see this too.

The Future…

I intend to retrofit two small 12V modules into the power supply. This will make things look much tidier. The Emulex card can stay in the VAX, so I'll get a second SCSI2SD allowing my PDP-11 to have this one back. Finally, I need to do a full install of NetBSD so we can have some real fun. :)

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