Have been looking for one of these for a while, and finally managed to buy one for a mostly OK price. Here is a writeup on these things since there’s not that much available online.
High level features
CZ-6EB1 expands a two-slot X68000 into a four-slot computer, by plugging in an expansion card into the X68000 which routes two flat cables to a breakout box containing four IO slots. This likely works similar to how it’s done in a X68000 Pro.
This box has a separate PSU for the four cards, since powering the cards over the flat cable would not be feasible. This PSU will only power the card when power from the host machine is detected, otherwise the device stands in “standby” mode.
I bought a photocopied manual for these in a separate auction, which I’ve scanned and made available here.
Internals
The IO breakout board which plus into the host machine has only two connectors wired to the edge connectors. There’s no other circuitry on these.
These plug into the main board of the CZ-6EB1, which is called K5414DE. This board has a section near the flat-cable connectors which seems responsible for switching the power to the I/O cards on/off. There are two CK2605 PLD’s at IC1 and IC2, which I should probe with a logic analyzer and dump at some point.
I suspect the IC2 is responsible for the power management, while IC1 handles IRQ/ACK signals across the four slots somehow similar to how it works on the X68000 Pro.
There’s nothing particularly interesting about the PSU. There’s quite a lot of glue on some of the caps which makes recapping awkward but doable.
Recapping / cap-list
I decided to recap this thing, and found some sketchy looking caps which had started to leak so that was a good idea. The full cap-list is below. Something mostly similar in size will work, since there’s a lot of space available.
PSU
| Cap | Capacitance | Voltage | Dia x H (mm) |
| C706 | 330uF | 200V | 30×26 (snap-in) |
| C709 | 22uF | 25V | 5×11 |
| C710 | 4.7uF | 50V | 5×11 |
| C714 | 3300uF | 10V | 16×30 |
| C715 | 3300uF | 10V | 16×30 |
| C716 | 3300uF | 10V | 16×30 |
| C718 | 2200uF | 6.3V | 13×20 |
| C719 | 470uF | 16V | 10×20 |
| C720 | 4.7uF | 6.3V | 5×11 |
| C721 | 2700uF | 25V | 16×30 |
| C724 | 470uF | 16V | 10×20 |
| C725 | 470uF | 35V | 10×30 |
| C726 | 22uF | 25V | 5×11 |
| C728 | 100uF | 10V | 5×11 |
Main board
| Cap | Capacitance | Voltage | Dia x H (mm) |
| C1 | 100uF | 10V | 5×10 |
| C2 | 100uF | 10V | 5×10 |
| C3 | 47uF | 16V | 5×10 |
| C4 | 47uF | 16V | 5×10 |
| C5 | 10uF | 16V | 5×10 |
| C6 | 10uF | 16V | 5×10 |
Hooking things up
Getting things working on a regular 10Mhz X68000 is quite simple.
- Plug the card into Slot 2 of the X68000 and mount the back cover
- Connect the FG terminals on the X68000 to the CZ-6EB1
- Insert expansion cards into CZ-6EB1
- Power on the CZ-6EB1. It should have a red LED indicating standby
- Power on the X68000, the CZ-6EB1 will wake up as well.
RAM incompatibilities
When connected to a CZ-600, I could plug either a XSIMM10 or a Etarikashikoshi into the expansion unit, and have them be detected and work properly when running Memtest. Using a Nereid as RAM expansion did however NOT work, and kept giving me memtest errors. It works fine without the expansion box, so something was weird there.
With a X68030, I was unable to get any RAM card to work through the expansion box. The memory gets detected, but memtest shows failures, and games will not run well.
The manual only states that CZ-600 (10Mhz) is supported, and I could definitely see the higher clock rate causing these issues somehow.
Using other I/O cards like MIDI did work with this when connected to a X68030, but since the manual states that the internal Slot 1 cannot be used when the CZ-600 is hooked up, this limits the system to the internal 4MB RAM. Maybe that can be worked around somehow. Not sure.
Should you buy one / Other options?
Buying one of these is only really worth it for the “cool factor”, since it looks awesome next to a X68000. It being limited to 10Mhz for RAM means that the more sane option for having four slots is just to buy a X68000 Pro, which will cost less than just the expansion box.
Another four slot option is “Xpander IV” which extends the XVI Model with an internal four slot expansion. This looks real cool, but was not an official product and seems extremely rare. See: https://akiba-pc.watch.impress.co.jp/docs/wakiba/find/745817.html
Potential future projects
I haven’t seen any real documentation on how the conversion from two to four slots actually works. There’s a japanese blogpost which shows a DIY option, and references “Monthly I/O October 1991” as having some information. That would be nice to track down. Otherwise I might just see if I can reverse engineer how this thing (or the X68000 Pro board) works.
I am also curious if it would be possible to use this, while having RAM connected to the internal Slot 1 of a X68030, and that way bypassing the RAM issues. The manual does explicitly state to not use that port when the IO box is in use, so this is unlikely to be a good idea. Additionally, physically fitting a card in there is tricky when the IO-box extension is in place.
