Drop-in Famicom RF box replacement with onboard regulator + AV out schematic review

[domendevin04]

Hi everyone,

New face here, I’ve been working on a drop-in replacement PCB for the original Famicom RF box on the back of my cpu-07 revision board for a while now and am at the point where I feel comfortable showing it to a forum. The goal is to keep the motherboard untouched and plug into the existing ribbon cable, while replacing the RF output with clean composite video and mono audio. The board also includes a buck regulator (LM2596) to generate 5 V.

Here’s my current schematic (attached below). I’ve colour-coded the nets for readability and split the PSU and AV sections.

Power section:

AC input → bridge rectifier → fuse + protection diode.

LM2596 fixed 5 V regulator with SS34 diode, inductor, bulk and bypass caps.

Decoupling on the regulated rail: 0.1 µF + 10 µF + 47 µF after a ferrite bead.

Video buffer:

NPN transistor (emitter follower, 2N3904 type).

Base bias: 1 k resistor in, 100 k to ground.

Collector fed from 5 V_AV via 1 k resistor.

Emitter → 220 µF coupling cap → 75 Ω series resistor at the jack.

Optional 220 pF shunt cap at the jack.

Audio:

Input → 1 µF MLCC coupling cap → 100 Ω series resistor → audio jack.

Output:

Combined 3.5 mm TRS jack (tip = audio, ring = video, sleeve = ground), designed for TRS → RCA splitters.

Questions:

Does this schematic look electrically sound as a drop-in replacement for the RF mod box?

Are there any obvious mistakes with component values or placement (especially the video buffer)?

Any improvements you’d recommend before I move to PCB layout?

What I have:

schem snip.PNG

pcb snip.PNG

Thanks in advance! — I want to make sure I don't have any stupid slip ups before I do anything like order boards or components.