Hey guys, first post here. I've been trying to AV mod another famicom after I accidentally blew up my first one... doh.
So I've done exactly the same thing, but with this one, it's gone all glitchy and I'm not sure why. I'm guessing PPU or SRAM, but I'm wondering if anyone else has any ideas first before I go desoldering and such. I should note that I saw a bit of corrosion on the U3 74LS139N, so I desoldered that and replaced it with the one from the first famicom, but it's doing the same thing. Although now I sometimes get a funky black screen too, along with the blue, red, purple and such.
https://photos.app.goo.gl/EibiHmC336mTJhvc8
This is what it's doing. There's a lot of jailbars on it too, which fade when I hold the reset button down. I also can't get any other games to play, just FF2.
I'd appreciate any help :) Thanks
what about pictures from your work and the scheme you used?
Post photos of the top and bottom of the Famicom board. Also, can you get past the file-select screen?
Here's what I've got. I know the perf board doesn't look great, but it's my first time trying to use it :)
Also, I replaced the transistor with the one from my old famicom, as I knew that one was working, but it does the same.
https://photos.app.goo.gl/8zBVSmqEcg4kQRAf7
It all seems to be working as intended though, no shorts.
https://photos.app.goo.gl/wCVmpTd93SEL3w7GA
Looks like I can go past the title screen, but it took a good 5 minutes to get the game to play.
Edit: This is the guide I used.
http://8bitplus.co.uk/projects/famicom-av-mod-nintendo/
Edit 2: I figure more info is better. I reset it after saving and it did save. But then it started doing this.
https://photos.app.goo.gl/pXaNTPJ87wVBpppH7
So your mod works, but the game glitches after some time in the game play right?
Is it a chance that you may be damaged the ram :-\
BTW you wrok looks like a total mess :crazy:
OK remove all that shit and start over , use this simple scheme by 80sFREAK and JPx72
It is the simplest one out here and very effective :)
Any PNP transistor will do the work, use the original one that you have from the famicom for example :)
There is no need to lift the pin 21 ,but is you are did this already then ok
Also very impotent - keep the wires as short as possible to minimize the noise
Haha, I know. I'm gonna remove the perf board, it's ugly. I'll give it a go, see what happens, thanks :)
As far as I know though, I haven't done anything to the ram though as I haven't even touched it.
Edit: Alright, so I've set up the new circuit, just temporary, but I'm still getting the same sort of glitches as you'd expect.
https://photos.app.goo.gl/Pca6D4bMQSF6XFE38
So you're thinking it's the ram that's the issue? I could swap it from my dead famicom if so, as that was working before I messed with it. I'm pretty sure it's just the cpu that's the issue on that.
https://photos.app.goo.gl/7Nz6DbPLoxN4wpNv7
Figured I'd tidy up a bit. The transister is straight onto pin 21 now. Can't get much shorter than that :D
If it worsens over time I think the problem is thermal. Anything getting hot to touch? Is the voltage regulator ok? You didn't short anything by accident?
Also do sound work? Audio is taken from cartridge connector pin 46 (or anything directly connected to that). It's already amplified and mixed with expansion audio there.
Although transistor goes straight to pin 21, other wires still looks long.
I don't want to complicate things for you, but this is the latest recommendation (https://forums.nesdev.com/viewtopic.php?f=9&t=18508&start=75#p237597):
(GND)
PPU.20 ----------------+---------------------------------+--------+
| | | | Ring
| | / (c) 2SA937 560pF --- +----O } Composite
| PPU.21 --|< PNP Ceramic --- } Video
| | ^ (e) 220uF | +----O }
--- 4.7-47uF | Electrolytic 110 | | Pin
--- Tantalum +----------|(---------/\/\/-------+--------+
|+ | +
| (+5V) 300 |
PPU.22 -------/\/\/----+
According to that thread it's basically the AV Famicom's circuit, plus a tantalum capacitor (anything from 4.7 to 47 µF) between +5V and the PPU's GND pin, minus a ferrite bead and minus a 560 pF capacitor. Tantalum needs to be soldered directly between PPU pin 20 and 22 to reduce the noise (Famicom only, on NES pin 22 isn't tied to +5V).
In your case you might just want to get it working first though.
Nothing seems hot I have to say. The CPU is a little warm and so is the 74LS139, but I think it's just the material, as it's a slightly glossy one from the other older famicom I have.
The sound is working fine yeah, no issues there. Maybe once I plug the second controller in with the microphone, but for now, all fine.
Yeah, I can probably shorten it a bit, but I'd rather just get it working first. I can worry about the jailbars later.
I think I might swap the sram over and see what happens.
Sigh. Well I swapped the U4 first and it seemed to get a bit more reliable at turning on, but with repeatable graphical glitches. So I replaced U1. Now I can't get the game to load. I hate these things lol. Guess I'll swap it back over lately, the heat is making me grumpy.
What kind of soldering too you are using? Is ti regular pen like one, or transformer pistol type ?
Because alternating current produced by transformer one might damaged the ICs ???
Just a normal pen type one on a station.
https://photos.app.goo.gl/N6WYpRuydWqwWdzX7
You need to wet that sponge! ;)
Lol, I don't use it anymore.
As FAMICOM_87 said, get that shitty AV mod out of there before it causes more problems, and you should also replace the RAM.
So I've removed both sram that were in and put in some sockets instead. It's still doing the same with any combination of the 4 I have.
Any ideas please? Lol
You only needed to swap the RAM used as VRAM I think.
Anyway, the VRAM was fine. Next you can try swapping the PPU.
Have you ruled out that your RCA connectors are okay? They look half plugged in, and, aside from that, sometimes poor quality cables cause distortion/signal loss. Try rotating them a bit and see if you get artifacts.