This machine is not easy to manoeuvre; it takes two people to lift it. And this is with a switch mode power supply.
The screen looked to have deteriorated. There were what looks like mould spots all over it. I thought that the CRT may have been broken, but casting light on it showed the spots were not on the phosphorous but just below the surface of the glass.
It looked like it may have been under a protective layer. A check on the web confirmed that this is a case of CRT cataracts where the adhesive holding protection screen on deteriorates. It’s not terminal; it can be repaired.
The owner showed me how to take the top cover off – just two screws at the sides that need to be loosened.
Inside there is a long baseboard with a terminal block at one end and a passive backplane at the other. It was not clear to me whether each of the 7 cards had to be in a particular location.
The primary power supply is located on the right and the secondary low voltage supply, providing regulation of various voltages, is on the left.
The backplane did not appear to correspond to any bus that i had seen or read about.
The CRT is at the front left and is driven by the board at the far left of the card cage. The drives are mounted in a frame at the right.
The primary supply is a switching unit. It provides several unregulated outputs to the secondary power supply to create all the required voltages for the backplane and the drives. I could not see any of the infamous Rifa line filter capacitors. All other caps looked fine.
The floppy drives were removed, cleaned, lubricated and refitted. The thumb screws up the top retain the drives.
The main processor is an 8085. The card doesn’t have a lot on it but includes the printer interface, the keyboard interface, and the boot ROM. I don’t have any schematics or technical documents, so exactly how this card works is a bit of a mystery.
The date codes include 1981 so i’m thinking this was quite a late unit. There seems to be a lot of kynar for a design that i’d expect to be a few years old.
The DRAM card provides 96kB of memory so it must have some form of windowing going on. It uses 16kb DRAM chips which worried me a bit because they are often unreliable.
There are two floppy disk controller cards, which is unusual; normally a controller card would look after multiple drives. This was either very inefficient, or there was some scheme that allowed concurrent reads and writes.
There is a switch on each board near the 34 pin connector that sets the controller for Drive 0 or Drive 1.
There’s a character ROM at the top of Video Card 2. Character memory on the right of it: 6x256x4bit SRAM. That doesn’t seem like enough for a 24 x 80 display, so something else must be going on.
The only I/O that i could see was the printer port. No serial port is sad.
Both the printer and the computer have 110V rating plates but the seller assured me that they had always run both units from 240V and the accompanying power leads certainly supported that proposition.
I thought that the supplies had almost certainly been converted, but I didn’t want to leave it to chance. I checked each unit and went looking for some evidence of the conversions. There is a wire on the power supply which has been moved from 100V to 200V.
The keyboard is secured by two screws underneath the unit, and the board is screwed to the surround. It uses a D8748 microcontroller.
All up, the machine struck me as being in pretty good shape. Sure, it’s just a word processor, but underneath it’s a computer looking for an operating system.