Hardware articles index > Build Your own Ace

How to build your own !
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

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