• Please review our updated Terms and Rules here

Four-Phase Systems IV/90

While talking to the local Four-Phase guy about the issue of 2N3643's going pop he asked I go over the power supply again suspecting either one of the rails have gone out of tolerance or there's a considerable amount of ripple. I mentioned I had already checked this but he said to go through it again and more importantly, load and adjust the voltage rails to spec. I'll need to talk to him regarding if I should load and adjust each rail one at a time or load them all at once and adjust them. As you can see on the first page there are multiple adjustment pots underneath but on my first pass beyond making sure the rails were in tolerance I didn't dare touch them so he'll be helping me double check them next time I'm on the coast.

I also determined the replacement nylatch bits are available, however there's a large catalog of both pull pins and the part that remains captive in the part. A few pieces I found around here were the wrong sizes. I tried plastic captive panel screws for stuff like car dashes and found they were not sufficient.
Quotation also came back to make a replacement aluminum cover for the top. A single sheet with two bends and four screw holes is. $300.
I'll be looking for other sheet metal services....
Last edited:
Our local makerspace is relocating and I'm unexpectedly getting some of my infrastructure back. In that is a nice half rack so I can now put everything into a rack and stop shuffling the boxes around. IT should fit all the cabinets I already have, but a tape drive and a disk drive as well? Not sure.
While I was at VCF West I located some Winchester connectors and a pile of pins so I can make cables for the back of the NP80 to a Disk drive, however I forgot to grab some smaller connectors for the terminal mezz board (uniservo had them on his table for $1 each. Blah!) so that's still something on the list to do. It was alluded however that some series 30 drives might be available in the future but I need to verify if the controller in the NP80 was for a CDC or Diablo.
Speaking of DOS the flight to/from Midwest gave me time to look over the peripheral programming and DOS manuals. The obvious disk and tape commands are in there but I noticed there's an awful lot of fluff in there for card reading and punching. I was never aware that a card punch was available from any vendor. Certainly not Four-Phase. They say in the manual that the source for the driver is included so an end-user can DIY something should they want to output to cards.

I have also been told that there's an AL1 CPU and a parts board waiting for me on the coast this weekend. It's a loaner but that will allow me to get the main system up without the NP80 which is still a whole bag of bitslice mysteries.
Last edited:
A pair of IV 70 CPU boards have been delivered on loan to assist with the debugging process. The goal here is to get life out of the front panel, then we can resume trying to see if the IV/90 expansion can be salvaged.



There are two revisions I received with minor board-level alterations, both however are missing the AL 2 and AL3 chipsets, so I need to do a little research to try and figure out what those do, if they were in fact options. I do have a fairly primitive catalog already compiled of IC part numbers for Four-Phase's own chips but no datasheets as of yet. Even trying to assemble pinouts is a bit of a challenge entirely due to Four-Phase never intending to publicly release that information, so you end up deciphering them from schematics, or Lee's TI Vs. Everyone court demo summary.

Last edited:
The last of the Four-Phase photographs are done. Every corner of the IV/70 cabinet, the NP-80 and the IV/90 cabinets are now documented and organized. The front panel of the 70 was the last major pain because the wiring and keyswitch assembly have to be desoldered and flexed out of the way.


I updated my lists, replaced a few photos I took last year and sent them all off the Bitsavers for final processing. They'll be available at some point.
New connectors to rebuild the communications adapter are now on order. I also ordered connectors to rebuild the missing cabling for the DT-to-distribution board since mine were missing. The wiring diagrams are on bitsavers. I was considering also buying 86 pin sockets to make a extender board with a few extra lights for things like the voltage rails and bus test points but before I could get to that point we lost the 5v rail, plus I am not smart enough to design my own boards, even if it's just 86 traces from one end of the board to the other. :mad:
Well I was warned that this might become an issue so the power supply will need to be pulled.
Also by chance someone's office joke was on ebay. It was a full keyboard for a Four-Phase terminal, but spraypainted gold and labeled as retired in 1991. Kinda expensive to get it most of the way to my door, but I only have the inner assemblies and not the housing, so I went for it and I guess someone's gonna be exiting out of retirement after 30 years. LOL! Now just to find the rest of the terminal. While not entirely necessary as it's for the most part just an analog video display with the keyboard being a digital passthrough with its own wiring back to the computer it would at least be nice eventually to have a proper terminal for the system as the DOS executive does do a lot through it.
It is amazing how hard it is to make ebay Saved Searches behave. "Four-Phase Systems" also pulls up a lot of other crap, but the keyboard was listed as "four phase" which was missed in the search and came up on a manual check. Trying to add that to the search criteria overwhelms the results with unrelated crap.

Edited: I also gave up trying to source a small quantity of Nylatch pieces. Everyone wants you to pay up for kits. I have an alternate method I'll try tonight.
Last edited:
So the idea is that instead of using Nylatch to hold the console panel in place I used rubber cement to attach nuts to the backside of the mounting holes. On the other side I used a black annodized screw with a rubber washer as to not crack the panel and now doesn't look out of place or risk falling off and being broken. (again)



I'm getting a bit of pressure to stop messing with cosmetics and keep proceeding with this project to baseline the machine with front panel activity. Understandably so though, as the minimal testing is requiring loaned components.
You can still buy black thumbscrews, which might look better. You can even get them black nylon.
Just google "black nylon thumbscrew". Rather than gluing a nut to the backing panel, if it's metal, you could install rivnuts. Very secure.
Last edited:
My sourcing of parts locally have pushed me to this. Even to get a metal shop to bend a new lid nobody wanted to party, much less return my calls and quotation requests. Everyone else with a front counter wanted me to buy them per 100.
(I'm looking at you, Fastenal)
My sourcing of parts locally have pushed me to this. Even to get a metal shop to bend a new lid nobody wanted to party, much less return my calls and quotation requests. Everyone else with a front counter wanted me to buy them per 100.
(I'm looking at you, Fastenal)
Is the lid lightweight metal? Is it simple? Sometimes you can approach a HVAC installer to do simple work. Many have a shop with a shear and a brake. Bring a 12-pack of Molson to sweeten the incentive.
My own HVAC guy had a 4 foot shear and brake in his truck...
It's a sheet of aluminum, two bends, four holes and four recesses if you want to be fancy about the screws. Identical to the bottom cover, so you even get a template.
I don't know what the hell it is with this town but to get almost anything done I have to travel to the coast before I can find people willing to do one-off jobs and orders. Really frustrating and VERY time consuming.
My sourcing of parts locally have pushed me to this. Even to get a metal shop to bend a new lid nobody wanted to party, much less return my calls and quotation requests. Everyone else with a front counter wanted me to buy them per 100.
(I'm looking at you, Fastenal)
Same nonsense her in Perth in Western Australia.
All the local workshops are dreaming of the big recurring orders from the big mining companies and are not interested in little one-off jobs.
Either they quote ridiculously high thinking you are desperate enough to pay that much, or tell you outright they are not interested.
No wonder even smaller industrial customers find it cheaper, easier, quicker and better quality to get stuff made in China.
They're all tin workers and HVAC like Chuck suggested. The next step above that are commercial fabricators (stainless steel sinks, wash benches etc.) and above that are heavy industrial fabrication. I'm sure they'll do the job if you push them hard enough but beyond galvanized plenum steel they don't have the correct material and neither do I. I actually used to have the exact material Four-Phase used (1/16" aluminum sheet with a yellow staining) but it was lost when the local makerspace relocated and was presumably recycled.
It also doesn't help that I'm off work at 4pm and so is everyone else. Can't email them. Can't get anyone by phone and can't even walk in the door....

Bit of a stretch here but would anyone have a list of known good slot allocations? Still thinking about how we had parts overheating and popping when certain boards were in play and how the backplane while a passive bus does have custom wired slots. Up to now I've only gone on assumptions that boards are correctly inserted and that matches the labeling beside each slot. Looking at MITA's system (which does have different boards, just to make this fun) There ARE boards in places different from mine. I'm wondering if I'm running into the same issue the DEC people have when you drop a normal Unibus or Qbus card into a modified slot. I have reached out to him in the hopes he can send me a manifest of what board are arranged where in his systems, but beyond that I don't have any official word on how Four-Phase configured the boards.

Speaking of documentation, going through the stack of scanned documentation from Chicago has in the handbook a section regarding the operation of the NP80, running it's internal diagnostics and understanding its fault conditions. Reading through that it seems I'm getting parity errors from the memory, which isn't surprising as I have yet to touch the ram board and it has a lot of ram stuck in their sockets and they almost all have corrosion on their leads.
You may have to do some serious legwork to put things together--and pay for it. 24x36 metal sheet goods can be found pretty easily in thinner gauges, but 0.0625" thickness may require ordering from a specialty supplier, say Millennium Alloys in Kelowna. Nowadays, custom metal fab shops like working in ferrous because shaping and welding is easier that with nonferrous. You should also check out small aircraft repair shops--they do a lot of work in aluminum.
Oh I'm not hung up on the material and I'll gladly use a piece of steel if its available (aluminum sucks to bend). I just can't find anyone to do the work, period. :p
After realizing my card arrangement was wrong earlier this week I had time last night to generate a new slot list of my system compared to the one pictured at MITA and it's clear now there's major problems.

-The RAM boards are in the same locations. I still cannot confirm if these are 96K or 48K boards.
-The DT board is in the correct location
-MITA has only one CG board with unknown intensity control, so that machine can do 8 terminals rather than 16, which is fine
-There's a mystery board I cannot identify in the "MP" slot and whose visible component layout does not match any of the schematics
-We both have the IV/90 CPU extender in the same slot. His front panel lists the IV/90M, so I can't question its location
-There appears to be two boards for the I/O Interface (marked I/O INT 1 and 2 on the chassis) that connect a lot of wiring to the terminal distribution board and mine are both missing. I can make cabling for them but looking at how the AL1 processor board interfaces in the schematics it looks to really want these boards.
-The Driver/Receiver board is in a different slot (Remember how this was popping parts on the DT board whenever it was installed? This is probably why)
-The tape interface seems to be in the same location
-There's a line printer card in one of the last slots and another card I cannot identify as its layout is also not in the schematics.

I've reached out in the hopes I can get a better idea of what cards and their part numbers are installed but if the I/O interface subsystem is entirely missing that's a pretty major problem because either it means the I/O bus or the terminal subsystem is electronically isolated from the CPU or worse, the glue to make the system work at all is missing. IF we are very lucky I can still bring the system up with a front panel and only a front panel but that's it.
Last edited: