Base Junior computer, quite a small system: PCB 80089-1,-2,-3.
Equivalent to a KIM-1 without serial TTY and cassette interface: keypad, 6 seven segment LEDs, 1K ROM (2708), 1k RAM (2x 2114). Partial memory decode as in the KIM-1: first 8K block mirrored in memory.
Subtle differences in the ROM and hardware (RIOT 6532 versus RRIOT 6530: I/O and RAM at $1Axx instead of $17xx).
The monitor in ROM is quite similar and inspired by the KIM-1 monitor, but not identical.

Circuit diagram
PCB front

(from Book 2, in Micro Ade format

	Junior Computer first article
	Hex dump of Junior Computer Monitor ROM ESS503
	Listing of Junior Computer Monitor ROM ESS503
	Junior Computer Monitor ROM ESS503 Original, identical to ROM dump in article and book, for $1C00
	Source and listing of Junior Computer Monitor ROM ESS503 In TASM format
	Junior Computer Monitor ROM ESS503 assembled for $FC00, better for expanded fully decoded system.
	Source and listing of Junior Computer Monitor ROM ESS503 For $FC00, in TASM format
	Junior Computer Monitor ROM ESS503 assembled for $1C00, in a 2K (2716) ROM image.

Have a look at the Elektor Articles and Books page for a mullti-lingual overview of all publications on Elektor/Elektuur Junior and more.

PCB back

PCB layout front (from March 1980 Elektuur article)
Note that this layout is not as shipped, the Junior PCB’s were front/back swapped. The book is correct.

PCB layout front (from Junior Book 1, as shipped)

PCB layout back (from March 1980 Elektuur article)

PCB layout back (from Junior Book 1, as shipped)

LED display PCB and layout


Address sticker


Photo of (stripped clean) PCB front

Photo of (stripped clean) PCB back