CX5M with SFG-05 Low Free Memory and "call music" Trouble

Not being experienced with the CX5M I probably won't be of much help, but at least one thing I know: The Z80 CPU used on the MSX has only 16 bits of address space, therefore it can only address 64kB at maximum without any tricks. The MSX architecture works around this by implementing slots, which can be both primary and secondary and there may be a grand total of 16 maximum (most MSX models have one or two expanded internal slots, with a few secondary slots, and two external primary slots). In the MSX-BASIC environment the MSX-BASIC and the MSX-BIOS both occupy the bottom 32kB of address space, while any available RAM can be found starting from the top address space. For this reason MSX-BASIC can only "see" 32kB at most, and will report around 28kB bytes free with no disk drives attached. If you have more than 32kB of RAM the MSX can still use it, but not from MSX-BASIC.

Since your CX5M only reports 12kB free without the memory cartridge, probably the onboard RAM is busted. I have no idea about the SFG-05 behaviour with the MSX keyboard, but I'm sure there's people here who can help with that.

It looks like one of the RAM chips inside the CX5M is out of order.

• Since the CX5M should have 32K of memory and Basic only reports about 12K free (16K missing).
• The internal software of the SFG-05 doesn’t work because it probably needs at least 32K.
• If you insert the RAM expansion, it fully replaces the internal memory, and given that it solves both of the two issues above, it affirms the suspicion that the internal RAM has a defect.

The YK-10 music keyboard shouldn’t interfere with the computer keyboard, but it could be that Yamaha’s software uses awkward nonobvious key combinations. Have you checked the manual for what you’re supposed to press?

What are you expecting pressing keys on the computer keyboard does? Sound notes as well? That they don’t do. They’re used for selecting instruments and polyphony, etc.

Ah, ok, then it is working as intended I think. I don’t recall my SFG-05 did any letter key playing, I always had to connect the MIDI keyboard. I think the SFG-05’s software may be a bit different from the SFG-01.

So there’s just the concern with the broken internal RAM chip…

Thanks for clarifying how the RAM expander works in conjunction with MSX BASIC. That leads to how a 64K RAM Expander could ever be useful if BASIC takes up half of the address space, but that's another question for another topic.

I was beginning to suspect bad RAM the more I thought about it. I opened up the CX5M just a little while ago, and didn't see any obvious damage to the board, any obviously damaged components, or any obvious failed solder joints. However, the symptoms still point to bad RAM... so I guess I'll be starting the search for some replacement chips.

As for the internal keyboard not working when using the SFG-05's built-in software: according to this page in the wiki, there are a number of useful keys available to change the synthesizer settings. I have not been able to get any of them to work (but those keys work in basic, so I know it's not the keyboard).

Here are several YouTube videos showing what I think I should be able to do on the internal keyboard:
Yamaha CX5M Part 2 - note that he is changing voices with the left and right arrow keys
Yamaha CX5M SFG05 - note they are able to change settings with internal keyboard

On my SFG-05, the arrow never flashes, none of the supposed hot keys work (not even the left and right arrow key on the default voice), and I don't see keys played on the screen. The YK-10 lets me play with the default voice, but that's it...