MegaFlash SCC+ no audio at all with several games

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By Repair-Bas

Paladin (958)

Repair-Bas's picture

18-03-2011, 15:03

Is it not the easiest way to put in a resistor of 2K2 in the cartridge on pin 49?
Then I think all problems are solved.

By olliraa

Champion (278)

olliraa's picture

18-03-2011, 20:12

Ok, thanks for the input guys Smile I just got back from a day long retro computer/console exhibition we held on the campus Smile Smile

@Daemos: It would be great to get the schematics (email is available in my public profile). I think I'll handle the work to a friend of mine, who's very good at soldering Smile Just one more question: What is the difference between "adding one resistor -mod" and Daemos' "adding an opamp + other stuff -mod"? Sorry, Ij ust have to consider the amount of work compared with the gain Smile

This forum/community is just great. Although I'm pretty new here, I always get the advice I need. Just great Big smile Thank you!

By Daemos

Paragon (1649)

Daemos's picture

19-03-2011, 00:16

The big difference is the crosstalks you will hear when just adding the resistor. I have tried that one and it fixes the problem but the crosstalks are kinda terrible. The sound will also be attenuated at a level the backround noise of your television becomes pretty audible.

The opamp fix simply does what every other MSX does. It actively mixes down both signals and amplifies them back to normal levels before the signals go into the analogue board. The thing the mod doesn't do is fix this for both slots when used at the same time. For instance you trow in a FM-PAC and the SCC+ at the same time.
I figured I would never do that anyway so I didn't incorporate that in my design to save up boardspace.

@creepy: I couldn't find your email adress. Help me out with that one so I can mail you the schematics

By Creepy

Champion (324)

Creepy's picture

19-03-2011, 12:03

Weird, my mail address should be visible. Anyway: it starts with creepy and ends with tweakers.net and in between goes the at sign.

The crosstalk, even without the resistor, is audible. When using a playsoniq cart the audio out on that cart has lots of noise. I'm hoping this will fix it.

By Daemos

Paragon (1649)

Daemos's picture

19-03-2011, 12:17

All sent. Including Creepy. If you have any questions I am all ears. You can just mail me about it.

By olliraa

Champion (278)

olliraa's picture

19-03-2011, 22:17

Thanks for the schmematics Daemos Smile

By iainjh

Supporter (15)

iainjh's picture

20-03-2011, 03:57

Hi daemos! please could you mail me the schematic too? I have the exact same cart and 8250 and symptom. thanks!

IAIN (underscore) hancock (at) hotmail (dt) com

cheers!

By luppie

Paladin (787)

luppie's picture

20-03-2011, 12:58

This is daemos schema:

upload.luppie.net/uploaded/audiofix.png

By Daemos

Paragon (1649)

Daemos's picture

20-03-2011, 13:12

Thanks for posting Lupie.

I see something in the schematic that is maybe going to be misunderstood.
MB1 and MB2 in the schematic is the connector that comes FROM the MSX mainboard. So you have to disconnect the connector that is plugged into the MSX analogue board connector AB and connect that to connector MB1-2 in the schematic. From your freshly soldered board (schematic) you draw a connector plug from AB1-2 TO connector AB on the analogue board of the MSX.

By luppie

Paladin (787)

luppie's picture

20-03-2011, 19:39

I took the liberty to draw this schematic in EAGLE, to create a PCB for it.
EAGLE Project files : http://www.luppie.net/files/Geluidsaanpassing%20NMS82__.zip

Schematic:
upload.luppie.net/uploaded/Schermafbeelding 2011-03-20 om 19.27.32.png

PCB Layout:
upload.luppie.net/uploaded/Schermafbeelding 2011-03-20 om 19.27.49.png

Components Layout:
upload.luppie.net/uploaded/Schermafbeelding 2011-03-20 om 19.28.25.png

Top Layer:
upload.luppie.net/uploaded/Schermafbeelding 2011-03-20 om 19.29.29.png

Bottem Layer:
upload.luppie.net/uploaded/Schermafbeelding 2011-03-20 om 19.29.47.png

Also did some calculating and to make this PCB incl. components and cable's to connect it is in total 15 Euro.
(This is with a minimum amount of 12 pieces)

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