Famicom av mod instructions?

[bayoubilly]

I did the mod using kyuusaku's schematic and I get the "jail bars"   they are really bad especially on a  blue background. they look just as bad as the nes2 vertical lines.

[petik1]

Which board do you have? If you have the one with the clearly labeled VCC GND SOU and VIDEO, then this thread may help http://www.famicomworld.com/forum/index.php?topic=3924.15

[jpx72]

I've found another interesting schematics, on the Polish forum by a member dic-sc7

http://www.forum.emunes.pl/index.php?topic=3381.0

(the FC means ferrit-circle)

EDIT: According to the author, this schematics is his own AV-Mod design.

[zmaster18]

I used your schematic jpx72, and I'm not getting any video signal. Sound works perfectly though. Could you help me out?

Some things that could be the problem:
-I used Q1 on the board as my transistor
-I connected a 10k resistor and 100k resistor together because I didn't have a 110k resistor.

I know the solder connections are solid, as I used a multimeter and got current going through every connection.

I can include a picture of the circuit if necesary.

[2A03]

I used Q1 on the board as my transistor

I think that's your problem. Did you actually desolder it from the board, or did you just solder your connections to it without removing it? If you didn't remove it, you should cut the traces connected to the transistor pins.

[jpx72]

Hmm no, I'm using the on-board transistor as well without any cuting or desoldering. What type of famicom do you have (pcb model number)? And how do you connected those resistors? Because if you connect them parallel, the ohmage is not calculated together... BUT there is no 110k resistor! It's 110 ohm (not 110000)!

[zmaster18]

ah, it's 110 ohm! I'll go check my parts to see if I have  it. I'm a beginer with electronics, so what I did with the resistors made sense in my head!!

As for the transistor, I noticed that the video signal was already connected because its trace leads to the video pin on the PPU.

Well, I'm gonna give this another go. Thanks for the advice!

[jpx72]

If you cannot find it, try it without it.

[zmaster18]

Alright, I replaced the resistors and now have video. The colours are kinda off - Mario's sleeves are green instead of brown. I tried different resistors ranging from 500 - 2200 ohms, used a different capacitor, and still no difference. The only thing I haven't changed is the ceramic disk capacitor which is 560pf.

[jpx72]

Hmm at least some success.. I know now, that my schematics isn't so universal, and I have seen so many designs lately... What PCB do you have (the white number/code on the components side)? Only thing I can advise you now is to try your own transistor instead of the built-in one, and take the video signal directly from pin 21 of PPU, and also the resistor of choice - try using the lowest range (or lower, like 300). But don't cut/desolder anything on the famicom board, it can be done without it, be patient.
Maybe using the other schematics (not reffering to anything in particular) with NPN transistor is more universal. OR  - one member here is onto something lately, trying to bring the AV mod to perfection, so maybe you can wait for a little while to see what he will come out with.

[zmaster18]

So it's the transistor? I only have two other ones: C1815 and S9015. I remember reading somewhere about the C1815 being used.

[jpx72]

The S9015 is PNP (if I am reading the datasheets right) . C1815 is NPN. So for my schematics you will need the S9015.

[kyuusaku]

I've found another interesting schematics, on the Polish forum by a member dic-sc7

This circuit is pretty bad too, it seems anyone will just post anything...

TO EVERYONE, HERE IS THE BOTTOM LINE: The video output by the PPU is READY for connection to a TV. It is a *PERFECT* signal which doesn't need "cleaning". The only reason for a transistor is to buffer the signal and match impedances. When you use these crazy circuits which are clearly not designed by video engineers you do one or more of the following:

-create filters which reduce the horizontal resolution
-create filters which result in the loss of color information
-amplify the signal and brighten the image
-attenuate the signal and darken the image

"Jailbars" are caused by interference, probably on the chip's power rails. Using different exotic video amplifier circuits will not fix this issue.

(the FC means ferrit-circle)

It's not circle but CHOKE. A choke is an inductor to pass DC and block AC and it's not really desirable here.

[jpx72]

Thanks kyuusaku, can't argue with that, but:

-create filters which reduce the horizontal resolution
-create filters which result in the loss of color information
-amplify the signal and brighten the image
-attenuate the signal and darken the image

-this is what we're trying to do and as you can see we are not good at it. If you want to be of help, propose a schematics to built those. I think everyone involved would be really gratefull if you do that. Really. Please.

[zmaster18]

So all I need to do is wire it up with a transistor? Why haven't I seen this done before?