Adding EPROM sockets to your Juno-106

What’s the deal?

Later Juno-106 models have masked ROM inside the CPUs instead of
external EPROMs. The PCBs however are the same, so there is an
empty spot on the PCB for the EPROM and a jumper to select
which memory to use (External=EPROM or Internal=CPU masked ROM).
On the module (voice) board there is also a 40H373 circuit missing so
you’ll need to add that one as well.

CPU Board

See picture below.
1. Remove (cut and discard) the resistor at jumper position (I) (Internal) (1)
2. Add a jumper wire at jumper position (E) (External) (2)
3. Add a 28-pin socket for EPROM (3)


My modded CPU board with added EPROM socket and jumpers changed.
I also replaced the battery and fitted a battery holder.


Module (voice) Board

See picture below.
1. Remove (cut and discard) the resistor at jumper position (I) (Internal).
Add a jumper wire at jumper position (E) (External) (1)
3. Add a 28-pin socket for EPROM (2)
4. Add a 40H373 IC (3)


My modified module board with EPROM fitted, jumpers changed and 40H373 mounted