Philips NMS 8250/8255/8280 mixing issues

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Van Huey

Prophet (2694)

afbeelding van Huey

11-11-2010, 13:53

Ah OK.

So I need to place 2 2200 Ohm resistors ( -[||||||]- ---- -[||||||]- ) on pin/cable 49 of the cartridge part leading to the PCB (main board).

That would be sweet as I cannot use internal and external PSG together on the SCC+ FLASH cart atm.

Van Wild_Penguin

Hero (644)

afbeelding van Wild_Penguin

13-11-2010, 14:38

Hi all!

Sorry for being away, too much work to do too little spare time for MSX ;-)

I see a lot of other people have mixing issues with their Philips NMS'es... but, I have to comment to Repair-Bas's comment:


The problem is this topic has to do with Flash SCC+ cartridge.
The problem is in the cartridge.

That, as the OP, in my case this is not the case ;-). Or =(. So, I'm a bit confused as there are a lot of posters - has anyone else than StepehnM noticed, that the MegaFlasRomSCC+ is different than an original SCC cart?

I haven't, and I have Pennat Race (although that one doesn't use the PSG at all? I did however once cover it's Pin25 and play with SD-Snatcher), F-1 Spirit, Salamander to test with =P. Every SCC cart, even the originals do not have audible PSG. Hear, I even made a recording of F-1 Spirit for you to hear (with the original cartridge) =).

Actually, I think (though I'm not sure) that when I first got the MegaFlashRomSCC+, I could hear the PSG at a very low level, and back then also in the original SCC carts the PSG was audible, but very low level (similar to MegaFlasRomSCC+, could not hear difference). But something has changed since then, since now it is totally silent, even though I haven't touched the insides of my MSX since :o. But, alas I can't be sure, as my memory is foggy - I could even remember wrongly when I changed the resistors to elcos on the AV board, it could have been after I got the MegaFlasRomSCC+.

Actually, as I did some more tests, it gets even more weird. I started to play in basic without no cartridge inserted - I noticed that PSG is very silent even when compared to the keyclicks! :-?. I need to do

PLAY"V12C"

to get an barely audible C and

PLAY"V15C"

to get an C at the level that it used to sound without any V in the play command (btw. what it the default volume?). It seems that most game carts that use only PSG (no SCC) sound correct, however (maybe they set the PSG to V15?). So, maybe my MSX mixing circuit has beceome broken in some other way?

However, once I have the time to get to open my MSX and do some testing I'll let you know what the conclusion will be =)

Van Wild_Penguin

Hero (644)

afbeelding van Wild_Penguin

13-11-2010, 15:22


That, as the OP, in my case this is not the case ;-). Or =(. So, I'm a bit confused as there are a lot of posters - has anyone else than StepehnM noticed, that the MegaFlasRomSCC+ is different than an original SCC cart?

My Memory is indeed foggy =). Answering to myself:

I did some more testing, by covering pin 25 of the SCC cartridges I have. I used Konami Games Collection for testing. There is indeed difference between cartridges:

I noticed, that with the MegaFlashRomSCC+, the PSG is inaudible (I need to crank up the volyme so that the SCC level is breaking my eardrums to hear very low PSG and a high FUZZ because the background noise is amplified). With Pennant Race, the PSG is barely audible (i.e. acan be heard in places where SCC is silent only). This is what I was remembering, with the SCC being almost (bot not quite) inaudible. With the Salamander, the PSG is just a bit louder, but still way too low. With F-1 Spirit, covering pin 25 does not work because for some reason the cart's SCC does not work with other software, and also the MSX boots "twice" (the logo is shown twice)... maybe the F-1 Spirit is mapped(?) differently and need some other pin(s) to be covered to be abused this way :D.

So, to summarize, even original Konami SCC carts have variation in their mixing. So I think there is nothing wrong with the MegaFlashRomSCC+, it just seems to be in the "loud SCC end" of the mixing. There's maybe some resistors inside the carts too, that have varying values?

Van Creepy

Champion (335)

afbeelding van Creepy

20-11-2010, 22:44

Just to confirm: I can hear the PSG at a normal level with the Megaflashrom SCC+ inserted with this fix Smile Thanks again Bart, Bas, and the others with helping.

Van Guillian

Prophet (3516)

afbeelding van Guillian

20-11-2010, 23:26

Nice to hear that! Smile

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