The design of the Elektor Junior is well documented in the Elektor articles, books and other articles like the KIM Kenner. In many languages, the archive here is as complete as possible, but you could see some pieces of information in only one language section. The hardware components for the most part are not exotic, especially for the time of publication.
The software in the form of (sources of) the ROMs and applications such as Microsoft Basic and even Operating systems like OS65DV3 is also easy to find.

So with all this information available it is no surprise to see modern versions of the Junior. Some try to stay as close to the original design, others just take the ideas and implement it in a more modern an d convenient way.

Some obstacles in building a Junior are:

• the original PCB’s are only available as low quality magazine articles quality. And even then be careful, the original article mixed up front an back!
• the EPROM for the Junior monitor is a 2708 UV EPROM. A very old hard to get part, hard to program and requiring power supplies like -5V and +12V besides to usual +5V.
• the expansion card used a 82S33 PROM for the address decoding. Also an obsolete part and hard to program.

What designers can do:

• design the PCB’s again. Kicad e.g.
• replace the 2708 with an EPROM like the 2716 or bigger or an EEPROM like the 28C16 or bigger
• use a GAL or discrete logic for the 82S33 on the expansion board
• use a modern SRAM IC and increase RAM memory a lot
• modify the address decoding to fit the modern ROM and RAM
• obtain parts like the 6502, 6532 and 6522
• replace the hard to get 1 MHz crystal with a can oscillator
• simplify the power to +5V

Here are some examples of builds:

• Junior by Philippe Roca
• Junior Computer Replica by laurent-fr
• Junior PCBs by Werner Beukes
• Junior revival Bram Prosman
• Philippe Roehr on KB9 and OS65DV3.3
• Junior Computer ][

With thanks to Philippe Roehr from France I present on this page how he got KIM Basic 9 and Ohio Scientific OS65D to work on the Junior

Junior build

Philippe has build a Junior system with at least a main board, an expansion board, 16K Dynamic RAM board expanded to 64K and a floppy controller.

It started with the Junior itself, followed by the expansion card, The monitor software PM and TM were tested.

Floppy controller, RAM card behind.

Junior KB9 Basic

Philippe started with the KB9 binary from the KIM-1 pages.
Philippe then applied the process outlined in the Elektor articles to adjust Basic to the Junior character I/O routines and also improved the speed by adjusting the now unnecessary code that took care of the ROR bug in early 6502’s.

Philippe transferred the binary to the Junior with Ed’s utility KIMTape, producing a KIM-1 audio wave file. The Junior accepts this format, a bit slow but only needed once. After seeing all was well, Philippe wrote the now optimized Junior KB9 Basic to audio wave file, and made a hex dump on the terminal. I picked up the dump, a captured text file form a a terminal emulator, and wrote a conversion program to produce a binary.

All the files here: archive with audio wave file, dump on terminal, binary and conversion software.

OS65DV3.3

After building the Junior, having PM and TM monitor working well, KB9 Basic operational, the next step Philippe took was getting the operating OS65Dv3.3 operational.
He took the steps described by Elektor in the articles with some modern additions.

A Junior able to run OS65DV3.3 needs an expansion card,  a RAM card (his is 64K) and the Elektor floppy controller, which is identical to the OSI one (6850 + 6820 ICs)

Instead of a real floppy drive Philip used the hardware Gotek floppy emulator with the Flashfloppy firmware. And used the manuals images of http://osiweb.org, and the OSIHFE utility described in the OSI Web forum posts.

Elektor made a bootstrap eprom (ESS515 download here, source in Paperware 2) able to
* load OS65D (V3.1 or 3.3 as far as I know) from floppy
* give basic I/O capability (RS232 and floppy)
* manage hex display and keyboard
* modify OS65 for the hex display after the very first load to fully adapt them to the system ( about 10 bytes to modify)

Here the OS65DV3.3 disk image in native and Flashfloppy format ready to use.

During the second part of december 2020 Philippe added a real floppy controller and added the Ascii Video Terminal (new version of hackaday). With improved moter control of the floppy drive!

VDU board with OS65D

PMV for OS65D source checked by Philippe Roehr
PMV for OS65D ROM