AV modded Famicom stopped displaying video.

Started by Desgranges, January 26, 2016, 09:23:03 am

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Desgranges

Hello Famicomworld,

I have a bit of a problem with my AV modded famicom. I modded it half a year ago to output composite video and faux stereo audio. Everything used to work splendidly, and I was happy.

Today, as I was going through some Ninja Ryuukenden, Rockman 2 and Dragon Quest 2, my famicom developed some strange visual problems, with colors getting darker and brighter in intervals of about a minute, a distinct fuzziness to the picture, and white horizontal lines that would develop into a full-on distorted picture that at one point cut out entirely for about 2 seconds. Most of the time, the picture would get back to normal after a short while. For example, it was displaying these problems on startup, but worked just fine after a few seconds of "warming up".

But now, when I turn on the Famicom, I get no picture at all - but sound works as usual. So the thing is definitely alive.

I'm thinking of two possibilities here: fried transistor in the video circuit (the one I picked off the board), or dead capacitors. I have a hard time believing the transistor just gives out like that, but I am most likely wrong on that.

Before I start tackling either of those possibilities, possibly looking in every corner but the one I need to direct my attention to, is there anyone who has had similar problems and knows what's wrong? I have disabled RF, so I cannot test it that way, unfortunately.

Thank you very much!

zmaster18

First, reflow all your solder points. Maybe it could be your caps. Were they brand new or taken from something else?

Desgranges

Thanks for the quick reply. My caps were all new, and I still have quite a lot of  the ones necessary. I'll try replacing them first.

zmaster18

Also, did you build the circuit on a separate board or did you just solder everything where the Q1 transistor is?

Maybe the original transistor you took from the board somehow died... But I'm not too sure about that. I really think this is the result of a connection gone bad.

Desgranges

I built the circuit "in mid-air" on the component side, which was quite a hassle . Separate board would be how I would do it if I were to mod a Famicom again.

I have a source for the exact type of Q1 transistor used in the Famicom, but before shotgunning my way through, throwing more new components into the circuit than I can shake a stick at, I was wondering if the problem was specific to a certain component type.

Thanks again. I'll desolder Q1 and test it with a multimeter (I don't quite remember how, but there was a quick and dirty way to do test transistors...) before recapping everything, which I wanted to do anyway.

zmaster18

Haha, I also use the term "mid-air" for Famicom AV mods that aren't on separate boards. :)

If you don't end up solving the problem, I recommend you start over with new parts and try it on a board.

Desgranges

Apparently my problem was rather simple, and I feel really stupid and relieved at the same time.

In my infinite wisdom, I socketed the Q1 transistor instead of soldering it into the circuit directly (to avoid damage mainly). It seems like the transistor sitting rather loosely in the socket was the source. I opened up the Famicom, got it running with no picture again, and out of sheer coincidence I happened to touch the transistor - then it worked again. Duh!

Thanks again for your time and patience.