Old Famiclone poor compatibility - what could be the cause?

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Famicloner
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Joined: Sat Jan 22, 2022 3:13 am

Old Famiclone poor compatibility - what could be the cause?

Post by Famicloner »

I have a NOAC (glob top) Famiclone from 1996. It has trouble playing Mega Man 3. On the level select menu you can run it forever but in-game it crashes within a minute. After a crash you need to power off the unit in order to play again, if you only press reset it will crash almost instantly. I also tried Star Tropics which has very similar behaviour. Mega Man 4 wouldn't even get past the Capcom intro screen. I also have a multi cart with many games which won't even start at all, only a black screen. When playing compatible games (Mario 1-3, for example), it has no issues whatsoever.

What could be the cause of this incompatibility? Is it faulty somehow or are there certain NOACs that simply cannot play these games? My other Famiclone (older glob top from 1992) can play them just fine.
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Ben Boldt
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Re: Old Famiclone poor compatibility - what could be the cause?

Post by Ben Boldt »

There is nothing really in common with those games you mention. It sounds kind of like a power supply problem. Have you checked the internal 5V rail to make sure it is and remains 5 Volts? Especially when you get it into that crashed mode where reset doesn’t work. Be sure to monitor the voltage when it is doing that and as you press reset.

If you find that the 5V does drag down or get glitchy, that’s good news because it is probably easily fixable whatever would cause that. Let us know, we can go from there.
Famicloner
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Joined: Sat Jan 22, 2022 3:13 am

Re: Old Famiclone poor compatibility - what could be the cause?

Post by Famicloner »

Sorry, I was too excited and forgot to include more details.

I’ve monitored the 5V rail with a scope and it looks rock solid at all times, before and after crashing. I’ve replaced the internal power supply with a new heat sinked LM7805 with ceramic caps, 330 nF on the input and 100 nF on the output, as per its data sheet. I’ve tested using bigger capacitors (470-1000 uF) too but it made no difference. The external power brick is rated for 12V DC, 2,5A and is of very high quality. It works great with the other Famiclone.

It was crashing before I made these mods, too.
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Ben Boldt
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Location: Minnesota, USA

Re: Old Famiclone poor compatibility - what could be the cause?

Post by Ben Boldt »

Since you have a scope, you might want to look at each of the CPU-related signals in the cartridge connector with a crashy game running. Look for how low the lows are and how high the highs are. Look if there are any excessive rise or fall times. Check the delay between M2 and /ROMSEL. Just general signal quality stuff like that. It sounds like there must be something marginal where some carts/ROMs can tolerate it and others can’t.
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