Solved Any Sega system C/C2 experts here?

Georgian2

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Hello,

My system C board is almost converted to C2. Still some resistors and capacitors missing. So far I got games like Thunder Force AC and Puyo Puyo running on it without problem. I used 5x27C040 for all the roms. No voice or oder effects are present because of the missing parts.

The Inchant-R, Tant-R and Ribbit are not working and I can't figure it out why. All the jumpers are set in the right way. At first there is some activity on all the eprom address pins and data pins but only for like 2 seconds and that's it. I did replace the rams with 62256 and moved the one resistor in the right position. I also did the reset mod on the D7750 and the YM ICs.

Anybody has any ideea if these games work without the C2-sound part of the PCB??
I used decrypted roms that I found on the internet.

Thanks a lot,
Georgian.

Jumpers system C: https://forums.sonicretro.org/index.php?threads/system-c-hardware.38841/
 
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Georgian2

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Today I got all the remaing parts and populated the board. It still didn't work. After some more googleing I found that the system C2 uses an different revision on the IC24. I flashed another GAL with the right revision and it booted just fine.

I'm still missing an resistor value for the R21. If you have an C2 please post an foto or measure the resistence.
IMG_20250527_191029.jpg
Problem solved. R21 is 36K
 
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