Technical and Repair Assistance

[Drakon]

hello people of famicom world.  I recently successfully added a rgb ppu from a playchoice arcade board to my AV famicom.  The picture looks brilliant.  Since the rgb is unamplified I'm building myself a small amp.  I'm just wondering....what part of the av famicom motherboard can I get +5v from?  It's model hvc-002

[133MHz]

Some revisions of the Famicom motherboard come with convenient solder pads marked VCC and GND. Otherwise you can steal +5V by piggybacking on any known logic chip you might find (like the 74LS139 - pin 8 is ground and pin 16 is Vcc)

[mog123]

I got a Famiclone that looks like a famicom, bought it for close to nothing. Well, on the downside, it doesn't have the video/audio block just the ribbon with goldpin slots. Anyway, I managed to track all the routes with a multimeter. And it has come down to 4 signals: Vcc, GND, Audio, Video. generally those blocks (in famiclones) have amps and lots of passive elements etc. I'm not good at designing those, does anyone have shots of those, or schematics?

Thanks

[133MHz]

This video amplifier should work for you:



As for the power block, just implement the LM7805 reference design with a protection diode and a 1000uF / 25V filter capacitor at the input.

[mog123]

K, thanks!

edit: could you tell me where did you get that schematic? maybe there's a good reference site I don;t know of?
Also, why no L/R channels?

[133MHz]

I drew it myself, based on Kefka's mod with a bit of modification on my part.
No separate audio channels because that leads to lack of enhanced cartridge sound. If you want to do a stereo mod you'll have to mix the CPU audio with the cartridge audio separately.

[mog123]

Hmm, I actually am not sure about the video pin.

Well, I Have a 7 pin connector. It has 3vcc pins (1 is connected with the switch), 1 Audio pin(it goes to the expansion ports 2 pin), 2 GND pins, and 1 (probably the video pin) pin that goes to a 74LS157 via some resistors.

Do you think it's the video or I'm making a mistake?

edit: I checked the last resistor that goes before the "mysterious pin" I thought is the video signal and it's 220 Ohm, just like in the famicom schematics:
http://nesdev.icequake.net/Ntd_8bit.jpg

So it must be it

Do you know a EU substitute for that transistor? alright, I found it BC547

Sorry for all these questions and edits:
I don't really know what you mean by a protection diode with a capacitor at input, You probably mean to straighten out the ac, cold you draw up a quick schematic of how it should look like? Wouldn't it be just better to use a DC adapter?

[133MHz]

Guys, please. No need to start a flamewar because of a 5 cent diode and a 25 cent capacitor.

Both the protection diode and the filter capacitor I mentioned are used in the original Famicom design. The diode protects the system from people using the wrong AC adapter with it or from a sudden failure of the AC adapter, by blocking the reverse flow of current. You're right in that it's not strictly needed, but it's good design practice to include one, makes for a sturdier product. The NES includes a whole bridge rectifier inside, which basically means that it'll work with AC or any polarity DC, combined with a big filter capacitor and a linear voltage regulator with a wide input voltage range results in a redneck-proof machine.

As for the filter capacitor, once again you're right that the AC adapter already contains a similar capacitor to smooth out the pulsing DC. However you must account for resistive losses through the long wire that connects the adapter with the system (especially at low voltages), electromagnetic interference that might be picked up by that long wire and things like power glitches caused by wiggling the plug. Poorly filtered power on a Famicom leads to hum bars in the video, buzzing in the audio and potentially computer crashes, so you could say that its power design was over-engineered a little to ensure top performance.

[mog123]

Now that's an answer that satisfies me. Thanks again! Also, I did the AV board already. If anyone wants to etch it, grab it here:

http://rapidshare.com/files/416343395/FamiAV.zip

[geekmiki]

Hi,

I'm back with my awful stripes problem on a Famulator... I didn't really get an answer last time and I've tried to solve it the simple way without success and it's driving me crazy.

Here's the setup:
-brand new Famulator (bought in Japan) in July
-CRT TV (works fine with Twin Famicom; Megadrive, NES)
-220V->100V step down transformer

I get these awful lines as shown on this picture: http://yfrog.com/2oimag0103cj

I've tried:
- changing the AV cables
- another AC adapter
- removing any source of interference around

Please help!!!!!

[crade]

Well, I can help with the last question.  Here is the NES to famicom pin map
http://nesdev.parodius.com/NES_ADAPTER.txt

I think you would want video output though..  I found it essential so that I could make sure the game was connecting properly before dumping the ROM.

Edit: hmm, I notice that pin 16 on that map is not mapped as it claims the famicom doesn't have the equivilent of the expansion port.  Maybe there is more to this story; not sure. Sorry.

[133MHz]

Why not try to "NTSC-ize" your PAL-EEC NES using spare parts from your Famicom? That would certainly be easier than trying to adapt a stock CopyNES to a Famicom.

Just replace the CPU, PPU and crystal oscillator with their Famicom counterparts and you should be good to go.

[kyuusaku]

This video amplifier should work for you:

This is not an ideal circuit, video should only be AC coupled on the output (here it is not even), and definitely not on the input in order to minimize low frequency attenuation. In this circuit the coupling is necessary since the PPU sinks current, but it can be avoided by using another common-collector/voltage-follower amplifier. FC video quality is very forgiving because it's generated out of square waves and is very noisy in nature, but still if you can do better, why not? No need to be sloppy. I'm also not sure if it's properly biased for the PPU's level and this especially matters if the DC offset isn't removed... (well, depending on the monitor used the black level or even sync could be off.) Instead of the cap and NPN I would suggest just using a general purpose PNP (such as the 2N3906) and a circuit modeled after Nintendo's (as follows):

Connect the base directly to the video pin, pull up the emitter to 5V through a ~300 ohm resistor, tie the collector to GND. From there you tie a 220uF cap's positive lead directly to the emitter, and place a ~110R in series with the cap's negative lead to your circuit's output.

[133MHz]

Well since that was the original circuit published on this site, I haven't really bothered to improve on it even after taking a look at better approaches on Japanese web pages, because it works decently enough . I'm going to try out your suggestion when I get some free time.

[rcvalkyrie]

Hi,

Someone mentioned on the introduction thread to post my concerns at the technical repair thread... Not sure if this is the one but if you can help me I'd really appreciate it :] sorry if it look like I crashed onto a party or something.... And please bear with my not so very fluent english -_-;

Anyway, I bought a Sharp Twin Famicom last week at a Japanese surplus shop. The seller told me it was in good working condition, though I had no proof of it, as there was no adapter included, but it comes with not less than 10 cartridges, and I thought my brother would find a way about the adapter (he fixes all electrical stuff), and its around US $8 (converted), so I took the risk and bought it anyway.

And, well, as expected, the unit didn't work. We found the right adapter and all, but nothing happened. The led just... flicker, then off.

The guy from the introduction thread mentioned something about a 7805... I really don't know what it is, but I told my brother about it, and he said he had stockS of those (well he said he had lots of it). He needs to know where to solder it, so he needed some sort of schematics or service manual or something. I am unsure what the exact problem is though, but yeah, basically the unit won't turn on.

Since I'm having trouble explaining things, I took pictures. I opened the box so I can show you the board. I know you guys are familiar with this, so I hope you can help me with what to do about it, Make drawings on the picture or something... Anything that would help me explain to my brother... hehehe. He is willing to restore the famicom and make it work again... That is, if its still possible..



[ Please let me know if I messed up with the dismantling coz I dunno what I was doing there x) ]

I really hope you guys can help me with this. Thank you very much