Sega Mega-CD II audio and memory format issues. Can Anyone help??

[mamejay]

Hey Guys,
I got myself a Mega-CD II in a lot of broken and working consoles.
The Console itself seems to be working OK except for the audio is really playing up.
This seems to be causing issues with games also. I have a few backups of different games which run fine in emulators but on the Mega-CD the sound is sometimes out of sync and really distorted.
One last thing is that I cannot format the internal memory for Sonic. I have replaced the battery and still have the same problems.
Any ideas about what this could be and a possible fix?

Have a listen to the title BIO screen on the unit
http://www.youtube.com/watch?v=CoHdmug7r2Y&feature=player_embedded

From what I have seen it should sound like this.
http://www.youtube.com/watch?feature=player_embedded&v=FWXKoxYZ1rc

[l_oliveira]

It's not a simple to solve problem but basically, the sampler chip (315-5476) has issues with it's communication with the sample RAM chips (2x 65256, PSRAM 32KB x2)

The backup RAM is a 6264 chip (8KBx1) controlled by a MB3790 (SRAM backup watchdog circuit) chip.

I suspect your machine might have corroded traces on these two parts (PCM sampler and SRAM backup) and it's what's causing your problems

[mamejay]

It's not a simple to solve problem but basically, the sampler chip (315-5476) has issues with it's communication with the sample RAM chips (2x 65256, PSRAM 32KB x2)

The backup RAM is a 6264 chip (8KBx1) controlled by a MB3790 (SRAM backup watchdog circuit) chip.

I suspect your machine might have corroded traces on these two parts (PCM sampler and SRAM backup) and it's what's causing your problems

Thanks for that.
I have checked the board and it really does look in good shape.  Would a continuity test of these chips possibly show these faulty tracks?
Also would replacing the CAP's have any effect in correcting this issue?  Could they be the problem?

Does anyone have a schematic for the MegaCD II or SegaCD 2?

[l_oliveira]

Thanks for that.
I have checked the board and it really does look in good shape.  Would a continuity test of these chips possibly show these faulty tracks?
Also would replacing the CAP's have any effect in correcting this issue?  Could they be the problem?

Does anyone have a schematic for the MegaCD II or SegaCD 2?

I would suggest you have the 65256 ram chips replaced if the motherboard is really on such a great shape...

The backup RAM not saving/formatting has to do with the battery but the sound issue has nothing to do with the battery.

[mamejay]

Thanks for that.
I have checked the board and it really does look in good shape.  Would a continuity test of these chips possibly show these faulty tracks?
Also would replacing the CAP's have any effect in correcting this issue?  Could they be the problem?

Does anyone have a schematic for the MegaCD II or SegaCD 2?

I would suggest you have the 65256 ram chips replaced if the motherboard is really on such a great shape...

The backup RAM not saving/formatting has to do with the battery but the sound issue has nothing to do with the battery.

I have replaced the battery so I suspect its something more to do with the actual ram itself.
Now the fun part.  Where to find replacement chips.