My Home Built GRUNDY NEWBRAIN

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As already mentioned on the history page, I purchased all the component parts of a working Newbrain A, from the original Greenweld Company, then based in the outskirts of Southampton. These included a mainboard, a scandanavian keyboard and a RAM board with all its components non soldered. The photos below illustrate how I turned them in to a working unit.


Newbrain Mainboard


The two labelled ROMsThe complete, and from the production stickers on the top left corner, tested and fully working, main board. This is a very early, version 1 board, with totally EPROM (x2 2764) based operating system and character set (2732), ROMS. It was made possible to switch to mask programmed ROMs using the wired jumper positions in the top right hand corner. I have seen later versions with mixed EPROM and ROM, as well as larger, single 128K ROMs, rather than the two 64K, which may be made possible by a simple link on the board, switching between 5v and A13. To connect the RAM and keybord, not having the original connectors, I attached a Single In Line, short socket to the bottom right ribbon cable position and two rows of SIL pins into the ribbon cable positions for the RAM on the bottom right. You can also see the short length of aluminium I attached to the power transistors used for voltage regulation, to soak up the heat created, as well as the two small electrolytic capacitors I had to move in the far right, bottom corner, as the fouled the RAM card when attached!


My Newbrain Keyboard


The scandanavian (?Norwegian) keyboard, came complete with attached ribbon cable, as can be seen to the left. To this I soldered a small piece of vero board, with a row of SIL pins, to attach to the matching socket on the main board. The date visible on the back of the PCB, visible below, is July 1983, which may be a design, rather than manufacture date. Note also in this view, the very different PCB layout, lacking the long line of connections for the display unit, as opposed to the AD model shown on the next page. The keyboard has been little used and subsequently I have used it as a source of key caps. Hence the missing SHIFT key top on the left and the highly worn New Line top, on the right.


Back of keyboard


RAM Board


The RAM board above, had most of it's components present, with the components held in place by having the lead ends knibbled over. However, not all the components were there, the more expensive SIL resistor sets in particular. I only bought one, which is visible as the red component, in the underside view shown below. Thanks to having the circuit diagrams, I was able to identify the value of the missing components. I had available enough individual resistors to replace the SIL components, and use two tantalum bead, (light blue), capacitors in place of the specified electolytics. Note also the two rows of red, SIL sockets, and the predominantly blue sockets into which the RAM chips are placed.


Back of RAM board


Front of complete Newbrain

The assembled Newbrain. The main board and key board are bolted together, with two nuts forming the separator, together with the sheet of corrugated cardboard, rather than the paxoline used in the production machines. The extra thickness produced by using sockets for the RAM, together with the SIL connectors, rather than ribbon cable, probably make the asssembly too thick to go in a Newbrain plastic case. It is thus just as well that I decided to mend my broken purchase.

Back of complete Newbrain


The top, right hand edge of the main board, showing the vero board strip I used to connect to the keyboard ribbon cable. Note also the larger, socketed chip, a COP420, which is a dedicated microcontroller used for keyboard scanning and other I/O facilities.