Twin Famicom video issuue

Started by Fresh, August 28, 2011, 02:36:18 pm

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I apologize if there are any threads or resources addressing this. I've done some searching these last few days, but as I am really quite lost I figured the safest bet would be to ask about this first.

I've had a Twin Famicom for some months now, it hasn't had an issue. After playing for a while the other day, the game's graphics became garbled so I turned it off, and didn't think anything of it. I figured it was just a glitch.

At this time, when I boot it switched for disk system play, the screen looks like this:

And when I try to load a famicom cart, it looks like this:

(though this was 'playable')

At this time the console will not read famicom disks, I tried the game that I was playing when it corrupted and another to verify. However, due to all of the garbage on the screen, I can not read the error code. I'll deal with that when the time comes, but I figured I would mention it in case it is pertinent to the overall issue.

Anyways, rather than jumping to my own conclusions I felt it would be best to ask about this. If this is a hardware fault or something I've done, I just need to know :). Thanks folks.


If the game runs OK even though the graphics are garbage, your problem lies in the CHR / PPU data bus, which is usually caused by dirty contacts on the games or cartridge slot. If it even fails on disk mode then it becomes quite a bit more serious. It could be caused by cold solder joints, faulty VRAM, faulty address latch or even a bad PPU.

First try to rule out the simpler causes by taking the motherboard out, giving it a good clean and checking it for cold solder joints. Check the PPU traces to/from the cartridge slot with a multimeter, especially PPU D0 to D7. Otherwise start looking at the 2K VRAM, the LS373 and the 2C02 as possible suspects.


August 28, 2011, 04:40:21 pm #2 Last Edit: August 28, 2011, 04:46:52 pm by ericj
Good suggestions, 133MHz.

I had a similar thing happen with one of my FDS copiers awhile back. Turns out it was a faulty, cheap AC adapter that wasn't putting out enough amperage. Although the problem here is different, it may be worth testing it with a different AC adapter first.


Oh man that could be a whole number of things.  Does it work okay with carts?


August 28, 2011, 06:56:59 pm #4 Last Edit: August 28, 2011, 07:42:08 pm by Fresh
Nah, the carts will load but they are garbled.

Thanks for the suggestions guys, it gives me a good place to start. :)


I've started cleaning and it has helped a little bit. Enough that I can see some of the screen now, but it fluctuates. The error code is semi visible now though and I'm thinking it's reading error code 20.


literally that could be a loose connection on any number of chips.


Looks like it was, yeah. After checking the connections everything seems to be in working order now, and the disks will boot too. Cheers folks, thanks :).


Glad you got it working.  My first twin famicom arrived today and I'm really enjoying this system.  I already threw rgb and s-video into it....I'm still working on some stuff before I'll post the work