Famicom AC-Adapter and General Power F.A.Q.

Started by Xious, November 18, 2011, 06:54:54 pm

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January 18, 2012, 10:07:25 am #30 Last Edit: January 18, 2012, 12:25:33 pm by famifan
Quote from: fredJ on December 28, 2011, 12:44:56 pm
And yet another thing. What happens if the polarity is wrong? I usually test PSU polarity on my SFC console, it only starts with the correct polarity. So I know it is safe to try on. If I use the wrong polarity on the Famicom, will it break?

wrong polarity can't break it, i can guarantee that.

If you changed polarity the only thing is going to happen is that 7805 will heat a lot. But don't care, 7805 has internal shot circuit and thermal protection. I don't know the reason (is it shot circuiting or thermal overheating or both of them) but 7805 in that case will disable power output (by power i mean current).

So it is completely safe. 7805 will protect your famicom from wrong polarity.

if you don't beleive me, try to recreate this test case using a breadboard with 7805 and some other components. Also you should use multi-meter, it will indicate no current at 7805's output.

By the way, SFC/SNES and Sega 'Mega Drive'/Genesis use 7805 as power source too.

Also, 7805 has a wide voltage input range with absolute maximum at 24V. But it that case it will produce a lot of heat so thermal protection will disable output again.


Quote from: Xious on January 18, 2012, 05:08:18 amI don't however recall what the amperage rating of the PSOne PSU is, so this may not be acceptable.

The PSOne power supply outputs 2A so it's more than enough for the Twin Fami.


Quote from: famifan on January 18, 2012, 10:07:25 am
So it is completely safe. 7805 will protect your famicom from wrong polarity.

WRONG!!! It will burn out in most cases, but first, you will blow the fuse in your famicom!
It might survive a couple of seconds, depending on the strenght (amperage) of your PSU, but not long. Changing polarity will put electric current in every component of your Famicom where no current should ever be.
(just from my own experience with smoke and flames, I have burned a couple of 7805 with wrong polarity with just 12V !!!)


Early-model systems will destroy the 7805, or damage circuitry, as these models don't have a friendly fuse like the VCCi models. As I said before, it may survive a short while, but I have not tried a polarity reversal on a FC to check the effects over more than  second or two.  :bomb:


I have put in wrong polarity 9V DC in a couple of consoles, including Twin Famicom, with no problem, and for more than a second or two. How come it explodes for others? Is it an ampere or volt thing maybe?
Selling  Japanese games in Sweden since 2011 (as "japanspel").
blog: http://japanspel.blogspot.com

Da Bear

I have managed to put 5v to gnd without noticing it. The 7805 became hot and didn't output more then 1-2v, far less then required to power up the machine. But nothing blew up or burned (Yay!). When I found the short and corrected it the console worked again.
I'd say the safety-margins are pretty big, but there's a limit.


Maybe it's just me, I have blown at least four 7805s  :fire: :fire: :fire:! The plastic on them cracked and a gray disgusting smoke appeared! But I also destroyed countles USB drives just by plugging them into a computer!
It's magic ;D


Will this adapter work for a famicom... as i checked the topic the output is the the same but the input is not... i do not think that the input matters but still...
I am back everyone :)


The output amperage is a bit low (really should be around 850mA @ 10V), but it will probably work okay.


it will be okay only if it really outputs 700mA


Does anyone know why the Twin Fami PSU Amperage is so high?

It's interesting that the output is identical to the standalone Famicom and standalone Disc System - is this coincidence or intentional?


- Famicom: 850mA
- Famicom Disk System: 400mA

^ 850mA + 400mA = 1250mA

- Twin Famicom: 1250mA

Assuming that isn't a coincidence, it doesn't make sense to me as the Twin Fami only runs one unit at a time, that is either the cart or the disk - so it shouldn't need a full 1250mA. In theory, an 850mA PSU should run a Twin Fami just fine then?

I actually tested my theory and a Twin Fami that I have here does indeed run without any noticeable problems from a 7.5V 850mA PSU.

Any thoughts/opinions on this?


Typical "over-engineering" of the time, when things were built to last.


Hi all,

Bought an AV Famicom recently and was wondering about the PSU I'm currently using. After reading this thread, I still wonder if I'm OK...

I have an old wall wart (HP brand) with a rating of 9.5VDC 1.5A, which I've been using (it works). I also have a SNES adapter (US version), which has the correct rating of 10VDC 850mA, but the plug doesn't fit. Because the current rating on the HP adapter is so high, I decided to check the voltage and current under load (just loading the title screen of a normal cart) using a multimeter, first with the old HP adapter, then with the SNES one.

HP adapter: Famicom draws 350mA at 12.2V
SNES adapter: Famicom draws 350mA at 11.6V

Both voltage readings are a bit high -- shouldn't the AV Famicom operate at around 10V with the SNES adapter? And at 12.2V, should I ditch the HP adapter in favor of another one?

Current/voltage readings taken along the wire between the DC adapters and the Famicom DC input jack.
My outlets have an output of 125VAC, according to my digital multimeter.

Any advice would be appreciated. Thanks


Corn holo

Hey, does anyone know if you need a step down converter whan using a turbo grafx power cord?