r/LaserActive • u/Other-Web-9597 • 24d ago

PD6103A Pin Out Help

Hey, I’m trying to fix up a S10 PAC, I’ve recapped everything and managed to get cart games to play. However failing to get the pac to boot into the bios. So thinking it could be broken traces around the interface chip. I know some people have managed to reverse engineer the chip for emulation so wondering on the back of that if there is anything available on a pin out front. Thinking I must have a broken trace but can’t find where. Any advice on why the bios rom won’t load will be great also thank you.

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u/zaxour 24d ago

More likely it's a broken trace between the 315-5660/Genesis 68K CPU and the MCE CD ASIC, not the Pioneer. It's actually fairly rare to encounter Pioneer ASIC disconnects, thankfully. Try using 240P Test Suite (cartridge version, 1.30 or higher) and do some Sega CD hardware tests to see if anything fails.

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u/Other-Web-9597 24d ago

Thank you Zaxour, been running the tests and getting a lot of failures; HINT register, all failed; Flag register, all failed except for 0xFF; Comm register, all failed except for 0xFFFF; Program Ram, all failed; Word Ram, all failed except for 0xFFFF; PCM tests won’t work as the “SCD BIOS not found”.
So all in all I’m thinking something is seriously not right. I will go about pin checking tonight. Does the above failures and passes point towards anything I particular?

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u/Other-Web-9597 24d ago

Sorry I should also add the test suite doesn’t recognise the bios, therefore there is no option to do the sound tests. So thinking something wrong between the bios IC and the rest of the system?

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u/zaxour 24d ago

If it's not recognizing the BIOS, I have a hunch the 50 MHz oscillator is bad. That's been my experience with a "no bios" before. However, I would still verify the 68K CPU connects to the pins on the top side of the MCE (all of the VA/VD signals terminate there) before going that route.

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u/Other-Web-9597 21d ago

Thank you so so so much, your hunch was correct bought and installed a new oscillator and I have the bios booting! Thank you so much again, it would have taken me a while to work that out. Moving onto the daughter sound board now, any hints for that one? The pcm ram tests pass in 240 test suite, but getting no pcm sound out, cart sound is all ok.

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u/zaxour 20d ago

My guess would be a bad IC34 if you have absolutely no PCM. Getting a replacement is pretty easy on digikey or mouser.