The Plus/4 was bought "sold as seen" on eBay and doesn't produce any video output. So, I'll need to work on fixing it. It needs a good clean both inside and out.
The Yamaha CX-11 was sold as working. It powers up fine, and "call music" goes into the Yamaha ROM, allowing playing around with voices and apparently control via MIDI.
Other than a basic test, I've not had time to play with it. It also needs a good clean.
I've not been able to find out much info on the CX-11. It seems like a slight variant on the much more common CX-5M. It has the SFG-05 unit, instead of SFG-01, RGB out, two normal MSX 50 pin slots as well as the Yamaha 60-pin side-slot with the SFG-05 fitted. Apart from this, it seems very similar to the CX-5M and YIS-503, but looks like the CX-5M II. It's a standard MSX (not MSX2), with 32K RAM and 16K VRAM. I've not popped it open to see what's inside yet. I have the CX-5M and YIS-503 service manuals, and they should be handy for comparison. I also recently received the MegaFlashROM SCC+ SD (with 512K RAM). With this, I should be able to load ROMs for the original Yamaha software and play around with this.
The SFG-05 uses the YM2164 (OPP) chip, which is apparently pretty much identical to the YM2151 (OPM).
I also bought a few Y8950 chips. This audio chip was used for the MSX-Audio FM synth standard, as available in some expansion cartridges. According to Wikipedia, it is similar to the YM3526 (OPL/OPL1), with added ADPCM sample and playback. I might build an MSX-Audio board, or hook them up more directly, perhaps to some homebrew kit too.
There is also MSX-Music, which is based on the YM2413 chip (OPLL, stripped down OPL2). Most MSX2+ machines had MSX-Music, including my Sony HB-FX1DJ. From what I understand, this should be a slightly more capable FM synth, but lacks ADPCM.
