NMS-8280 megaflashrom sound problems

Resident (44)

20-01-2020, 18:41

Hello MSX friends,

I have a NMS-8280 adapted to a 2+. All soundcard work fine (MM, FM-PAK, OPL4)
But when I put in my Megaflashrom all cards won't work even the PSG. The PSG on MFR does work with Konami roms with the /p function. SCC also works fine, but MSX-MUSIC and AUDIO doesn't work
I know there is a similar post with this problem, but the conclusion is to change condensers. I don't think this is the problem because the other audio is amplified and mixed ok.

Anyone had the same problem with MFR? Or with other cards? If an other mass storage device works better I will use this instead. And use the MFR in my other MSX.

By DrWh0

Paladin (842)

20-01-2020, 18:53

Hi BiT,

Try using /P1 parameter to clone psg to the cart (not /P) also you can try this solution (8250/8280 are very similar):

https://www.msx.org/forum/msx-talk/hardware/sound-issues-on-...

By Wild_Penguin

Hero (644)

20-01-2020, 20:02

Yeah, the NMS825X have a crappy amp circuit by design. The NMS8280 is no different according to it's service manual. See page 23 and the Wiki of any of these computers for options. The OPAmp mod by Luppie is the one I have in my 8255, however at that time I didn't know about the fix you can find floating around and on the net, for example this page: https://www.retromsx.com/#page-top .

I noticed that the SCC attenuation will depend quite strongly on which SCC cart you have inserted on this computer; I mean just a different SCC game had slightly more volume than another (all gravely attenuated so that SCC volume is very low compared to PSG). The MFRSCC+SD indeed suffers most of this design fault on the NMS8250/55/80, even more than any of the original SCC carts I had (when I still had the faulty circuit...)

Don't use two external sound sources in an NMS8280 (or 8250/55 for that matter) at the same time, unless you know the sound mixing has been fixed. It won't work, as their sound inputs are just connected together. If I'm not mistaken, this can actually damage a sound cartridge (IIRC I've seen this mentioned somewhere; I have no idea how likely this will cause some damage to a cartridge).

By BiT

Resident (44)

20-01-2020, 21:24

Thank you for your answers DrWho and Wild_Penguin. Seems I have to work on my soldering skills after all. Or don't use the MFR in my 8280 and only use cards with their own output.

By Wild_Penguin

Hero (644)

23-01-2020, 19:24

It is perfectly safe to use the MFR as long as you don't use another sound expansion at the same time. You may get useful sound (correctly mixed) if you patch the games to use the internal PSG of the MFRSCC+SD (SofaRun can do it for you, or use switch /P in opfxsd - IIRC: check the documentation...).

FM expansions are probably out of question on that computer (without mods)...

By BiT

Resident (44)

23-01-2020, 21:27

FM expansions don't work indeed. So I really think I have to mod this MSX. So probably a mod to the whole sound circuitry for as far as I read in other posts. Don't think only changing condensers should work.

I found out that the /p option only works with Konami roms and the /p1 option with all other kind of roms.

Anyway it's a strange bug in this machine, if you think it's one of the best and most expensive Philips computers back then.
But I love this machine for the video capabilities, and would be best to run all soundcards in combination with MFR and Symbos. It's already modded to a 2+ so this could be a super machine!

By meits

Scribe (6577)

23-01-2020, 23:24

8280 is a great machine and has a lot one would want back in the day.
When it was designed, only PSG and MSX-Audio existed. I can imagine they never thought this would bite them in the back.

By Wild_Penguin

Hero (644)

24-01-2020, 08:49

IIRC I've red these machines were mostly targeted at businesses; but correct me if I'm wrong ... this is something I've learned in more modern times, probably from these forums. As such, most buyers probably didn't care / weren't aware of the mixing issue (when they were sold as new).

If you know a bit of soldering, it is trivial to fix with the instructions (or take it to a trustworthy friend). After that, these are excellent MSX2s!

By gdx

Enlighted (6440)

24-01-2020, 10:43

Components are just badly positioned. Get new components and put them back in the correct position. It's not difficult and you will be happy.
If you don't know how to solder at all, ask someone's able among your acquaintances or on the forums to do it at an MSX convention.

By Wild_Penguin

Hero (644)

24-01-2020, 15:43

gdx wrote:

Components are just badly positioned. Get new components and put them back in the correct position. It's not difficult and you will be happy.

Gdx: if you mean just to swap capacitors, which are sometimes the wrong way from the factory, compared to the circuit in the Service Manuals (don't remember if the silkscreen marking is right or wrong); that is definitely not enough! The PSG/SCC(or other sound expansion) balance will still be way off. Not to mention it does nothing to shorting the inputs of cart1+cart2! The circuit on the MB is practically broken by design.

Take a look at the instructions at retroMSX page I've linked for example. Five resistors and two capacitors need to be added to the circuit to reproduce NSM8245 circuit. This is the simplest mod I've seen to make an actually correctly working circuit, with correct balance and two usable cartridge slots (haven't tested it, though). It can be done on the MB, by the looks of the PDF. Luppies mod is even more involved, and requires the PCB designed for it or a protoboard PCB. It's a bit more involved, but still very basic soldering, nothing special.

By BiT

Resident (44)

24-01-2020, 17:20

Do you know if this pdf exists in English? I did some basic soldering before, but this looks way more difficult. And I don't like destroying my MB or sound expansions. Besides I would like to know exactly what kind of resistors an capisitors I have to use. Is this the only detailed documentation for this issue?

Would be nice to make a tutorial by myself if I only knew what to do haha