No sound through rf

[roost]

Hello,

New to the forum, but have been looking around recently since I acquired my first Famicom about a year ago.  I just received my second and I am having an issue with it.  I looked through the forum, but didn't find a solution, so I thought I would post and see if anyone could help me out or point me to a thread I may have missed.

I plug this second famicom in the same way I do the first one I have that works fine with rf.  This one shows video just as it should, but there is no audio.  I tried both channels and didn't hear anything either way.  I also unplugged the player 2 controller and still didn't hear anything.  Any ideas?  I could mod for AV, but I would rather keep it as it is.  I don't mind using rf and would just like it to function as it was made to, for now.  I've attached pictures of the board, in case that helps.  This is a HVC-CPU-05 board that was in a smooth bottom case with serial # H1826882 and round button controllers.  I assume it was one sent in for repair and the board and controllers were replaced.

Thanks in advance...

[famiac]

Audio comes from cpu pins 1 and 2. Try using a multimeter to check for output on those pins. If there's a signal, then there's probably a dead capacitor or transistor somewhere in the audio path.

[roost]

Thanks for the response.

I'm not an expert at this, but I checked voltage by placing one of my multimeter leads on VCC and placing the other one on different areas. When I check with ground, I get 5V, and when I check with video and sound, I get ~2.5V.  This is on both my working and non-working Famicoms.  On the working Famicom, I check pins 1 and 2 on the CPU as you said and I get 5V.  On the non-working Famicom, pins 1 and 2 only give me ~60mV.  Does this mean I have an issue between the cartridge connector and the CPU somewhere?  Or am I not checking correctly?

Thanks

[famiac]

Not sure i understand your reply. Did you measure 2.5V or 60mV?
This is the cpu pinout
https://wiki.nesdev.com/w/index.php/CPU_pin_out_and_signal_description

Insert a game into the famicom and load a level with music. Check pins 1 and 2 of the cpu with a multimeter and compare with your working famicom

[Great Hierophant]

On the underside of your board, near the expansion port connector, there is an orange mark.  Could that be damage to those traces which the mark covers?  Test the ends of those traces for continuity with your multimeter set to continuity mode.

You can tap line-level audio from the expansion port.  Get a cable and connect ground to pin 1 and signal to pin 2.  Alternatively there is a solder pad labeled SOU, you can solder a wire to it and a grounded pin near it (underneath the S in SOU) and look for audio there. 

[roost]

Sorry about the delay.  I hadn't gotten a chance to revisit this, yet. 

I checked the orange mark.  It was something that I could pick off pretty easily and I didn't see any damage underneath it. 

I didn't think about checking the expansion port.  I got a hold of a Hori S.D. Station.  When I plugged that into the expansion port and used some headphones, I did get audio.  I'm guessing there is a bad capacitor on the somewhere on the RF Modulator/Power Supply board.  I'll probably replace them one at a time whenever I get a chance.  At least I know I can get sound out of it now.

Thanks for all the help!

[80sFREAK]

Check ribbon cable.