Mega CD Multibios (w00t!)

[chaoticjelly]

I've fitted a multibios in my Mega CD.

I'm using bankswitching with high and low addresses, using a ON (OFF) ON switch (SPST centre off).

It seems to "work" - using the region and hertz modded Megadrive 1 I can get the BIOS from each region to boot up with the correct settings on the Megadrive

BUT

Just the background loads up..

There is no music
No animation
No message at the bottom of the screen telling you what to do

I was just wondering if anyone had any suggestions as to what could be causing this.. I have tried a hell of a lot of stuff, and im near certain that everything is connected perfectly.. my soldering is good.. just wondering what could be causing this as ive spent considerable time and effort but to no avail...

Ive been in contact with FABombJoy about this.. but I was wondering if anyone else has performed this mod and possibly encountered the same problem?

Thanks in advance..

[omnedon]

I have an eeprom burned, with the three BIOSes on it.

It worked in NA mode, but in UK and JP mode I would get the proper MEGACD screen, and no audio at all.

I did the same mod with the way overpriced, and not quite legal MultiCD BIOS mentioned at Eidolonn's Inn (customer supplied the eeprom) and it worked fine.

I suspect something odd with the eeprom burning (mine too), as the mod is reasonably straight forward, though not easy to perform.

[chaoticjelly]

Bleh..

Did you concatenate them and then byteswap?

I found the mod pretty easy to do... it just... doesnt work right :/

Theres no way im paying 40 euros for a chip, the guy that sells those didnt even reply to my email a few weeks ago when I enquired about buying one...

Its very strange I just dont know why the whole BIOS doesnt load up.. just the background...

I did get the jap text at the bottom of the screen when I turned it on once.. but only once.. and I didnt change anything I was just turning on and off.. on and off..

[omnedon]

You and I may find desoldering of IC's easy (with the right tools), but IMO, it's not for the greenhorn.

Anyway, I know a fellow with a burner, and he burned it for me, byteswapped. Don't know about the concatenate.

It's been languising, waiting for me to go back to it.

It's gotta be the eeprom. Why would it work *at all* if it was a trace, or install error?

[chaoticjelly]

Yeah I guess.. I asked FABombJoy if he could possibly send me his image so I can put it on a chip.. but im not sure if he'll send..

I didnt desolder that IC.. I just cut each leg with a pair of curved fingernail scissors.. took about 10 minutes then just soldered the IC socket on top of the "stubs" that had been left from where the pins were still somewhat stuck in...

Slightly messy.. but solid as a rock

[FABombjoy]

Man why does everybody have strange problems with this? I swear I've done a couple now and both worked just fine.

cj - PMed you about the file

[omnedon]

I have a professional desoldering station. Built in suction. Like an IC was 'never there'.

It's true Luke. We can't replicate your genius!

[chaoticjelly]

Desoldering station.. nice.. I wish I had one of those but I suppose they run to a few hundred pounds at least?

Yeah everyone seems to have trouble with this mod but im not paying for Sega's IP

I have another Mega CD I could try, but if that ends up the same, I wouldnt be very happy (I find Mega CD's one of the most difficult systems to find "in the wild")

Bleh...

[chaoticjelly]

It's totally wierd.. its like the mod is working, but the whole BIOS for each just doesnt load up..

All I get is the background...

GRR!

Occasionally the "Ready" light briefly flashes upon powerup, but only for a fraction of a second.. if you press reset on the EURO or USA modes, the system just black screens.

If you press reset on the JAP mode, the system reboots and the background appears all jumbled up, half off the screen, and sometimes you just get a blackscreen like the USA and EURO modes..

Does anyone have an Arakon BIOS I could buy?

[chaoticjelly]

WOOT!

I spent 1 hour this afternoon modding another Mega CD 1, the exact same way, and put in the same BIOS.

IT WORKS PERFECTLY!

I am ecstatic and a few minutes ago I was dancing to the tune of the "Sega CD" BIOS



So looks like when I slipped with a knife on the first Mega CD, I must of cut a track or two.. probably fixable.. not easy to do.. but better than discarding a previously working unit..

*IS NOW VERY HAPPY*



Thanks to FABombJoy and Omnedon for making this possible

[omnedon]

Broken trace did cause that eh? Time to check all the points on mine then. Maybe a pin seat was partially damaged on one or two, causing a broken trace.

Thanks for sharing your problem, and your solution! Exactly what this forum is for.

[chaoticjelly]

Nope.. what I mean is that I had two Mega CD 1 consoles.

I opened up another one this afternoon (previously untouched) and did the same mod as on the first one I tried..

That one works.. and both my burned BIOS chips work as ive just tried BIOS #2 now..

So the original Mega CD most likely doesnt work because when I first tried to cut pin 20 for the original BIOS disabling part.. I slipped with the rather large knife.. its possible that a trace or two could of been cut..

I'll have to try and repair that later... or re-try the mod..

But for now.. I have one working Mega CD multibios unit! :-)