Issues with RGB-Modded AV Famicom. *SOLVED*

[DaRabidDuckie]

Hi, all!

Been frequenting for a while but I've never posted. I'm hoping someone here can help me with an issue I'm having; I wasn't sure if this needed to go in here or someone else, so I apologize if it's in the wrong place.

I recently took the plunge and went all-in on RGB. SNES and Genesis are sexy in RGB (oh man, Gaiares...), and I purchased an AV Famicom to mod. Aside from an issue desoldering the PPU (which I replaced with an intact one from a broken NES at the store I work at) and a few traces on the Fami board that a friend had to repair because I got a bit happy with my desoldering iron, I had no issues installing the mod, or so I thought.

Basically, I can't get any kind of RGB output with a known-working SCART cable. My OSSC just does not see a signal from the thing, so I'm in need of some help. I did run a search through the past two years or so with no luck. I'm really hoping someone can steer me in the right direction.

If I try to run it over a SNES composite cable with the board installed I get a picture that looks like the normal game but it's white. Not a brightness-level white, like a monochrome white with no black in the picture. I'm told this was normal, so that gives me some hope. There was sound, but I didn't actually try playing the game when I was last testing at the shop. I just saw a very white version the title screen of Mega Man 3, heard music, and turned it off. I can check further if needed.

Unfortunately I'm not in a place where I can take a picture of how it looks, but If I take the PPU out of the RGB board and put it back into the Fami board it works just fine over composite.

-- Jumper J8 is open because I'd like to use TTL cables instead of 75ohm (so I can use the same cables as my 2-chip SNES)
-- J3 and J5 are properly shorted for Power and NTSC.
-- I'm using CS# as my video out, because again I'd like to use the same cables as my SNES. I did try outputting through V with no luck.
-- 3 and GND are jumped because I'd like to use the default palette.
-- I didn't cut the video trace on the bottom so I could switch between RGB and Composite as needed.
-- I did already check the voltage regulator just in case I had one of the faulty ones, it's fine.
-- I used a multimeter to check continuity of the ppu to the output pins, they checked out fine. Same with the wires from the rgb board to the video out pins on the Fami board. I do not have an oscilloscope. I'm used to checking continuity and basic voltage readings (I work on arcade sticks and USB devices a lot) but I don't know much about it past that.
-- If anyone needs to know, the stock CPU is 2A03H.

Here are pictures of the board and my wiring.

Thanks to all who took time to read this. Help is much appreciated!

edit: Pin 37 had a shaky solder joint at the header pins. A little solder got it fixed right up. Thanks so much for all your help!!!

[Syntax]

So you're running TTL sync to the OSSC?
Try 75ohm sync instead and see if it works.

[paulb_nl]

-- Jumper J8 is open because I'd like to use TTL cables instead of 75ohm (so I can use the same cables as my 2-chip SNES)

TTL cable so you are using a CSYNC cable for your SNES? Then you should connect CS# to pin 3 (CSYNC). You have connected it to composite video.

[DaRabidDuckie]

-- Jumper J8 is open because I'd like to use TTL cables instead of 75ohm (so I can use the same cables as my 2-chip SNES)

TTL cable so you are using a CSYNC cable for your SNES? Then you should connect CS# to pin 3 (CSYNC). You have connected it to composite video.

*facepalm* Right, because the Nintendo AV pinout is nearly identical between all the other NTSC consoles. I should have researched that pinout before posting. I feel dumb now. -_-

Anywho, I'll be able to test that later. Thanks a ton for the reply!

[DaRabidDuckie]

TTL cable so you are using a CSYNC cable for your SNES? Then you should connect CS# to pin 3 (CSYNC). You have connected it to composite video.

No dice.

pictures of 2nd round of troubleshooting

[paulb_nl]

Did you check continuity from CS# to the resistor in the SCART connector? Next I would solder a composite cable to the V pin of the board to check that its actually outputting something. Or connect Y to the multiout if you have a S-video cable.

[DaRabidDuckie]

Did you check continuity from CS# to the resistor in the SCART connector? Next I would solder a composite cable to the V pin of the board to check that its actually outputting something. Or connect Y to the multiout if you have a S-video cable.

CS# Pin to the resistor has continuity and outputs 330 ohms at the proper scart pin.

I think I've got a spare composite cable around somewhere. I'll try that and see what happens.

[DaRabidDuckie]

Next I would solder a composite cable to the V pin of the board to check that its actually outputting something. Or connect Y to the multiout if you have a S-video cable.

Soldered a component cable to V. Did you need me to try it on a TV or through my OSSC? I tried both composite and component inputs and got nothing.

For the heck of it I checked voltage on the board. Power is getting 5v and ppuv is getting 1.5v.

[Star1]

Have you also tried composite straight from ppuv? If I remember correctly this is composite from the ppu, just buffered. IF this works, but composite from v does not, at least you'll have narrowed down what the issue is.

[DaRabidDuckie]

Have you also tried composite straight from ppuv? If I remember correctly this is composite from the ppu, just buffered. IF this works, but composite from v does not, at least you'll have narrowed down what the issue is.

That didn't produce a picture either.

[paulb_nl]

So it seems the NESRGB board is not working at all. Do you still get a picture from the SNES composite cable? The output should be black and white. Try turning the NESRGB off and see if you get a color picture again with your SNES composite cable.

[DaRabidDuckie]

So it seems the NESRGB board is not working at all. Do you still get a picture from the SNES composite cable? The output should be black and white. Try turning the NESRGB off and see if you get a color picture again with your SNES composite cable.

With a snes composite cable and the mod enabled do I get a distorted black and white picture.

That's the Gemini Man stage in Mega Man 3, btw.


I disabled the mod and installed the ppu back into the fami board and got a normal picture.

Really starting to think I need to replace the board. >.>

[paulb_nl]

It shouldn't be distorted like that. Its probably the adapter board or NESRGB board. I would check continuity from all the PPU pins to all the adapter board pins ,NESRGB board pins and Famicom board pins. Also check for shorts.

BTW when you said ppuv is getting 1.5v I assume you didn't mean the PPU voltage?

[DaRabidDuckie]

It shouldn't be distorted like that. Its probably the adapter board or NESRGB board. I would check continuity from all the PPU pins to all the adapter board pins ,NESRGB board pins and Famicom board pins. Also check for shorts.

So I'm inferring from this that I'm supposed to be getting 1:1 continuity from each pin from the ppu installed in the NESRGB straight through to the Famicom board? If so, that might be the issue. The pins for EXT0-EXT3 don't seem to have a solid connection from the NESRGB to the adapter board. I could have sworn I checked these more thoroughly as I went through each layer. Hmm.

[paulb_nl]

I believe EXT0-EXT3 are only connected to the NESRGB board because they are connected to ground on the Famicom board.

[Star1]

Here are some tips Tim posted in another thread some time ago

"I don't know what's wrong exactly. If you have a multimeter handy, you can try these passive tests listed below.



This assumes you have a NESRGB with a PPU soldered onto it sitting in a socket on the NES motherboard? Disconnect the NES from the TV and power.

First test:
Set the multimeter to continuity mode. Test the continuity of the PPU signals between the PPU and the base of the NES motherboard. All pins connect straight through except 2-9 and 14-17. If a continuity is not present when it should be this indicates a bad solder joint. This is more common on the Famicom and top loading NES which requires an adapter board (and more solder joints).

Second test:
Remove the NESRGB from the motherboard (you can leave the PPU and wiring in place). Set the multimeter to resistance mode. Measure between 5V and ground. It should be greater that 1 k (kiloohm). If it is less can indicate a faulty video buffer amplifier on the NESRGB board. It shorts out the power rail when it fails.

Third test:
With the red (positive) probe on the ground and the black (negative) probe on the pin, measure in sequence the resistance between ground and each PPU pin 2-9, signals DP0-DP7. They should all measure similar to each other and is usually a value between 1 and 10 M (megaohms). One pin that measures significantly different to the others usually indicates a fault or bad connection on the NESRGB board. Measure again, but instead of measuring the resistance at PPU pins, measure at the pins protruding from the bottom of the NESRGB board. Signals DB0-DB7.

"

[DaRabidDuckie]

All pins connect straight through except 2-9 and 14-17.

That's exactly what I needed. Pin 37 had a shaky joint.

IT FREAKIN WORKS NOW!!!



Thank you all so much for your help!!!

[Star1]

I'm not even sure how that helped, but glad it did! Nesrgb is glorious!

[DaRabidDuckie]

I'm not even sure how that helped, but glad it did! Nesrgb is glorious!

I made a list earlier today of all the pins that didn't have continuity and compared it with the list you provided. I noticed that pin 37 on the adapter board output, which should have gotten continuity, had a loose joint that only got a proper connection when I pressed into it with my leads. One drop of solder in the right place fixed that right up. So yeah, the info you provided helped me figure that out! Thanks!


So to recap (and hopefully help someone in the future) here are the mistakes that I made:

* When setting the board to output TTL, I mistakenly connected CS# to pin 9 (composite) instead of Pin 3 (CSYNC). Huge thanks to paulb_nl for helping me figure that out one!
* I visually checked the solder joints in the adapter boards instead of properly testing them with a multimeter and missed one shaky pin that only connected when I pressed it in a certain angle.