Dead Famicom due to wrong polarity?

[Nanoka]

Last week I got an AV-modded Famicom, played with it for a few hours on the first day, powered on and off several times swapping carts. Next day I played with one cart only for about 1 hour.

Few days later, today, I tried turning it on again but nothing happened. I checked cables tried other AV cables but no signal. Cable works on another console... (tried multiple TVs to be sure.)

Apparently seller had a center positive adapter... it's 12V DC 1.5A.

How did it work for so long without problems with the reversed polarity?
Is it possible it's fine and I can try using another adapter with center negative polarity? (I have confirmed the adapter did not work with another device)
I can attach a picture from the insides if needed.

[Skawo]

Open it up and show photos of the power board - it's possible they switched the polarity internally.
Even if so 12V is also too high - should be 9V


In any case, the voltage regulator probably went toast.

[Nanoka]

I don't have the means to repair this myself but any information I can pass to the technician is appreciated.

[Pikkon]

I would check the fuse first,it could be blown.

[Skawo]

Doesn't appear it has been modified to accept different polarity.
Maybe the power adapter itself was?

Could be the fuse, could be the power regulator. Could check whether the regulator gets hot very quickly when the system is turned on.
Could also be the AV mod itself - since the system doesn't have a power LED, it could be turning on, but the video isn't getting through.

[Nanoka]

So today the technician told me it was the fuse, the console is running games but there is no video, only audio from both RF and the AV mod (the RF trace was cut but audio is fine). Also the CPU is getting very hot apparently and he suspects there's something wrong with the signal amplifier.

[Nanoka]

Update: The Famicom is back and seems to be working fine except I see two static lines scrolling on screen.
This is less visible on CRT but I can still see it.

I got a new 9V DC 1A adapter and I'm suspecting it could be the culprit, the only others I have in hand are 12V and I'm afraid of even trying them after what happened before...

Here is a video: https://youtu.be/YukJmINeWnU

Attached a picture with the new AV mod.

[Skawo]

That does indeed look like some kind of PSU interference.

[Nanoka]

Since the RF has been restored, today I taped together a RF cable and plugging it to the TV seems to have cleared that interference on the AV but looks like it only works if the cables are connected to the same TV as the interference still looks the same if I plug the AV to my capture device regardless of the the RF cable connection.

Could that have anything to do with it or would it still possibly be caused by the power adapter? I ordered a new one anyway.

[Skawo]

Generally it is unwise to leave the RF functional with an AV mod in place. It degrades the video quality a little bit.

As for the interference pattern, perhaps the additional cable is giving it extra grounding that makes it go away.

It is indeed likely to be the the power adapter. I've had an issue just like that once.
You could also try getting some of those snap-on ferrite cores and seeing if putting them on the video cable makes a difference.

[Nanoka]

Switched power adapter it still looks the same. Added one or two ferrite cores to the video cable and it made no difference.

Would this go away if I cut the RF trace again?

Edit: Plugging only the video cable produces more interference.

[Skawo]

Hmm :/
Where is the trace that was cut to disable the RF?

[Nanoka]

I guess it was from the PPU pin 21, which wouldn't apply for the current mod.

Splitting the video signal with a Y cable increases the interference even further. The pattern is still the same it just becomes even more noisy. The more I mess with cables the more it looks like something to do with grounding.

Here is a video with what happens when I touch a wire from the RF output ground to the ground on the tip of the video cable connected to my capture device input:
https://youtu.be/-qgm8lT6Zfc

Only works at the very end of the cable. I tried wiring to the middle point with an extension but seems to have no effect.