Help to interchange a Sonic 3 ROM to a SEGA 171-6279A board

[crissaegrim87]

Well, as the title says, I have a sonic 3 ROM chip that transplanted to a sega 171-6279A board. As of now the game plays fine and save normally. But if i put into a S&K cart, it is completely ignored. I do have a bootleg sonic 3 wich is recognized perfectly by S&K. All the traces in the cart are good, no corrosion or anithing. Any ideas?

[TmEE]

I'm pretty sure this is because of the simple mapper on the PCB you used. Sonic3 has switchable SRAM visibility in the 2nd MB of ROM space, while the board you use has SRAM always visible. I'm pretty sure S&K cart requires ability for SRAM switching to work right.

[crissaegrim87]

I'm pretty sure this is because of the simple mapper on the PCB you used. Sonic3 has switchable SRAM visibility in the 2nd MB of ROM space, while the board you use has SRAM always visible. I'm pretty sure S&K cart requires ability for SRAM switching to work right.

So if I disable sram manually will it work? With something like a dpdt switch?

[crissaegrim87]

Ground/5v to CE will be enoug? does it erase the saves?

[TmEE]

No, this is software controlled stuff. You need to recreate the circuit on the original Sonic3 cart, which uses a 74x74 to hold one bit that controls if SRAM is visible or not, triggered by writes to $A130xx range (signalled by !TIME on the cartslot)

[crissaegrim87]

Oh, too bad . So no chance doing that I think. Maybe checking what/what not is present besides the pair of 74*74 and the traces. I was planning to build a SMS phantasy star using an afterburner as a donor, soldering the sram chip and the backup circuit. I think this sonic 3 conversion is beyond my understanding. Thank you for your time.