Customized Aces Index > Droy Trastero's Jupiter Ace

Droy Trastero's Jupiter Ace

"The information in this page has been translated from Droy Trastero's web site. Droy also gave the Jupiter Ace archive team permission to use his images and information. I do not speak Spanish so I'm sorry it some thing has not been translated correctly - SPT"

ome 15 ago years Droy bought a electronics magazine in Spain called 'Revista Spanish of Electronics'. In one section dedicated to the micro computing, frequently published articles and programs, etc; for ZX81, ZX Spectrum, Vic20 and Jupiter Ace. In spite of the fact that I was happy with my ZX-Spectrum. I found the Jupiter Ace began to fascinate me, then when I found on the internet its schematic I could not resist the temptation to build one. I had already had tried to obtain an original machine but the small number of units sold worldwide the Jupiter Ace had got the attention home-computer collectors. It is rare that one appears in auctions on the internet and can reach incredible prices. The the last one that saw sold for 80.000 Ptas. At these prices getting hold of a original Jupiter Ace for my modest collection was going to be difficult.
But, like the ZX80 computer (predecessor of the ZX81) all the components of Jupiter Ace are very common and you kind find all the parts in electronics stores. This was probably due to Jupiter Cantab being a small business and did not have the funds to design and manufacture custom made chips like the ULA's made by Sinclair Research for the ZX81 and later for the ZX Spectrum. Jupiter Cantab used off the shelf ordinary components.
Well, those are some of my motives to build one, but its the challenge to build a home computer from zero modifying some things from the original design, also to study how it the computer works.

The Original plan and the modified one.

As I mentioned before all the components of Jupiter Ace can be found at electronics stores. I have made some changes to the original schematic. I was able to lower the cost and to simplify the design and also to not waste the time looking for component that are common, but were already being to be difficult to find.
In the original schematic drawings I used were done by Bodo Wenzel who has re-drawn he schematics copying partly the original schematic drawing, and by taking notes from real Jupiter Ace. In the download links you can study both the modified schematic and the one made by Bodo. Both schematics work, but I recommend my one which is simpler to build in practice.
I have replaced 2114 RAM memory chips (1024x4bits) with RAM 6116's (2048x8Bits), we wasted a Kilobyte in each one by taking the A10 pin GND, but 2114 are hard to find, but cheap and simplifies the wiring. The 6116 have independent lines for /OE /WE and /CE, whereas in the 2114 with /CS it controls the activation of the chip and /WE controls the reading or writing. By that I have had to add another chip a hex inverter (Z30-7404) to control the /OE in the Video memory (Z5-6) and character font RAM (Z7-8), and to connect line /OE of the main memory (Z3-4) to line /RD of the processor.

The Jupiter Ace has an 8 Kbytes of Forth in ROM, as two 2532 EPROMS each holding 4 Kbytes of data. I have replaced these with one EPROM of 8K (2764), this simplifies the wiring for me. My Eprom programmer did not support the original type of eproms used by Jupiter Cantab, also I had some 2764 eproms extracted from old pcb.
I have chosen to construct the project on a strip board. In my opinion this is simpler and it requires less "technology" than the method of construction than a printed circuit board. After visiting my page Sergio Gimenez, a great fan of electronics and computers decided to design the printed circuit board, you can see his PCB version of a Jupiter Ace here.

What you need to construct my Jupiter Ace?

First start a print out of my modified schematic of Jupiter Ace, if possible print it to the A3 size. As you start to build the Ace you can mark with a fine pencil or pen in red each connection as I did, this way you will keep track of where you are in the construction. Here is a list of the components used:

ICs - In the list you will see numbered ICs with two numbers (Z1-2 Eprom), this is because this component replaces two in the original design (in the example Z1 and Z2).
Z0 Z80A CPU or the clone NEC D780C
Z1 2764 (EPROM: see ROM)
Z3,5,7 6116 (x3)
Z9-11 74LS393 (x3)
Z14-18 74LS367 (x5)
Z19 74LS00
Z20 74LS08
Z21-22 74LS11 (x2)
Z23 74LS86
Z24-25 74LS02 (x2)
Z26 74LS32
Z27 74LS74
Z28 74LS166
Z29 74LS138
Z30 74LS04
U1 LM7805
Q1 2N3904
Q2 2N2369
Q3 BC183
D1-11 1N4148
R1 4K7
R2 47K
R5 12K
R3-4 R6-7 1K
R8 270
R9 22K
R10 10K
R11-23 1K
R24 10K
R25 220K
R26 330
RN1-2 8X1K
C1 30pF (x2)
C2 100 pF
C3 2,5uF
C4-5 47pF (x2)
C6 47nF
C7,11,12 1uF (x3)
C8 2.2nF
C9 100uF
C10 100nF
C13-21 100nF (x10)
13 IC Socket 14 pins
 7 IC Socket 16 pins
 3 IC Socket 24 pins
 1 IC Socket 28 pins
 1 IC Socket 40 pins
 1 loudspeaker 8 Ohms
 1 piece of strip board. [see note *]
 1 Modulator UHF UM 1233 [see note **]
 1 set of male pins.
 1 strip of female pins
 1 crystal 6.5Mhz (or 6.5536 Mhz which is more common)
solder (preferable thickness 1mm)
cable - single core 0.6mm is what I used
Soldering iron 30 Watts
Hobby Drill
Drill bit 6mm multi meter
and lots of Patients
(*) The veroboard or strip board can be of any size you like as long as the components fit and that you leave at least two connection holes free for the interconnections between ICs.

(**) modulator can be very difficult to find, if your television has Euro-connector (SCART) you may not need it, because you can directly connect the video signal to the pin 20 that corresponds to "composite video input", and the 0V/GND to the pin 17 "GND Video".

Euro-connector (SCART) Pin outs.
If you do not know much about electronics, Some advice.

This project is not really for a beginner but if you have patience's, and some skill with a soldering iron you will have fewer problems

Some components can be difficult to track down depending on where you live, obtain everything before you begin, specially the Z-80A cpu and the EPROM. Remember that the EPROM contains the OS of the Ace, the Forth system. You will need to have an EPROM burner to record the Forth OS on to the EPROM or get someone to do it for you. The OS file in the download section. In some electronic stores they have a EPROM burning service for a few Euros. If the modulator is difficult to find, although nonessential, read the note in the parts list for the SCART video connection.

The thickness of the cable is very important to conserve the visibility of the area in which you are working in. That said, be careful with single core wires when solder though the veroboard holes to avoid short circuits on the underside. Soldered wire ends can be trimmed with pliers soon after you have made the joint to avoid shorts later. I prefer to work with mu own pcb, but this is a special case due to the complexity of the schematic. It's might take three times as long designing a pcb than doing a veroboard version. I have used a 6mm drill bit to remove parts of the veroboard, by slightly drilling by hand the holes which will remove part of the veroboard track, instead of cutting the track with a blade, you possible waste more of the veroboard, but is worth while in the end saving you lots of trouble.


Also have left five holes between IC pins, So after cutting the middle column to separate the connection. I have left two holes on each side for side connections. This may seem a waste but when you try to solder a wire in the hole that's already occupied by another remember this advise. If you organize the placements of your IC's and parts with two holes will be sufficient.

How I started

In my opinion it is very important to follow an order not to duplicate and to complicate the work, this how I did it.

Preparation of the Veroboard.

First, think about where to place your components on the veroboard, as I have said before I left five holes between the IC pins. So when I cut away part of the copper track it leaves me with two holes on each side of the IC which will make the soldering of the cables easer. The positioning of components will depends on the size of your veroboard you have. The space between the ICs will soon be take up with wires connecting the ICs together. In the photo you can see the socket of the CPU on the left , next the EPROM. The 6116 RAM sockets are the blue ones. The two pin strips at the bottom of the EPROM socket are the keyboard connectors.

Once you are sure that your components are in the correct place, mark with a labeller the track pieces to eliminate. Use a 6mm drill, lightly drill the track to cut away the copper to make a break in the track where you have marked. Do not drill to deep, just take away the copper.

Check that the cuts are good breaks, and that the edges of the copper tracks do not make shorts with adjacent tracks. Take your time make sure the track cut clean and clear with no shorts before you start the next task.

Positioning of the sockets and other components

Sockets and other components in place, I have reserved the near side track for the 5V power rail and the furthest one for the GND, 0V. From any point on the veroboard a wire from these power tracks can feed the ICs. Its better carefully plan and to mount the components before beginning with cables. In the photo you can see the veroboard in first stage of construction.

Soldering in the cables

The best way to start is with the data lines (D0 -D7) Beginning at the processor and to take it through all its route before beginning with the address lines and later the rest. The order is important not to lose the control of which ones you are soldering in place. Making a note on a printout of the schematic coloured pencil the connection that you have made will help you to keep track of which wire you have soldered in place.

Below are a few images of the veroboard build.


Take a look at the schematic to follow this example:

D0 is pin 14 in the Z80A, the soldered wire connects to pin 10 of the EPROM (2764), now you can solder in the other hole available a wire to complete the connection to pin 9 of RAM memory 6116 (Z3-4), you can now connect the other hole available in this last pin with the R16 resistor the same until you finish completely with D0.

Explanations to the schematics

This is typical in digital schematics the IC power pins of the ICs are different to one another check the following:

IC's with 14 pins have there pin 14 connects to the +5v and pin 7 to 0v (GND)
IC's with 16 pins have there pin 16 connects to the +5v and pin 8 to 0v (GND)
Z80A pin 11 should be connected to the +5v and pin 29 to 0v (GND)
In 2764 memory EPROM pin 28 to the +5V and pin 14 to 0v (GND)
In RAM 6116 IC's pin 24 to +5V and pin 12 to 0v (GND)

The number system in the ICs legs are all the same. Pin 1 is to the left of the notch in the chip and the leg count goes down and around so the last pin is the right leg next to the notch.

The Modulator UM1233 has three connections, one is the case that is 0v (GND) and you must connect it to the 0v (GND) of the circuit. The other two are the 5v and the video connection. The modulators video signal is connected to the pin 1 of JP3 as you can see in the schematic. To tell which of these two modulator connections is the video signal should be soldered to see the image below. It is very important to connect a capacitor of 100uF between power and 0v of the modulator to avoid the electrical noise produced by the digital circuits which might interfere with the TV image.

You may ask why are there so many 100nf capacitors all in parallel. These capacitors are for filtering electrical noise from the digital circuits. You must distribute them strategically so that every IC has one across its power lines . You can add so many as you want, will not do any damage to the to the circuit. You can see the capacitors in the veroboard because they are underneath directly soldered to the legs of the ICs across the 5v and 0v lines.

In the last image you may have noticed seeing an empty socket next to the modulator. This was left in place to make some changes to the video circuit, I did not in the end as it was not necessary.
The Keyboard

In the schematic you can see one connector for the keyboard keys. I have used strips of header pins to use as the connector to a keyboard. I used the keys of an old PC keyboard by making a simple pcb and soldering in the PC keyboard switches. see the images below.

Taking a part the PC keyboard    Making the pcb for the Ace's Keyboard

Taking a part the PC keyboard and Making the pcb for the Ace's Keyboard

Adding the PC key switches    Underside of the keyboard pcb all keys solder in place

Adding the PC key switches and Underside of the keyboard pcb all keys solder in place

Ready to add the key caps with the legends    Notice the bent header pins for connection the Ace.

Ready to add the key caps with the legends and ready to test.

All done ready to test.

Nice job done there!

 Ace and Keyboard together.

Ace and Keyboard together.
The box

Here you can let you imagination go wild! I personally like the meth-acrylate things, so I took copy of the of a veroboard, I asked a friend who uses this meth-acrylate material all the time to build a case for me. As you can see in the images.

In case of problems

When you power up for the first time after tuning the television set you must see a black screen with a small cursor in the left inferior corner, if you press a enter it will respond with a "OK" on the screen. Enter the command "VLIST" which will list to the screen all the Ace's Forth words in its ROM as in the photo above.

If you do not see the small white cursor in the left corner. There could be that you have a problem. The best thing you cab do is to remove all the IC's from there sockets and verify the connection. Also check for shorts between wires.


All the necessary files for the construction of this legendary computer are here;-
Schematic for the Jupiter original Ace. - jupiter_org.pdf

Schematic of the Jupiter Ace modified by me to simplify its construction - jupiter_modif.pdf

Jupiter Ace ROMs for the EPROM

Thanks to:
To Bodo for Wenzel for sharing his information about the Jupiter Ace. He answer all my questions kindly and help me to out when I was trying to understand how the video circuit works.
Juan Miguel Z. for the loan of his tools!
and my Parents


Lo siento, no se como titular esto en Español, pero ya sabéis lo que quiero decir. Yo comparto esta información, y la contenida en el resto de ficheros sin garantía ninguna y por supuesto sin responsabilidad de los daños que pueda causar su uso indebido o inadecuado. Lo que te puedo decir es que todo funciona perfectamente y nunca se me ha estropeado nada en los experimentos, pero... tú mismo.

New features and Changes

January 2003
Found an error in the published schematic, pin 2 of the memory Eprom Z1-2 must go connected to A12 and not to GND.

April 2003
Sergio Gimenez found an error in the circuit of control of cassette, pin 2 of Z29 must go to D3 and not to D0, and 2.5 C3 must be of uF. Also it show us with the design as a printed circuit of our version of Jupiter. thanks Sergio.

May 2003
Héctor Romojaro told me about several errors in the list of components in the page and in the numeration of some of them (repeated, not R20 dand nothing of RN1 and RN2 etc). Héctor Thanks.