It looks like this thread has been dead for a long time, but I wanted to check in case anyone had learned anything new, and comment on an unanswered question.

If these units are all identical except for a single ROM IC, it should be possible to replace that IC with a customized larger bank switching IC such that an external switch would permit choosing the function of the unit. This has been done with various computers and game consoles to allow switching OS roms or games, respectively.

I would assume, however, that the battery backed memory would be lost and have to be wiped each time the function was changed, since the data format for each function would not necessarily be compatible (Strummer settings wouldn't work for the Cyclone, etc).

Next, there was a question in this tread about upgrading the memory in these units. This is documented in some of the manuals (Strummer and Drummer), so memory can be upgraded as follows:

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Memory Size
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Your Perf/X comes stock with 8K of RAM (Random Access Memory). It can be expanded to 32K of RAM allowing user patters to be recorded in all 100 presets/longer riff's to be recorded. While the procedure is relatively simple, caution against static electricity must be exercised to avoid destroying your unit. The services of qualified tech should be used to change the memory chip. In case of problems occurring after a memory expansion, Oberheim will make the sole determination as to the correctness of the procedure and the cause of failures in circuitry.

Memory Expansion: (works in ALL Perf/X)

To expand the memory, replace the memory chip inside the Perf/X with a 32K x 8 low power static RAM (SRAM) with a speed of 150nS or better. (The Hitachi part number for this is a UM62256A-15L. Other brands will work fine. The "generic" part number is 62256.)
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These chips appear to be available, on eBay for example.

A quick look inside my Strummer reveals an HY6264LP-10 chip currently installed, which appears to be the standard 8K RAM. Once I get this unit backed up, I plan to upgrade.

I don't see any mention of the RAM upgradability in the manual for the Cyclone, but the section in the Drummer manual does say _ALL_, so if the 8K IC is there, the Cyclone should be upgradable too, presumably increasing sequence memory.

Finally, my Strummer has a card slot that is populated by the appropriate card end (male) but I have no idea what fits in this slot or what it would be used for, and can find no mention in the manuals I've looked at so far.

Cheers