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How to build your own Jupiter ACE

by Grant Searle BSc.


This is the second of my "build your own" series of pages devoted to old micros which can still be built since they don't use custom components.

For many years now I have been working with the latest technology using high-powered computers. However, nothing nowadays can replace the time when the first home microcomputers hit the streets. I am a keen collector of the home computer era. Follow this link to see my current collection. In those days you HAD to make your programs fit the hardware and memory available. This added to the enjoyment of programming to see something you had written to fit in a few K spring to life.

The Jupiter Ace has a relatively straightforward design which makes debugging any hardware faults straightforward. If consists of the following modules:
The timing for ALL parts of the circuit
The CPU/ROM/RAM area
The display area

I must point out this is not a job for the absolute beginner. You will need to blow your own EPROM image and it will probably be a distinct advantage to have access to an oscilloscope in case it doesn't work. I can assure you the circuit supplied here DOES work without any modifications.

I have, however made the following modifications for my own version:

1. I used a 6264 SRAM to make the program memory 5K instead of 1K. The other 3K is not wasted - it is also available within the memory map.
2. The original Jupiter Ace used two 4K ROMS. I have used a single 8K ROM.
3. The Ace uses two 2114s for the display RAM and two 2114s for the character RAM. I actually had a large amount of 8K x 8 RAMs in my spares box so, although wasteful, works out cheaper and construction is slightly easier. The 6116 2K x 8 RAM chips are also suitable alternatives. Tie any unused address lines to one of the supply rails.

The complete computer is built on two pieces of perforated stripboard - one to hold the keyboard and one to hold the rest of the computer. All digital connections are made using wire-wrap wire as this is a lot thinner than conventional hook-up wire so the data and address bundles can be tied to form a neat layout. The positioning of the ICs in relation to each other matches the positioning in the original Ace.

I recommend printing the circuit out on an A3 sheets if possible. The scan is not perfect but hopefully you should be able to work out any areas which aren't very clear.

Begin construction by positioning the IC sockets (see my pictures below for guidance). Next I recommend wiring the data and address buses for the top half of the circuit. As each wire is soldered it, mark it off on the circuit diagram. This helps avoid any errors resulting from missing connections. Wire in the logic ICs, resistors, capacitors and diodes. As virtually all pins on every IC are to be connected, any errors made will become obvious as more connections are made. For initial testing, there is no need to wire the keyboard into the circuit.

Once all components are soldered and without any ICs inserted into the sockets, connect a continuity tester between the power supply pins. If a short exists then check the underside of the board for any missing track breaks or flakes of copper between tracks. If all is well connect a power supply (current regulated to 500mA if possible). Check the +5V and 0V connections on each IC socket. Turn off the supply and insert the ICs. Turn on the power supply and the television or monitor. If the circuit is working then expect a power consumption of around 280mA. A working circuit should show an small white square in the bottom left of the screen. If all is well then wire in the keyboard if not already done.

Parts List

No         Component  Type
Z0 Z80 (cpu) Z1,Z2 2732 (4K x 8 eprom) I actually used 2764s in my design as I had some in my spares box Z3-Z4 2114 (1K x 4 sram) I recommend using one 6264 to allow 5K RAM Z5-Z6 2114 (1K x 4 sram) I recommend using one cheaper 6116 (2k x 8) Z7-Z8 2114 (1K x 4 sram) I recommend using one cheaper 6116 (2k x 8) Z9-Z11 74LS393 Z14-17 74LS367 Z19 74LS00 Z20 74LS08 Z21,22 74LS11 Z23 74LS86 Z24,25 74LS02 Z26 74LS32 Z27 74LS74 Z28 74LS166 Z29 74LS138 U27 7805 (+5V reg) X1 6.5 MHz xtal Q1 2N2369 Q2 2N3904 D1-11 1N4148 C1 39p ceramic C2 100p ceramic C3 47n C4 47p ceramic C5 - C6 47n C7 1u tantalum C8 2n2 C9 100u electrolytic C10 100n C11,12 1u tantalum C13-21 100n R1 4k7 R2 47k R3 1k5 R4 1k5 R5 12k R6 1k R7 1k8 R8 270 R9 220 R10 10k R11-23 1k R24 10k R25 220k R26 330 RN1,2 1k x 8 L1 RF choke LS1 220r speaker My design used a speaker salvaged from an old Spectrum board! S1-40 SPST switch (keyboard) JP1 3.5mm socket (audio out) JP2 3.5mm socket (power in) JP3 RCA phono (video out) JP4 3.5mm socket (audio in)
Circuit Diagram
click here to down load.

Rom Image
Can be found here

Keyboard caps
The overlay here is sized to fit into the tops of a standard-size keyboard You can either resize as necessary.

Click here to get the keyboard overlay in Visio 3.0 format
Pictures of my finished version

Front of PCB

Back of PCB



Peter Liebert-Adelt - I couldn't have made it without the extensive information sent to me - thanks!

The team here at Jupiter-ace.co.uk, [Steve & Edwin] would also like to thank Grant for letting us mirror his site here. - thanks