Modding Famicom GPM [solved]

[Finfami]

So, at some point I will have to try modding my newer Famicom which has GPM board inside.

This seems to be the guide: http://jpx72.detailne.sk/modd_files/fc/avmod.htm

However, I have question regarding parts. I have 120R and 200R resistors and the guide expects 100R and 150R, how exact this has to be, can I use 120R in both locations or do I need to get correct ones from eBay etc ? Also there are mentions about 33uf resistor in the guide, I assume it reall means capacitor? If so, again, I have 47uf 16V capacitor, can it be used instead?

[HVC-Man]

µF means microfarad, thus capacitor.

By using parts out of spec, the end result of the mod will appear different from what is typically described. It may not be a whole lot though.

[Finfami]

OK, but the differences are not likely to cause any damages to components, they have some tolerance etc ?

[FAMICOM_87]

I used that mod instead the results  are satisfying https://playoffline.wordpress.com/mod/oldfcfba/
I suggest you not to disable RF functionality I already moded 2 consoles
here are my results : http://www.famicomworld.com/forum/index.php?topic=12059.0

[Finfami]

OK, I proceeded with the original mod, mentioned in the first message.

I get no sound and no video, the only thing which happens when I switch power on is that the constant hum heard from the TV speakers changes tone, that's it.

I was having some troubles soldering to pin 22, I couldn't get it to stick so I rebuilt the whole the on the backside of the board, carefully checking to connect to correct pins, B from transistor is connected via cable to pin 21 which is lifted and has no contact with motherboard. I have used 120R resistors and 47uf capacitor so as mentioned the parts are not exactly the same, 1uf ceramic caps I had.

I wonder if the transistor got damaged, or I made some soldering mistakes or it's simply because all parts are no correct. I tried to solder RCA connector to the negative pin of the 47uf cap to test video and then tried soldering it to pin 46 to test sound. No video, no audio, except that buzz / hum whatever.

Any suggestions?

[chowder]

If you could post some pictures, that would help people work out what's going on

[Finfami]

Yes, here are some pics. I actually removed all mods and redid it on the component side.

http://i6.aijaa.com/b/00401/13945753.jpg

http://i3.aijaa.com/b/00609/13945754.jpg

If I connect the Famicom to TV with audio pin, I instantly get some buzz from TV speakers and when powering on the hum changes tone. Clearly there's something wrong as my succesfully modded Fami does not do that.

EDIT: The resistor nearby PPU might have been damaged slightly during the soldering process?

EDIT2: During the difficulties of soldering to pin 22, could it be possible that I have created short circuit under the PPU or something, so should the PPU be removed? I have solder sucker so maybe I could do it altough I expect t to be tedious process.


EDIT3: Removed transistor and tried to test it with multimeter, never tested transistor before, but if I put to test mode I get readings when the prongs are like this:

http://aijaa.com/cLEUdp

Shows around 770. If I move negative lead to the third pin I don't get reading.


EDIT4: If I put negative on the first pin (counting from left of course) and positive to the third I get around 780.

[80sFREAK]

When you do soldering, use some flux, please. I very doubt, that you killed PPU(except ESD), but transistor.

[Finfami]

OK, I see that same model transistors are sold on eBay so maybe I'll try with new one.

Is the constant buzzing sound a clear indicator of failed transistor?

EDIT: Pressing reset switch also alters the tone so apparently it works and is not shorted etc.

[80sFREAK]

Test for the shortcuts is the first thing, which you have to do(especially with your soldering). Also check 5V on the pcb.

ANY PNP general low power silicon transistor will work.

[Finfami]

Measured power button contacts, around 5v when off, measure ppu pins, around 5v when on. Noticed that CPU does heat up if I leave the console on for a while, will check if PPU does the same.

EDIT: Also measured CPU and cartridge connector, all show 5V.

If the PPU is dead, where can it be bought at reasonable price? Found some on Aliexpress, but in lots, one seller was also claimed to sell fakes which is of course "great"..

EDIT2: I already ordered replacement transistor.

[80sFREAK]

Did you ordered flux?

[hvc01]

Remove everything and start again would be my only advice. Did you confirm if the board worked before you started working on it?

[Finfami]

Flux I didn't yet order.

Yes the Famicom worked fine and I was able to play with shitty image quality but perfect sound by hooking it first to VCR.

Yeah, I did restart once already.

[hvc01]

You should be able to get sound output...hookup an alligator clip to an centre pin of rca cable and pin 46 of cartridge connector and another alligator clip to ground on rc cable to emshield on famicom board and hook rca cable into tv. If you don't hear famicom music get another board.