Famicom AV Mod FUN!! ...... sorta ran into an issue

[Delorean428]

Hey all   

First post here, Hope you guys can help out.

Ok so.. I performed the AV mod on my CPU-02 and everything turned out well!  I used some of the kit provided by Cons.5 (not sure if I can say the company name, have to read the rules again   ). I used the Famicom Q1 transistor, but with a 300 ohm and 100 ohm resistor supplied from the kit (since I broke the A933 trans)..

I tried the stereo mod but i have to wait for 47k pots to come in the mail, instead of using 10k's just to try out... 

ANYWAY...   here's my problem... after having everything setup nicely, and ready to be sealed up in the case again... i thought "wait a sec.. let me add an LED light so it has a turn on light!"...... bad idea for the moment...  i totally forgot the pinout on the PPU.. and placed the legs of the LED on Pins #21 AND 22...

BIG MISTAKE....  the LED lit up, but when i took it off the PPU and thought "lemme make sure it lights up again: (i dont know why)....  nothing.. no LED light.. NO VIDEO.. NO SOUND... ZIP

So now i have to borrow my father's multimeter since i dont have my own, and check the CPU, PPU, and voltage reg..  I had even changed the 7805 and still nothing..

no flashing of the screen when it's turned on and off either.. 


Anybody have any idea as to what the problem is? No sound, no video... (so far before checking with multimeter)

If the CPU and PPU must be changed (since no sound or video).. then I'll just have to wait for the NES I just bought off ebay to be delivered and swap everything if it's working well.


Any input will be appreciated!!!   




Post Merge: June 04, 2014, 04:40:39 pm
Or would anybody know how I'm supposed to troubleshoot this sort of issue?

What kind of voltage/ohms?

[fredJ]

Well, it sounds like typical case of "frying PPU"...
Sometimes people report it worked again a while later after it got to "rest", although I'm not sure how that is possible.

If the CPU or PPU gets very warm quickly (too warm to touch), it is a sign it is fried.

[jpx72]

Lower voltage (lower than exactly 5V) can also mean something dead is draining voltage.

[Delorean428]

Thanks for the replies!

Hmm.. I think that's possible. I picked up a spare (and very clean) working NES to pull both PPU and CPU out of to try and see if they were the issue.

I did replace the 7805 with yet another brand new one (instead of from my Genesis lol), and certain things would start losing voltage from 3v and decreasing (i can't remember what I tested)..

So we'll see what the issue is soon enough once i swap the PPU/CPU.. at least now I have a test board once i get my IC sockets in it
Post Merge: June 13, 2014, 08:02:16 am


Ok so...  I swapped the Famicom PPU to an NES (front loader).. .nothing...  Swapped the CPU, still nothing.. So it's not the voltage regulator, not the PPU OR the CPU..  I'm pretty stumped.. I don't think it can be the SRAM

like said before, something definitely can be draining voltage (need to break out the meter again), but It's weird.. all i did was place the legs of an LED on the PPU pins 21 and 22 (idiot...)..  but how could that make the WHOLE system stop working..  there is no sound, no clicking sound either when the switch is turned on or off..  no video..   just nothing

If anybody has any input, please share. I will be checking the GameTechUS vids on youtube to see if i can find a similar issue. 

[fredJ]

maybe dumb question, but have you checked the fuse?
Otherwise, you could start replacing stuff... Maybe SRAM.

[Delorean428]

Not dumb at all. But you mean the voltage regulator? I've replaced it twice. One from a working Sega Genesis, and another brand new. Still nothing.

The CPU and PPU were replaced with a front loader NES set and still nothing, however the Famicom's CPU and PPU were placed into my NES front loader (now test board) and they work.. so i don't get the issue.

I have to see what's draining voltage still and haven't gotten around to it... I dont know how something so minimal could cause such an issue.

Next thing on my mind is to check the diodes in the bridge rectifier, and if that has proper voltage.. then maybe i somehow blew the transistor/capacitors for the video output??

to be continued....  ugh   

[80sFREAK]

How about replacing transistor in video circuit?

[Voultar]

Could be a failing/fouled diode in the bridge rectifier. (Power circuit that converts AC to DC voltage)


EDIT: Ah, I see you've already mentioned that. Buzzing the board with a multi-meter will quickly answer these questions.

[Delorean428]

I think tonight I'm going to have some time to fool around so I'll grab my multi meter and see what I can find.

I'm going to find myself some diodes as well just incase I'll need them in the FC.. Honestly, I can't remember seeing diodes in my CPU-02, or my recently acquired CPU-07... we'll see 

I wonder if anybody else ended up in the same scenario
Post Merge: June 19, 2014, 09:39:37 pm
It's the 1.5a fuse

Nothing else shows any mA on my meter except for the power socket and the point of the fuse closest to the socket (of course)


Post Merge: June 19, 2014, 09:41:35 pm
Will a 1.5a pico fuse work? Or any other 1.5a fuse for that matter?

[P]

I think any 1.5A fuse will work. You could even solder a glass tube fuse holder (if there's any room) to make it easier to replace fuses without soldering in the future

[Delorean428]

You know.. that's not a bad idea

[Voultar]

Glad you got it sorted out. I didn't even realize that this unit had a PICO fuse.

[Delorean428]

I'm waiting on a package of 1.5A pico fuses, so as soon as I get one installed I'll post pics to confirm the issue being solved.


Now.. if only I could possibly figure out a way to have RF AND A/V ports on an original Famicom without jailbars lol
Post Merge: June 26, 2014, 07:57:14 pm
So... I added a 1.5a Pico fuse to my FC and.....

BOOM works!!!



Don't mind my messy work bench and Turbografx lol

[jpx72]

You know, I once dismantled the whole famicom like you did only to find out my video cable was faulty. Sh*t happens

[L___E___T]

Glad you fixed it in the end - I would like to get another original Red 'N' White Famicom and AV mod it, but I'm convinced I'd end up breaking ti and not knowing the hell where I went wrong.