Hardware · Kompakt 128k Modification
Memory expansion for Didaktik Kompakt by MDV. This is heavy modification, so it is recommended only for people with skills. There are 3 modes, selected by switch: USR0 128k mode+MDOS, 48k LOCK+MDOS, 128K mode witout MDOS.
How to:
- remove IC8 (GAL) and IC3 (EPROM) from PCB, solder sockets instead
- remove IC14 (74LS74), cut pin 1 from VCC, solder socket instead, put IC14 to socket
- separate AR6 from PLA with 470R resistor
- separate AR7 from PLA with 470R resistor
- cut original /CAS to original DRAMs
- with /CAS pin bent, piggyback new DRAMs to original DRAMs
- burn new JED to IC8, new EPROM and new GAL
- bend pins 15 and 19, put IC8 to its socket
- bend pins 18, 21, and 24 on SRAM
- bend pins 1 and 27 on EPROM
- piggyback SRAM to EPROM, bottom aligned, SRAM GND to EPROM GND
- add 100n capacitor between power pins of EPROM
- put this combo to IC3 socket
- connect SRAM pin 24 to EPROM pin 28
- connect SRAM pin 18 to IC8 pin 19
- connect SRAM pin 21 to CPU pin 22
- bend all pins on 74LS00, except power pins and piggyback it on IC15
- connect 74LS00 to PCB according schematic diagram
- solder new LS32, LS174 and GAL to universal PCB
- connect it to PCB according schematic diagram
- AR6new connect to separated AR6
- AR7new connect to separated AR7
- connect /CAS0 to /CAS on all original DRAMs
- connect /CAS1 to /CAS on all new DRAMs
- connect IC14 pin 1 to new GAL pin 14 (either bend pin 1, or connect it on PCB)
- cut IC9 pin 14 from /M1
- connect IC9 pin 14 to new GAL pin 16
- connect mode switch
Tips:
- you can modify Didaktik M also, just skip nonexisting parts
- be careful, Didaktik PCBs are very weak
Distinguish EPROM content:
- Kompakt with MDOS1 / WD2797: use KOM128S.ROM
- Kompakt with MDOS2 / 82C765B or equivalent: use KOM128N.ROM
EPROM banks:
- bank0: 128ROM_0
- bank1: K128_NMI
- bank2: 128ROM_1
- bank3: MDOS
.files.
- schematic diagram: 128k-rebuild-Kompakt-M.png
- ROM & GAL content: 128k-rebuild-kompakt-m-rom-gal.tar.gz
- description in slovak: 128k-rebuild-kompakt-m-popis.txt