Famicom World

Family Computer => Technical & Repair Assistance => Topic started by: tombo72 on January 26, 2020, 08:59:52 pm

Title: Famicom AV mod with populated console5 pcb
Post by: tombo72 on January 26, 2020, 08:59:52 pm
..............
Title: Re: Famicom AV mod with populated console5 pcb
Post by: xIceMan on January 27, 2020, 01:00:58 am
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
Title: Re: Famicom AV mod with populated console5 pcb
Post by: FAMICOM_87 on January 27, 2020, 04:58:17 am
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" :)
Title: Re: Famicom AV mod with populated console5 pcb
Post by: P on January 27, 2020, 08:39:21 am
Latest research includes not lifting pin 21.
Title: Re: Famicom AV mod with populated console5 pcb
Post by: xIceMan on January 27, 2020, 09:06:13 am
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?
Title: Re: Famicom AV mod with populated console5 pcb
Post by: FAMICOM_87 on January 27, 2020, 09:24:33 am
I do not lift pin 21 to use RF as well :)
Title: Re: Famicom AV mod with populated console5 pcb
Post by: P on January 27, 2020, 03:27:25 pm
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 (https://www.famicomworld.com/forum/index.php?topic=4788.msg185819#msg185819). Source is also there.
Title: Re: Famicom AV mod with populated console5 pcb
Post by: krzy on January 28, 2020, 01:09:26 pm
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%.

(https://obrazki.elektroda.pl/2647999200_1580245753.png)

(*) 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.
Title: Re: Famicom AV mod with populated console5 pcb
Post by: FAMICOM_87 on January 28, 2020, 04:35:08 pm
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)   
Title: Re: Famicom AV mod with populated console5 pcb
Post by: xIceMan on January 29, 2020, 12:31:12 am
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).