AV modding a Famicom

[toploaderleo]

Alright so I've modded my famicom to use AV and I got the audio working fine, but the video isnt as easy. I tried following this schematic on http://jpx72.detailne.sk/modd_files/fc/avmod.htm but I dont know where to solder the resistors and compasitors. It looks like they solder to the 7805 but I donbt know where to put them exactly or how the video signal would get through then. Im still new to modding. I did try connecting them directly to pin 21 and I got video, but it looks pretty dark. Also I simply put the composite video directly onto pin 21 and I got the same result. so if someone could sent me a pic of this mod or tell me where to solder what. please help me

I jus tried connecting a a933 transistor to it and now it looks like the fami wont even turn on. I connected the emitter to the 300 resistor the base to pin 21 andthe collector to ground.

I jus measured pin 40 and Im still getting the +5 volts

[jb143]

They are connecting to pin 3 of the 7805 voltage regulator. That is the +5 in the schematic. They are also using pin 2 of the regulator for ground but you can use any ground point on the PCB. I'm having trouble finding a pinout of your transistor to really help you further. That video amplifier schematic almost seems too simple and I would think that the transistor you use would make a difference. I don't know...maybe it works just fine.

Also, if the Famicom stopped working then my guess is that you shorted out the regulator.

[toploaderleo]

SO what gets connected to pin 21? anything? and if the regulator was blown wouldnt I not get the +5 volts?

[jb143]

SO what gets connected to pin 21? anything? and if the regulator was blown wouldnt I not get the +5 volts?


Pin 21 goes to the base of your transistor.
The collector goes to ground.
The 300 Ohm resistor gets soldered to the emitter.
The other end of the 300 Ohm resistor goes to pin 3 of the regulator(+5).
One end of the 100 Ohm resistor also goes to the emitter of the transistor.
The other end of the 100 Ohm resistor goes to (positive) leg of the 220uF
The (negative) leg of the 220uF capacitor goes to the center terminal of an A/V plug
The outer terminal of the A/V plug has to tie back to ground on the Famicom PCB

*Usually* the pinout of a PNP transistor looking at the flat side with the legs pointing down is Emitter, Base, Collector. You'll probably want to make sure what yours is first though.

I'd recommend getting a protoboard to build this on. It's a pre-drilled blank PCB with copper pads on the bottom to solder to. You can get a nice clean and small board with it. Use wires to make the connections to the actual Famicom board. Radio Shack should still carry them.

If not, you can just solder the pins and wires directly together, just try to keep it clean and make sure nothing shorts...or will short when you put it back together.

Not keeping it clean and having wires going everywhere is just asking for a bad video signal ;)

Hope this helps.

[FABombjoy]

Those PNP transistors are ECB, not EBC.

The leftmost leg (looking at the label) goes to your 300ohm resistor (which goes to +5v)
The middle leg goes to ground
The rightmost to PPU pin 21

If you've already ran your +5 and ground from the regulator, that's fine. Otherwise use PPU pin 40 for +5 and 20 for GND.

If you're using the parts I sent you, it's a 2sa937, and the datasheet is available here:
http://pdf1.alldatasheet.com/datasheet-pdf/view/107607/ROHM/2SA937.html

[toploaderleo]

But before I was at least getting audio though. or if I placed the video cable to pin 21 Id atleast get a very dark picture. Now Im not getting anything at all. So could I have damadged the fami at all? how could I tell if I have?

[toploaderleo]

the 7805 does get pretty hot on the ground. Im still getting the +5 though. is it still good?

[toploaderleo]

Thank you all so much for your help, seriously I appreciate it alot. This is all so much clearer now & Im much more confident. I think I may have burned out the PNP transistor by hooking it up wrong the first time. Of course I cant even tell if the fami is fried. I hope it isnt :bawling:

[FABombjoy]

If you have a digital multimeter, testing the transistor is pretty easy:

http://www.kpsec.freeuk.com/components/tran.htm#testing



The base-emitter (BE) junction should behave like a diode and conduct one way only.
The base-collector (BC) junction should behave like a diode and conduct one way only.
The collector-emitter (CE) should not conduct either way.


As for the Famicom, it's possible that something (probably the PPU) was damaged. I would still double-check that your cart & games are clean and make sure it isn't something trivial like a stuck reset button. If you have +5v at the PPU then the regulator is fine.

[toploaderleo]

the PPU?! wouldnt that mean the whole Fami is dead? like im better off getting a new one?! :puppydogeyes:

[toploaderleo]

4408

I just unmodded the fami & hooked it up with an RF and it works!!! :love:

Of course by works I mean I'm getting video with no audio. BUT this mean I don't need to buy another one! and it means I can still mod it. Chances are the PNP transistor Im usin is blown same with the capacitor for the audio. because I cant think of any other reason they'd both not work. I'm gonna hook it all back up later and tell you all how its working ^-^

[FABombjoy]

The only way to know for sure involves using a logic probe or scope. I'm guessing the PPU since that's the neighborhood in which you're working, but it could be the CPU as well.

Before you declare it dead, be sure to check that:

-You didn't splash solder somewhere that it doesn't belong. Look under chips and cart connector as best as you can.
-Your carts & connector are clean
-Reset isn't stuck (Make sure CPU pin 3 isn't grounded)

Unfortunately, sometimes when you're new to modding, things go poof. It could be worse... when I was new to modding I deep-sixed a Neo Geo AES :)

Edit: Yay, it works!

[toploaderleo]

Thanks for the support. the NeoGeo thing makes me feel alot better ^-^

Im going to get a fuse on my way to class, then Im going to test the PNP, probably dead but I have a spare

I may have completely fried a master system, but at least I can find those in America '^-^

[toploaderleo]

It works fantastically. I discovered the main problem was I wasnt grounding the composite properly. But everything works, the Im so happy, and tired. thank you all so much for your help. I cannot express my gratitude.