Famicom AV mod with populated console5 pcb

Started by tombo72, January 26, 2020, 08:59:52 pm

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tombo72

Not sure if I am reinventing the wheel or not but I chose to go with the tiny PCB for a couple AV mods. It seems there is a lack of instructions for this mod specifically and I know it's not really rocket science but I plan to document the mod for the next guy. I also modeled a pcb holder to attach to the screw post in side the Famicom. After 3 revisions, I think it will work pretty well.







I have already soldered the a/v port and soldered most of the connections to the Famicom PCB. Need to lift pin 21 of the PPU and run a lead and then find a good VCC and ground.

tom

xIceMan

That's a very neat and clean solution actually. Good job!

Sadly I already modified my Famicom with this AV mod and I'm very satisfied with it:
http://www.jsrc.jp/denshi/fcav2.html

FAMICOM_87

January 27, 2020, 04:58:17 am #2 Last Edit: January 27, 2020, 05:04:58 am by FAMICOM_87
Cool idea , but it is recommended to be close to pin 21 as mach as possible.
Here is my idea based on scheme by "Krzy" :)

tombo72

Quote from: FAMICOM_87 on January 27, 2020, 04:58:17 amCool idea , but it is recommended to be close to pin 21 as mach as possible.


I didnt realize the pin 21 proximity. I can put the PCB on the other side so it is closer. Off to rev 4! Thanks for the info!

P

Latest research includes not lifting pin 21.

tombo72

Quote from: P on January 27, 2020, 08:39:21 amLatest research includes not lifting pin 21.

So just attach the lead to the leg in place?

xIceMan

Why would one leave pin 21 in place? I thought lifting it reduces noise/jailbars..or that's what's been said for years. What is your source?

FAMICOM_87


tombo72

Quote from: FAMICOM_87 on January 27, 2020, 09:24:33 amI do not lift pin 21 to use RF as well :)

Well, easy enough for me to try it without lifting. Hopefully some results this week if I can get some time set aside.

tombo72

Related Question: How much would gauge of the jumper wires to the CPU and PPU matter for this mod? xIcMans mod has me thinking about modeling a pcb holder that clamps to each side and hangs under the existing PCB. I would either drill small holes in the console5 pcb or just run jumpers over the side to the PPU and CPU leads on the bottom of the Famicom pcb. I would use a heavier gauge for the 5v and ground.

P

I'm not sure but I think adding jumpers might just worsen the jailbars.

Quote from: xIceMan on January 27, 2020, 09:06:13 amWhy would one leave pin 21 in place? I thought lifting it reduces noise/jailbars..or that's what's been said for years. What is your source?
If you lift pin 21 you sacrifice RF as Famicom_87 said. It has been done for years to reduce the noise but the AV-mod research has not stood still since then. I've explained my understanding of the current AV-mod situation here. Source is also there.

krzy

Lifting leg is great way to approach metal fatigue and ultimately break the leg.

Signal from this leg goes to the base of PNP transistor which is very close to the PPU, and then from it's emiter it is feed to the AV modulator. Signal (or noise) can't go from emiter back to the base, so no idea why someone could think that this improves the quality a lot. (*)

But if you're such videophile, you can just cut the trace connecting PPU pin 21 with the emiter. If you change your mind in future, you will be able to fix it with just one drop of solder. Lifting back the leg will make it break on 100%.



(*) In fact, if the modulator draws more/less current from the emitter, transistor will juice more/less current from base, but divided byty the transistor B coefficient (200..500), so the noise might have little impact.

FAMICOM_87

krzy is right! I do not know why everyone are so obsessed of lifting this pin 21 and put in danger the entire PPU! (BTW I managed to rescue some slimier chips by sawing  the IC body to reach the tiny metal pin remaining and solder to it with help from the flux one tiny wire to replace the broken legs, but it is very difficult, and fragile)   

xIceMan

Ah, thanks guys for the information and actually confirming that it is not recommended at all. Will undo it and grab the video from the VIDEO pad instead (as shown by krzy's picture, since I have the same Famicom PCB).

tombo72

Small update. PCB soldered in place. I did not lift pin 21 and pulled the jumper from the leg to the Console5 board. Ran the R,Y,W and ground leads from the new connector and pulled pins 1, 2 from the chip,  VCC and Ground. I have a pretty clear image but I havent any sound; just a hum and some interference on screen. Slight hint of jailbars too. I guess I didnt take a pic yet but I will post.

I need to troubleshoot the no sound issue then I will work on the feedback(?) line in the image.

tom