SEGA System 16B - Shinobi Repair:
I recently had the opportunity to pick up this arcade PCB that I had wanted for a long time at a very good price. However it was listed as having sound problems and for some reason had been returned by a previous buyer. The only thing I had to go from was the following images:
So I decide to contact the seller to try to get some more information and got this reply:
I had it returned not working only to find the rom chip had be taken? So my mate replace it with a spare rom top left hand side the music works fine it just when it says Mission 1 and when you jump up a buzz noise comes on and goes off if my mate had a eprom programmer he can do it?
I could see that the suicide battery Z80 processor with sound encryption had been replaced by a regular Z80 and that position A10 on the ROM board had been changed to an EPROM that is labeled: Shinobi A7 Sound Fix.
This seemed a little odd. Was the wrong sound fix applied?
However I could see it was obviously booting from the provided photographs and while I was still dubious about its state and the story I decided to risk the purchase.
It arrived pretty quickly and indeed it had sound issues.
I could now see that the ROM PCB was a 5521 version and going from the Mask ROM positions I could deduce that this Shinobi was a Set 4 revision and this revisions suicide sound fix is a little different from the other game revisions and requires the non-encrypted epr-11361.a10 ROM from Shinobi Set 5 to work correctly.
I pulled the 27C256 EPROM from position a10 and dumped its contents with my TOP3000 USB universal programmer. The resulting binary had a CRC of 457A7CF which matches the CRC for the EPR11287.a7 decrypted sound ROM binary which is incorrect for this board!
So I erased the EPROM, then re-programmed it with the correct a10 code with a CRC of 1F47EBCB and now all the sound issues are fixed!
However…
To enable FREE PLAY on SEGA System 16B you need to push all 8 DIP Switches of DIP Switch 1 to on but after doing so the game was not booting into FREE PLAY mode so something else was up.
I turned on all the DIP switches on both DIP switches:
Then I proceeded to go into the Test Menu to check to see what Shinobi was reporting as working:
DIP Switch 1 switches 5, 6 and 7 were having issues and were reporting they were turned OFF still.
Flipping the board over I could see excess Flux that had not been cleaned up on the solder pads for both DIP Switches which leads me to believe that these have been tampered with at some point:
I used my multi-meter to test the continuity of all the turned on switches and they all reported back as good so the switches themselves are not the problem here.
I now suspected that there may be some broken traces underneath DIP Switch 1 and with the help of a SEGA System 16B schematic I found online I was able to tell that the DIP Switches connect directly to a resistor array 1 for 1 and then into a 74LS257 TTL IC:
Fortunately after testing continuity between switches 5, 6 and 7 I found that the traces between the switch and the resistor array was broken, so using some Kyna wire I bridged the connections on the bottom of the PCB:
Not the cleanest job but good enough to test and we have success:
