NMS8250 no sound with megaflashrom

Página 2/2
1 |

Por sdsnatcher73

Prophet (3527)

Imagen del sdsnatcher73

04-01-2022, 14:58

Ah, the inevitable I have this but where did I put it… next step buy a new one because you can’t find it… next step you find it once the new one arrives Wink

Anyway, please report the results as I think many people are interested in them!

Por Wild_Penguin

Hero (644)

Imagen del Wild_Penguin

04-01-2022, 15:02

The fix from Bas is only a partial fix. I believe it will only fix some distortion from the internal audio sources (PSG and PPI) but IIRC it will do only a little to external audio sources like SCC and FM cartridges. My memory is really hazy but I did have this fix, including changing the resistor value, but external sources were still way too quiet; case may be I just didn't have a working resistor value after all.

And, indeed the audio outputs will be shorted together, which is bad if you have two audio extensions plugged in simultaneously at any time.

The fix with the Spanish instructions, inspired by the NMS8245, will be the most easy proper fix, but you may try the one made by Bas and see if it will work for you, since it is really easy to do. I believe the problem with that one is that the impedance (????) of the sound expansion cart audio input will effect the ratio of the volume it will mix with the internal sound (ahem this is coming from a non-electrician!). This means there is no single resistor value which will work for all sound expansions. This means: it might work with original SCC carts, but not FPGA implementations and/or FM carts...

I ended up doing the mod using an OpAMP years ago, but the Spanish instructions based on 8245 were not available at the time. That one is much easier than the OpAMP mod, which will require an additional PCB. I used a protoboard :-).

Por sdsnatcher73

Prophet (3527)

Imagen del sdsnatcher73

04-01-2022, 15:14

The issue with the 8250 is actually that the internal PSG is muted once a sound cartridge is attached (even if it is not used). So the fix from Bas is to alleviate that (and probably works to a certain extent but probably not as good as the Spanish variant) but indeed it cannot fixing the shorting that will occur if two cartridges with sound input are attached.

Página 2/2
1 |