• Please review our updated Terms and Rules here

Four-Phase Systems IV/90

I have a faint recollection that the bottom surface contain the servo-tracks, if so it becomes even more challenging, but it would also mean that it might be possible to recover all the data.

My own recollection and figure 3-17 in the reference manual suggests that it's the top surface of the middle disk that contains servo tracks:


The scratches that you saw - are they on the very bottom disk, or on disk 4-of-5 from the top? Because only the middle 3 disks contain data/servo.

Anyway, the work of Chris Fenton is interesting in case we'd ever have to archive a disk pack but we're unable to properly spin up the drive (the lack of servo could be one such reason):

 
Yeah I remember reading on his adventures back in the day to read that pack without the correct controller to run the drive. I have myself wondered how one would still retrieve the contents of a crashed pack by preventing one or more heads from loading but assuming it's not a servo track you have lost you would lose any date on the remainder of that surface.
 
During VCF MidWest I was gifted a set of five more boards from an IV/70 chassis. There was another Driver/Receiver and Normal Intensity character generator board (so I think that technically brings me up to 24 terminals I can attach) but there was also a variant of the DT board I already have (different part number and slightly different component arrangement) which may actually be very good, because we still have the unconfirmed report that the DT board is reworked when the system is upgraded to IV/90, so if this is an original IV/70 configured board, for testing purposes that would let me run with that whole expansion cabinet omitted.

11003104-52-fr_s.JPG


The big item however was the memory parity board.

11002712-A-fr_s.JPG

This is missing in my system but is required for the system to run, this means we are now just missing the two I/O interface boards that would sit next to this. Note the RAM 9 chips are remarked. They were originally P/N 91100091 but have been relabeled as P/N 91100101. No idea why. Perhaps these were tested with tighter margins and this deemed more suitable for parity control?

There is also another board that says its a synchronous communications adapter. I cannot cleanly tell if this was a single board or part of a multi board set like my other comm board.

11016431-A-fr_s.JPG


Board photos have been sent off to bitsavers for upload. I've added the chip part numbers to my running catalog. They will need to be recapped as they all contain those annoying 50uf 50v Sprague capacitors that seemingly are all either completely open or want to short soon after.
 
Last edited:
A terminal has been located.

I noticed another Four-Phase keyboard appeared on ebay (I know for a fact that I have saved searches and notifications setup and I am *not* getting notifications on these listings so I am guessing I'm missing out on scrap lot listings that are going up and almost instantly selling) and decided to inquire with the seller if they perhaps still had the terminal half. They did! It ended up costing me something like $200usd for the keyboard and terminal as-is and this is a VERY steep price but after two years of looking this is the first complete terminal I've seen for sale it was time to commit a bit more into making this work. The downside is it will have to take The Pony Express to make it from Wisconsin back to BC, so it may take a few weeks to a few months before it arrives. In the meantime, schematics for the keyboard, analog board + PSU and the digital board are already on bitsavers.
In the meantime as I've looked over the schematics I've realized that the terminal is mostly just composite video. The back of the IV/70 assumes one terminal per socket (and they are all Winchester plugs, so yay! money!) but you can if you want daisy chain up to four terminals, which uses interlaced video multiplexing. The keyboard needs Data_0, clock and sync but the video portion just needs VIDEO. Not even a balanced signal. Just analog video, accessible from up to 2000 feet away.
In theory, if you do not daisy chain terminals you do not need the CRT portion if the schematics read right because all the smarts in there are for demultiplexing and blanking the video signal when multiple terminals are in the chain. You just need the keyboard and you can make your pick of a video monitor with composite sync.
when the monitor arrives I'll be ready to take more photos, deal with its nasty cataract and do the other preventative maintenance. I have I/O boards dispatched on loan which if the planets align will get the system into a basic state. We're still a long way from saying it's alive but we are absolutely in a better place right now than we were at the beginning of the year. Hardware donations are still welcome btw.

While discussing disk packs for the system we are still running into issues confirming exactly what 8231 packs it wants. Diablo 30 drives came in various sector sizes, but many were hard-sectored. Looking at the filesystem arrangement in the Bitsavers book on peripheral programming it is alluded that it expects 8-sector packs. These in comparison to the 12 and 16 sector packs that DEC loved to use are nowhere near as common. If I ever do source an 8230 controller this still puts the disk drives on ice if a pack or multiple packs are unobtanium. It may become preferred instead to look into virtual disk emulation. I wonder how the RK05 emulator project has been going.....
 
Last edited:
Back
Top