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CN Customized Ace


This Ace came from Rayleygh, Essex, UK, and was customized by CN. Its become known as the 'IBM Ace', because the owner worked for IBM before retiring in 2005.

Its an interesting Ace as it came with a 16K RAMpack that was made from old IBM Memory Typewriter (hence a lot of removed parts and some of the board cut off) it is basically just 16K of Low Power Static Ram (8 Chips of 2K each) with addressing wired to suit the Ace (mapped as per a ZX81 16K RAM Pack). Some circuitry which was part of the original board will provide battery back up. It was built specifically for the Ace and is still in working order.

This Ace also has a full size IBM type keyboard. An extra 74LS245 chip which buffers the keyboard key presses has been added in line to the keyboard matrix diodes D1 - D8. The keyboard address lines and data lines are patch on the bottom of the pcb to a ribbon connector which attaches to the keyboard. Also, Note that the keyboard 'pullup' resistors, R41 - R45, 10K are in place.

Video output was provided with a small veroboard which seems to have been built for a specific monitor. There was no modulator in place which makes me think that this Ace was bought from Boldfield computing as a part-built Ace. Also, no speaker was present on the board, but two wires connect form the where the speaker would have been solder on the pcb and are soldered in place on two of the unused edge connector pads, solder side, (bottom). Another small modification is a reset line from the Z80A to another unused edge connector pad this time component side (top). When shorting this line with a GND it causes the Aces ROM to start running from location 0, performing a cold reset. CN also, made a large heatsink for this Ace which is made from a thick aluminum and twice as large. One other thing I spotted, was that the 2114 RAM chips are an early type.
The Keyboard
The full size keyboard.




CN Ace Note: the monitor board output mod
The IBM Ace pcb




Close-up of the video out board
Close-up of the video out



Close-up extra added 74LS245 chip



This is where the ribbon connector attaches to the keyboard.
You can also see the speaker connections to the used edge connector pads.


Here you can see the /RESET line from the Z80A solder to the unused pad
Also the keyboard 'pull-up' resistors in brown.



The Keyboard is from 'Key Tronic Corp'


On underside you can see where CN rewired the keyboard by cutting tracks and
soldering in new wires.


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