nesdev.org

Hello! I recently picked up an AV Famicom and noticed that it was running quite hot, so I ordered this switch-mode voltage regulator replacement:

http://www.ezsbc.com/index.php/psu2-5.html

It works great while the system is operating, and now no heat is generated. Unfortunately, when the system is off I get a constant high pitch hum and video feedback on my CRT. It seems that while the system is off there is some stray current flowing to the AV port. Any idea how I can fix this? I tried removing the capacitors and other hardware from the original circuit as this new voltage regulator has all required circuitry built in, but it made no difference. I'd rather use this switching regulator than a regular 7805 just because of the heat issue, but the noise is very annoying. Thanks in advance!

I've had good results using OKI-78SR-5 in place of the 7805, in both the front loading NES and Famicom AV, without the symptom you're describing.

I've used that exact switching PSU replacement on all of my consoles, including a Famicom and an NES, so it's at least not an intrinsic problem with that model.

You can try adding various filter caps to the 5V output, though it wouldn't hurt to filter the input as well.