Just recieved an AV-modded Famicom in the mail yesterday and it works fine and dandy. However there are some problems with some games.
Gradius 2 for example, which uses the VRC4 looks pretty glitched. Hitboxes are way off the sprites and even those behave very random. Also some powerups tend to be broken.
Lagrange Point however didn't show a lot of problems as far as I've played it. However the TV does not recieve the expansion sound channels, only the ones from the NES' pAPU.
One time I read a post here about Gradius 2 hacking into MMC3. Some one mentioned that the VRC mappers from Konami relied heavily on IRQ timings, I don't really know how it works. However since I use a PAL television I guess this is the reason for the problems. Is there a solution for this? People say that a VCR can solve that but there are also little devices you connect serial between the console and the TV called "Overlayers". What do you recommend?
This doesn't make any sense, the console is oblivious to your PAL (multi-system?) TV and couldn't switch to a PAL mode if it wanted to. In addition to being AV-modded, it must also be PAL-modded with a special timing generator/transcoder chip sold in Hong Kong. In those, the channel switch functions as a PAL50/PAL60 switch, so you might want to try that. If that isn't the case at all, post pictures.
Due to the dominance of United States-based companies in feature film and television production, many "PAL televisions" are multi-system: they can also display NTSC and PAL60 signals, possibly even in PAL/M (Brazil's variant of PAL60). If your TV is a CRT SDTV (not something with an upscaler), you can tell a 60 Hz signal from a 50 Hz signal by peeking at it out of the corner of your eye. The flicker on a 50 Hz signal will be stronger than on 60 Hz.
If you have an authentic NTSC console and authentic Game Paks, I don't see how sprite problems could occur. The lack of mapper sound in Lagrange Point points to the console not being wired for mapper sound, which in turn points to the possibility of having received something other than an authentic Famicom. Some games don't run on famiclones, especially those based on the NOAC chipset, due to slight differences in PPU fetch patterns. (An authentic MMC5-based Game Pak is a great test for accurate PPU fetch behavior.) There are a few possibilities:
- You have an authentic Famicom outputting an NTSC signal, and your TV is multi-system.
- You have an NTSC famiclone, and your TV is multi-system.
- You have a PAL famiclone with PAL NES timing (longer vblank, slower CPU).
- You have a PAL famiclone with the mostly-NTSC-compatible timing used in some PAL famiclones (longer vblank, same CPU speed as NTSC).
Even if you are using an authentic Famicom, if you're using a PowerPak or other copier, you might still see mapper implementation defects.
Konami games set the IRQ timeout (which is CPU cycle based) at the beginning of the vblank period. PAL NES has a longer vblank time, so it triggers much sooner than it would on an NTSC NES. So it will split scroll at the wrong time, bankswitch graphics at the wrong time, etc.
Tepples recommended using an NTSC NES, so there would be no glitches within the game.
The Famicom is an authentic NTSC one, that is out of the question. The TV itself is capable of NTSC mode, as I tested it out with a NTSC NES console. Sorry I didn't mention that before.
I've also tested different Famicom games (SMB, Dragon Quest2, Tetris, Dr. Mario) and all these worked great. Scaling of the screen and the speed was OK. The game behaved like the should. I'll try to make a video out of those games as soon as possible.
Open it up and take a picture of the pcb. It COULD be a hong kong famicom model. Those are 50 hz iirc.
Processor: RP2A03E
I didn't know there was a Hong Kong Famicom. But doing a quick Google search seems to turn it up in at least one place. I'd only seen the official HK NES, and their distinctive light grey carts.
I have a PAL Famiclone, one time I had a chance to test with expansion sound (Namco106) and it sounded pretty bad because of it being out of tune with the internal channels. So if that's the case, that actually would explain why the sound would be left unwired. Though I don't think Lagrange Point does much tone-wise with the internal channels, so that kinda sucks.
And regarding the "timing sensitive IRQs", that's because it uses CPU cycles for the IRQ timing, so yeah it'd be screwed on PAL mode. Unlike MMC3, which is more tied to the PPU's scanlines.
Well that is the NTSC chip, 2A07 is the PAL one. Weird. That's an older revision of the CPU too (E version, is it the original one?). A google for that turns up nessound.txt mentioning (2nd-hand) that the E version doesn't support the "looped noise", interestingly.
How about a picture of the RF board, bottom side and AV modification?
It has an av mod? In that case thats probably why the expansion sound wont work. The guy who installed the mod probably tapped the signal before it passed trough the cart where it gets mixed in.
That's a horrible mod, I'm surprised it works. From my experience you need a buffering amp.
Though you didn't post a pic of the RF/power board PCB, it's not a PAL modified FC since there would be more jumpers to the main PCB. Perhaps the IRQ trace to the connector is broken, but that wouldn't explain all of the symptoms.
So if this isn't the proper way to mod a Famicom, does anyone know where I can find a tutorial for? Famicomworld had one but the site is gone.
http://famicomworld.com/ still exists. You could try asking at their forum if someone here doesn't have a link to some sort of guide.
I wouldn't go to Famicomworld for any info... Besides, most of the amp circuits out there aren't designed properly for the job.
You can use any general purpose PNP transistor.
You should definitely remove the RF modulator if it's still present so it doesn't affect the mod.
For audio connect the positive leg of a 10uF capacitor to the cartridge connector pin 46, and the negative leg to your audio output. I'm not sure what the level is/if it also should be buffered but that's a better start.
Thank you for your replys. I'll post the outcome later on.