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

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Por jdmcs

Rookie (22)

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30-05-2018, 05:32

I recently purchased my first MSX system: a Yamaha CX5MU with a built-in SFG-05 synthesizer. It arrived poorly packaged, and despite the shipping box being in the rain for an hour or two (no thanks to FedEx Home Delivery being slow to update tracking info online), the water didn't seep inside the box and everything seemed to be intact.

Fast forward a week because I had to wait for the video cable. The F1 key was stuck, but it luckily it turned out to be an easy fix (canned air). Now, I'm trying to get the SFG-05 synthesizer to work correctly. I'm hoping someone might recognize the symptoms:

  • If I power the CXM5 with only the SFG-05 cartridge installed, there are only 12431 bytes reported free on boot.
  • If I try to "call music" with only the SFG-05 cartridge installed, the CX5M appears to lock up as soon as I hit enter.
  • If I power the CXM5 with the SFG-05 installed and a Casio OR-264 64K cartridge (the only one I have) inserted in the top slot, 28815 bytes are reported free on boot (what I expected to see with just the SFG-05). [I had expected closer to 60K free to be reported.]
  • If I "call music" with the SFG-05 and the OR-264 cartridge, the music screen appears and the synthesizer plays notes when keys on the YK-10 are pressed. However, there is no response to any of the QWERY keyboard keys.
  • The contacts in the top cartridge slot look fine (doesn't seem as if anything is shorted when no cartridge is inserted).
  • And yes, all of the QWERTY keys seem to work from basic.

My initial thought was that the SFG-05's EPROM was blown, until I got "call music" to start to work with another cartridge inserted. Now I'm wondering if it could be a power issue, though I don't see how adding another cartridge would help if power was out-of-spec to begin with, or possibly bad RAM (just got the Casio cartridge today).

Do these symptoms sound familiar to anyone? And could you point me towards an area to look, especially if my guesses sound incorrect given the symptoms?

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Por Parn

Hero (608)

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30-05-2018, 15:55

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.

Por sdsnatcher73

Paragon (1198)

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30-05-2018, 16:07

I’ll check this evening if SFG-05 bios should react to keyboard keys. What you may try is disconnect the YK-10, as it may only react on the internal keyboard if no external keyboard is connected.

Por Grauw

Ascended (9379)

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30-05-2018, 16:18

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?

Por sdsnatcher73

Paragon (1198)

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30-05-2018, 18:21

Well on my SFG-05 there is no response to key presses on the internal keyboard either. I guess it's just how it was designed...

Por Grauw

Ascended (9379)

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30-05-2018, 18:38

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.

Por sdsnatcher73

Paragon (1198)

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30-05-2018, 19:36

Well I think I remember SFG-01 does play notes on letter keys. And changing polyphony is done with function keys and instruments are changed through cursor keys...

Por Grauw

Ascended (9379)

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30-05-2018, 22:10

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…

Por Manuel

Ascended (17061)

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30-05-2018, 22:18

I also had a problem that I couldn't get the SFG to play anything without an external keyboard. Very annoying when I wanted to test the YM2151 emulation in openMSX, as the external keyboard wasn't (and isn't) emulated...

Por jdmcs

Rookie (22)

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31-05-2018, 05:46

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...

Por jdmcs

Rookie (22)

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31-05-2018, 06:23

Also, I tried using MIDI In for playing the SFG-05 synthesizer, since that is what is being done in several of the YouTube videos I linked. No dice -- the internal keyboard still doesn't respond to change voices (or anything more complex).

(Could the SFG-05 ROM be coded to assume it would only ever be using internal RAM and not a RAM expander? I guess I'll know once I receive the "new" memory chips I just ordered.)

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