MK Slotexpander V3.0
This page was last modified 14:53, 13 January 2022 by Mars2000you. Based on work by Gdx and Grauw and others.



The slotexpander expands your slot into 4 subslots. These are numbered from 1 to 4. The one which is closest to the switches (this is the front) is number 1, the one on the other side is 4. The ones between are 2 and 3.

Although the subslots are numbered from 1 to 4 on the expander, the computer really sees them as subslots 0 to 3.

Every slot can be turned off. This is done by the dip switches on the front. To the top they are on, to the bottom off. The I/O ports still work in the off position.

This slotexpander has support for an external power supply, but no connector is present by default and has to be soldered in by the user.

The explanation for the version numbering can be found in MCCM issue 70 (page 32). Basically the initial version was designed by R. Stevens of the MSX Gebruikersgroup (User Group) Tilburg and demonstrated during the MSX fair Tilburg in April 1991. The rights to it were bought by MK.

However this first version had two problems, the BUSDIR and EXTINT signals were not properly implemented, causing problems with some interactive cartridges and the maximum distance was just 20cm. By June 1991 R.Stevens designed a SMD version which was meant to solve the issues. An initial batch of 25 PCBs was created. However when Thomas Manders was asked to actual assemble them he found during testing that they only had a maximum distance of 10cm. Eventually the issue was found and fixed, and these 25 versions were sold at the MSX fair Zandvoort 1991 as the MK Slotexpander v2.0.

With this knowledge, Thomas made during November 1991/January 1992 the new version 3.0 with a maximum cable length of 75cm. After MK stopped, Thomas made a v3.1 which solved an issue where the external power supply could cause interference due to power fluctuations, and replaced the dip switches with separate switches, and added a switch to switch between simple port extender and slot expander.

The hardware design was by Digital KC.


MK Slotexpander 3.0 with PSU
MK Slotexpander 3.0
MK Slotexpander 3.0 advertisement

Known issues

  • FM “stereo” PAK: the internal software is not working, unless a RAM cartridge is inserted in the expander.
  • Metal Gear 2 - Solid Snake will only work within a primary slot, but works fine when inserted in subslot 4 of the expander and no RAM cartridge is in the expander.
  • Snatcher Sound Cartridge doesn't work in this slotexpander, probably because of the flatcable length (weaker signal). Use in primary slots instead or confirmed: Snatcher Sound Cartridge does work in Carchano slotexpander (without flatcable) and Modulon (also without flatcable)
  • ESE-SCC cartridge does work in MK slotexpander, but only in subslot 4 and without Sunrise CF-ATA IDE cartridge (use Megaflashrom SCC+ SD for storage instead in primary slot)

Repair / upgrade