Famicom | AV Mod

Famicom AV Mod | HELP!

Hi, new to the forum and was wondering if anyone would be able to help me out with the Famicom mod.

First of all I think that I have a "revision 7" Famicom, solder points from the mobo come from VIDEO, SOU, VCC and GND (These are clearly marked on the underside of the mobo as you can see below).




Instead of using RCA I'm trying to use a 2-pole mini jack and a 3.5 to Phono cable, like in this NES 2 mod.

I've built the amp on solder-less breadboard, here's the list of parts:

25V 220uF Capacitor
330 Ohm Resistor
110 Ohm Resistor
2N3906 PNP Transistor

The RF on the Famicom is untouched and still operational, sound works fine but I'm struggling to get any video...

For my amp i'm Working from this schematic:



Everything seems fine coming out of the famicom (tested with a multimeter), so I'm thinking that maybe the problem is the amp or the "VIDEO" solder point on the mobo, the 2-pole mini jack should be fine as it's just carrying a signal (Video/Audio shouldn't matter should it?).

Would really appreciate some help on this as all I want to do is play Rockman 2 and Castlevania III on my TV :nightmare:

I can post more pics of my famicom and also the breadboard if needed?

 

That circuit is attributed to me (but it's not "mine", it's Nintendo's). Are you sure you have the transistor wired correctly?



If so, try removing the 110 ohm resistor.



BTW, you can't test signals apart from low-frequency sine waves intended to power resistive loads with a multimeter. It'll just give you a RMS ("average DC equivalent") voltage and not even the right one because a multimeter isn't the correct load.

 

I see, thanks for the info its very much appreciated.

Is there a PNP in the list that you would recommend using more than the others, or are they all pretty much the same? It seems to differ from guide to guide, I'm in the UK but have an NTSC compatible TV.

 

I got a Famicom the other day which I also plan on AV modding so please post some pic of your board when its done.
Thanks

here's some links that might help you...
http://retrojunkie.net/modifications/nintendo-famicom-av/
http://www.famicomworld.com/forum/index.php?topic=4713.0

 

The transistor in this application doesn't matter too much since it's being used as a current buffer, not for actual signal amplification where its characteristics are important. You should be able to use any "small signal" PNP.

 

Did you lift pin 21 and get video from there?

 

Not a problem, BTW if you have a board like mine and you're taking sound from the "SOU" on the mobo then be aware that games which use the "EXTRA SOUND" option (like Castlevania III), will not work properly. To fix this you need to go to another point on the board, as seen in this pic (this isn't my famicom, it's an example pic but it's the same board):

Thanks, I'll try it out tonight and report back.

No i'm taking video from the "VIDEO" solder point on the mobo, (as in the example pic above).

 

lol not see that method before. Why are there so my different ways of doing this mod yet none of them have a good clear tutorial on how to mod them properly?

 

There's a few different revisions of the famicom so guides will vary I suppose, but I only became aware of the "MIXED SOUND" issue when I tried Castlevania III, it doesn't effect games that don't use the extra sound mode though.

Those links that were posted: the "Retro Junkie" guide isn't very clear (I spoke to the guy and he pretty much said that himself), also the thread/guide on "Famicom World" seems to "over complicate" things quite a lot...

I have a basic knowledge regarding electronics so I try to keep things simple if I can.

 

Ok that's fine but you will still have jailbars.

 

I thought that you get jailbars regardless?

 

Grabbing video from the solder points of the modo will produce some nasty jailbars,if you lift pin 21 and get video from there you will get little to no jailbars,granted your rf will be disabled.

 

Quick update, I have video : )

I think that one of the guides I was following may be wrong as it has the capacitor as:

I have "+ve" at "base" and "-ve" to "video out".

I've managed to capture the output, there does appear to be some "vertical banding"?, but I also get that with my N64 via (stock) s-video cable when using this capture device. It's not the best capture device in the world if I'm being honest but the image does appear to be a little dark as you can see:

[video=youtube_share;RpxoTcOEx_E]http://youtu.be/RpxoTcOEx_E[/video]

My knowledge of electronics is limited (so please excuse my ignorance) So I may have the amp wired up incorrectly, or might not have enough power, maybe changing the value of the resistor might work or include the 110k that I removed?

Just a couple of other things that might be relevant, I'm using a UK Atari Jaguar PSU (AC 230V to DC 9V - Output 9V DC, 1.2A, center negative) to power the Famicom and I'm also using Solid Core 0.6mm Hook Up Wire.

 

I'm confused about how you have it wired.

The PNP base should be connected to the PPU's video output, nothing else.
The PNP collector (same pin as NPN emitter) should be connected to GND, nothing else.
The PNP emitter (same pin as NPN collector) should be connected to 5 V through a ~300 ohm resistor. Then it should also connect to the positive lead of the 220+ uF capacitor. The negative capacitor lead should connect to the ~100 ohm (not ~100k) resistor.

You can wire the 100 ohm resistor before or after the capacitor, I think before is better, IIRC Nintendo put it after (as in the schematic).

 

So, wired up incorrectly and I'm using the wrong resistors (the store sent me the wrong type of resistors), a great start! lol

I had the "+ lead" from the capacitor and video out (PPU) at base and the "- lead" went to video out (TV).

The whole thing actually works without the 5v+ from the mobo so I guess that explains the dark image as well...

I'll have another look at it tomorrow and see what can be done.

 

Polarized capacitor isn't a good idea. I've always used non polarized cap (no + or - lead) so it can pass the AC signal (1v peak to peak typical for video output) while blocking any DC leakage.

 

Im about to mod my fami,if I get good results I will post it here.

 

Thanks, I'll take a look. What would be a good ceramic capacitor to use?

My neighbour has given me some of his old electronics stuff which contains a variety of ceramic disc capacitors.

Cool, always helpful to compare notes, BTW I came across this guide recently: looks interesting, he puts a cap on the PPU and the results look pretty good.

http://www.boards.ie/vbulletin/showthread.php?p=82882662

 

I highly doubt you'll find one that's 220 uF, most ceramic disc caps have very small values (less than 1 uF). There are nonpolarized electrolytic caps which are what you want I think.

 

wilykat: lecturing about subjects you don't understand isn't a good idea.

1) You almost have to use a polarized electrolytic capacitor, good luck finding a 220 uF ceramic... Besides, it makes no difference here.
2) All capacitors pass AC and block DC.