Changing the inbuilt game in a Master System Mk1

[John_Smith]

B) Alright!!! My first post!!!

Hi all!

I've been tinkering with my PAL SEGA Master System Mk1 the past couple of days and after strapping on some S-Video, C-Video, audio jacks and 50/60Hz switch I thought, "Hey, what about livening up the inbuilt game factor" coz 'HangOn' is kinda dull. I figure by de-soldering the on-board ROM chip and popping in a 28/32 pin socket, then either sacrifice a cart for the ROM chip or even just program a compatible EPROM with the game of my choice, I could pop it into the socket and have a decent inbuilt game as standard.

Now, I haven't actually tried this yet so I dunno whether there are other factors that would prevent it from working. Also I noticed while taking apart numerous carts last night that the games seem to use either a 28 or 32 pin Mask ROM (not sure if there's any that use a larger chip again). The Mk1 SMS has a 28 pin chip in place for HangOn, but I noticed it has the additional room for a full 32 pin chip/socket left unused. There is also a factory soldered jumper wire just above the on-board ROM chip labelled "JP1". It looks like it might have something to do with using/not using the extra 4 pins and this is my main query, does anyone know whether I'd need to remove this jumper wire to let me use the full 32 pins??? (Maybe I should take a digi photo of the area in question on the PCB for those without an SMS Mk1 in front of them...tehehe.......hrmmm)

Any help would be great!!

Cheers!!  

[blackevilweredragon]

Yea, I would need a picture, to see what you are talking about..  The lowest Sega console I have is a Genesis..

[viletim!]

I noticed a thread about this on the SMSPower forums the other day.
http://www.smspower.org/forums/viewtopic.php?t=9123
It seems the rom contains more than just a game.

[blackevilweredragon]

I noticed a thread about this on the SMSPower forums the other day.
http://www.smspower.org/forums/viewtopic.php?t=9123
It seems the rom contains more than just a game.

I figured that would be the case, just like the BOOT ROM in the Genesis decides to boot from Cartridge, or if no cartridge, then the EXPANSION bay..

[NFG]

It seems really odd to me that a ROM would be used to detect the presence of a cart or not.  In fact, it seems downright silly, all the system needs to do is use the cart-detect pin to activate the internal boot ROM (or not).  Why use code?

[edit] Well, I guess it makes sense if the boot-ROM is also checking the cart for legitimacy, as the Genesis/MegaDrive does, but the Master System never did this, did it?

[blackevilweredragon]

It seems really odd to me that a ROM would be used to detect the presence of a cart or not.  In fact, it seems downright silly, all the system needs to do is use the cart-detect pin to activate the internal boot ROM (or not).  Why use code?

[edit] Well, I guess it makes sense if the boot-ROM is also checking the cart for legitimacy, as the Genesis/MegaDrive does, but the Master System never did this, did it?

I got this information from another page, I have it on history on my laptop..  It was a discussion on Genesis with 32X and Sega CD (and how they all interlinked with each other, and how the boot ROM on the Genesis determined which was to actually be used)

For the master system, I would assume it would also be the case, since it seems that the Master System and Genesis have some things in common (especially Genesis SMS compatibility)...


EDIT:  I agree that using the boot ROM would be a waste of time to do such a thing, but it seems that Sega did infact do so, and I suspect they did the same on the Master System...

[Endymion]

[edit] Well, I guess it makes sense if the boot-ROM is also checking the cart for legitimacy, as the Genesis/MegaDrive does, but the Master System never did this, did it?

It did not do this for legitimacy--but it could have. Plug up a Sega Master System converter and a game to a MegaDrive (or a Genesis with a JP switch) and you will see several games that show a MARKIII or SEGA Logo at boot time--something you'd never see with the same carts on the Master System. The one time I opened up my old SMS I also recalled spotting a couple of points labeled "JP" in the age-old jumper methodology. Some games even change their content: Power Strike becomes Aleste for instance. I guess they hadn't experienced rampant piracy to the point of requiring the check back then though.

[John_Smith]

WOW!!! Thanks so much for the help with me query guys; I never expected so many well informed responses!!

I took a look at the suggested thread at SMS Power and yep that sorts me out pretty well. I did manage to at least replace the oh so crappy 'HangOn' in my SMS Mk1 with 'Alex Kidd in Miracle World' from my Mk2 though, which is a minor victory at least. I'll consider the addition of a manual switch to select the inbuilt ROM or cart slot routine though. Food for thought

Thanks again!