DECstation 5000/240 With the TURBOchannel Extender

Recently I repaired the H7826 power supply in my TURBOchannel Extender. So now I wanted to get it working with the DECstation 5000/240 it came with. The trouble is, I don’t have the cable to connect the Extender to the DECstation. However, I found a 100-pin SCSI cable that works for connecting the two enclosures.

The TURBOchannel Extender also has a SCSI connector for the disks and the CD-ROM Drive. To use the SCSI devices you have to connect a separate cable. The TURBOchannel Extender cable is just used for TURBOchannel cards. In messing around with the TURBOchannel Extender I found that if I install a PMAD (network interface) card in it, this seems to prevent any other card installed in the Extender from being recognised. I have not worked out why.

I have now configured the machine as follows. In the main DECstation enclosure I have installed a PMAG-D (actually upgraded to PMAG-E as it reports a 24-bit depth, the D is only 8-bit), and TURBOchannel Extender option. In the TURBOchannel Extender I have installed just the video capture card, which Ultrix does not recognise (not surprising as I think it is an experimental card), and the RRD42 CD-ROM drive and the two RZ25 drives that came with the machine.

Sadly the RRD42 does not seem to work. It will take in a caddy and eject it when I press the button, but I have been unable to use it to read any CDs. This will have to go on my list to look at some day.

I installed Ultrix 4.5 on one of the disks that came with the Extender. Sadly the other disk gives hard error if I try to install to that one. So I now have Ultrix 4.5 running on the DECstation, using the Extender as it was intended. The TURBOchannel Extender cable is a bit redundant though as the only TURBOchannel card in it is not supported by Ultrix. I have NetBSD 1.5.3 on a SCSI disk in a Storage Expansion enclosure, I can’t really put this disk in the Extender because it is too big.

Unfortunately I do experience intermittent startup problems. Sometimes the LEDs will indicate a “memory slot 0 could not be initialized” error. Cycling power seems to resolve this.

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H7826 Power Supply Repaired

After a spell of concentrating on other things I have finally got round to looking again at the H7826 power supply from my TURBOchannel Extender. When I left it back at the beginning of the year I was waiting for parts for the 5019572 daughter board which controls the switching transistors. I posted the details here, including a schematic of the daughter board.

Once I had replaced the parts on the 5019572 daughter board I bench tested it in isolation. I had to make sure that Vcc was above the ON threshold which is between 15V and 17V. The board drew what appeared to be a reasonable 20mA and the 555 started oscillating. So I reinstalled the daughter board.

With the 5019572 daughter board back in place I found that the 555 was not oscillating. This was because its Vcc was 0V. It looked like there might be a blip on Vcc when applying power, but I don’t have a DSO so I couldn’t be sure. Checking Vcc for the daughter card as a whole I found that it went up to about 15V on applying power, but then it almost immediately dropped to 0V. After removing power it stayed at 0V for a bit before jumping back up and finally decaying slowly.

This told me that the daughter board was either receiving a shutdown signal or it was sensing an overcurrent. A bit more probing showed that it was the shutdown signal. I traced this to another daughter board on the secondary side, labelled 5019574.

I removed the 5019574 daughter board and reverse engineered its schematic, which is reproduced below:



I tested the board’s current draw on the bench at 5V and it looked OK. While I was at it I also reverse engineered the schematic for the 5019576 daughter board, which is right next to it, as they are both involved in monitoring for shutdown conditions. This schematic is reproduced below:


None of the parts on these two daughter boards appeared to be bad. I did replace the LM393 on the 5019576 daughter board because during testing it had appeared to get hot, but I later realised I had made a mistake with how I had connected up the board, so I may have replaced it unnecessarily. However the PSU still would not work, the fans would twitch on applying power and that was all. One of the electrolytic capacitors on the 5019574 board had measured a bit high on ESR, and it was also looking a bit brown as if it had been subjected to a lot of heat, so I replaced it. But still the PSU continued not to work.

Then I realised that I could not trace one of the tracks connecting the 5019574 daughter board to anything on the main board. The track was visible but did not seem to be electrically connected to anything. I noticed corrosion on the track (this power supply is not in the best condition). I asked a couple of friends who have this power supply to confirm where this track went. Once I knew where it was supposed to go, I soldered a wire to the back of the main board to replace the broken track.

H7826 Repair of Corroded Track

Wire to replace a corroded track

This seemed to do the trick! I connected a load module from a MicroVAX 2000 and now the fans spin and there are voltages on the outputs. I checked the ripple on the 5V and 12V outputs and that was good. The LED does not seem to work, but the PSU powers up a hard disk and a PMAD-A card installed in the TURBOchannel Extender, so I think it is all working.

Now I need to find a cable to connect the TURBOchannel Extender to the DECstation 5000/240. I have found a 100-pin SCSI cable which fits but I don’t know if the pinout is correct so I dare not try it.

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Flocoder FLIP Now Processes Its Own Source

I am at the stage with my MUSS restoration that I can process the Flocoder FLIP source code with my own implementation of FLIP written in Flex and Bison.

My MUSL compiler can’t process all the Flocoder source files yet though, for a couple of reasons.

The first is that some of the source files appear to have too many END statements. I need to look into this to see if my understanding of the grammar is incorrect. However, these problems occur in files that I don’t think I need in order to re-create FLIP, so I will defer investigation. I may hit problems again when I try to build the MUSL compiler sources.

The second is that there are some elements of the syntax that are context-sensitive and can’t be parsed with Bison without some additional work. There are actually a couple of areas where this does not currently work. First, one of the Flocoder modules declares both a type and variable with the same name. The second is where addresses of procedures are declared, these create a syntax ambiguity which needs additional semantic processing. These problems are solvable, but I have not looked at them yet.

My next steps are to start generating C code from MUSL, but I think that to do it correctly I am going to have to resolve the context problems mentioned above.

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Flocoder Flip Progress

I haven’t been doing much in the vintage computing arena recently, but I have finally got around to finishing off my crude implementation of Flip. The source code is up on GitHub.

My first attempt didn’t work very well. I was not ordering the boxes well and produced invalid MUSL because I used too many labels and GOTO statements. In the end I decided to reverse engineer the original Flocoder source for Flip. I created textual versions of some of the critical charts, you can see them in the source code (doc021 and doc031). The control structures represented by the charts didn’t look too easy to turn into normal structured code without GOTOs, so in the end I decided to take the easy path and code it with GOTOs just exactly as represented in the original Flip source charts.

My version of Flip can now take doc031 from the source code and produce the MUSL source from it. Furthermore, my initial MUSL parser is now able to parse the output from Flipping doc031, without any hand modifications to the Flip output.

The next step is going to be to try processing the other doc files and check that my parser can parse them all. After that I will try to get my MUSL parser to produce C code, so that I can generate a program that implements Flip from the Flocoder source.

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MUSS Source Code Now Available

I have received qualified permission to publish the MUSS source code that was recently recovered, as free and open source software. It is available here.

I have also made a bit of progress on the MUSS restoration. My implementation of FLIP is improved but still not quite there yet. I also have a parser for MUSL, which parses the output of my FLIP implementation for one of the FLIP source modules, with a little hand modification before parsing it.

I have created a page on MUSS where I will report more about MUSS and its restoration.

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I have now got a crude implementation of the Flocoder Flip program written using Flex and Bison. It can take a Flocoder file from the MUSS sources and extract what I hope is compilable MUSL code. The code is on GitHub.

I am not 100% sure that the code is valid as I have taken a very naïve approach to the code generation stage. Every BOX except the start box is labelled, and every BOX ends with a jump to the next box in the FLOW sequence. It does not attempt to merge consecutive BOXes.

However, I am hoping that this is enough to take the original Flocoder source for Flip and turn that into MUSL that I can then compile. The next step, which I have just started, is to create a MUSL to C compiler that will generate C from the Flocoder source for Flip, so I can get a version of Flip working in C. If I can do that then I should be able to process the Flocoder files using the proper code for Flip and compiling those to C as well.

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MUSS GitHub Project

For anyone who wants to follow the effort to revive MUSS, I have started a project on GitHub. You can find the repository here. The initial effort is focussed on creating FLIP to translate the Flocoder to compilable MUSL and I have made a start on that.

Once I have FLIP then I will need to start the process of compiling MUSL. I will probably compile the MUSL to C and then compile the original MUSL compiler (written in MUSL), but that is a little bit further off.

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