The Junior Computer hardware and software is described in detail in the books and articles, see there for details.
Base Junior computer, quite a small system!
PCB layout front
PCB layout back
LED display PCB and layout
Photo of (stripped clean) PCB front
Photo of (stripped clean) PCB back
Interface card, adds more memory, cassette interface, TTY interface
Circuit diagram part 1, ROM, RAM, VIA
Circuit diagram part 2, TTY interface, audio cassette interface
Interface card PCB front (note not on scale!)
Interface card PCB back (note not on scale!)
Interface card layout
Backplane PCB, part of it could be used to connect Junior PCB to Interface card.
Musicprint kit and cassette interface
The Junior was sold as a kit by the firm Musicprint, read here the extra instructions in the kit.
It took Elektuur some time to add a cassette interface tot the Junior design, a year until the Interface PCB appeared. Many users therefore bought the socalled musicprint cassette interface. See here the description and circuit design.
A 2732 EPROM can be used instead of the 2708 EPROM when you perform the following:
– cut the traces +12 and -5V
– K6 to the VIA,
– K7 to the EPROM.but leave K7 to the 7401 intact for the STEP function.
– /CS from VIA to K3 to move the VIA to page 0E (jumps in the EPROM are adapted for that)
– /OE from the 2732 to ground
– A10 and A11 of the 2732 to the addressbus
– /CS from the 2732 via an inverter to A12 , note that there are two unused ports in the 7402 with grounded inputs,: cut those! and add a pull up resistor