Problem with N64: No video but can hear audio works.

The console seems to play the game as I can hear the audio running. However it only outputs a black screen. Same for S-video and Composite. It will sometimes produce a flicker on screen on power on but not all the time.

I did a lot of testing. The obvious such as making sure the AV leads are good is checked.
I took it apart and it is one of the later revision with a MAV-NUS DAC/Encoder, so no RGB in this console. The DAC and encoder are integrated in a proprietary chip.

I checked continuity from the AV out to the encoder pins and there is no problem there, the path is good. I probed the composite output of the encoder, right on the chip pin, with an oscilloscope and can confirm there is no signal there.

I tried manually reflowing all the pins of the MAV-NUS and the RCP-NUS
Still no go.




I thought that maybe the encoder was bad. I checked it's clock line, data input lines and Sync line and there are signals going in. Can't if the signals are normal but all lines have a digital signal going in.

Thinking the problem could be the MAV-NUS DAC/Encoder chip I then unsoldered one from a scrap board I had and replaced it. ( Someone had drilled through that scrap board so I have no idea if it was good to begin with )

I really did good on my transplant I think. Used a hot air station and everything went great. No bent pin, messed pad or anything. New chip perfectly centered and all legs soldered well.
But then that did not change anything... Still have audio but no picture.

I wish i had a complete pinout of the NAV-MUS but there is only a partial one of the data inputs, it is needed for viletim's universal RGB mod.
At this point i am close to give up because I have no idea what to try.
I have some equipment like a hot air station and a scope but I am a still self learned amateur so hoping one of the senior repairmen here could give me a clue/hope.

 

I had a N64 with the exact same issue, try as I might, I was never able to get it working

 

I am almost tempted to get a VileTim N64 RGB kit, it completely replaces the MAV-NUS. It is possible a pin on the MAV-NUS chip controls the video output ( On or Off ), kind of like a Mute switch but for the picture. But since we do not have the pinout of that chip...

I am not a pro of the oscilloscope but I probed every single data lines + the clock lines + the Digital Sync + 3.3V + 5V and everything as far as I can see looks good. It is a complete mystery why it does not output any video.
But maybe VileTim's board would work since I apparently have all the signals needed.

 

Its possible that the chip just died internally somehow. What revision is the motherboard? By looking at the RCP date codes, it seems to be from very late 1999-early 2000.

 

I had one that was doing something similar and it turned out to be a corroded via. I ran a piece of kynar through it, connecting the components on both sides, and it started working. You may want to check over the board closely to see if there is any corrosion.

 

It is a NUS- CPU - 09 Year 2000 so yeah a late revision. I replaced the Dac/Encoder and I was hoping this would fix the issue but nothing changed. It is possible but statistically unlikely that I actually got another bad IC, as it was untested prior to the transplant. I guess the main coprocessor could be bad but as I said, I checked all the outputs with a scope and it seems to not be dead.

Visually at least the board looks great, cannot see any damage or corosion anywhere. Nothing looks tampered with either.
I know the encoder DOES NOT output video and that apparently all the data is being fed to it, so if a broken trace prevents it from working I guess it is from a !disable line or something alike. Do you remember what trace was damaged in your case?

 

I don't remember but I think i had to remove one of the heat sinks to see it. The rest of my board looked great too. Just had some corrosion in that one area for some reason. Took a while of looking over the board to see it.

 

Hmm... Bad board/RCP maybe or a hidden piece of corrosion? TBH, my N64 has two odd looking pins on the CPU facing the cartridge slot which looks likes it got corroded at some point but interestingly still works.

 

I've got a N64 here that won't output RGB although it's supposed to. Looks like the video encoder is shot, at least it does composite.

 

Maybe you should try pushing on the various chips on the console while it's on, maybe it really is a bad connection.

 

what does the rest of the mobo look like?

I've had some before, no boot..
but they all had corroded vias near the CPU between 91 and 120, sort of that area..

But the encoder is receiving data..

Is this how the n64 is broken down CPU -> RCP -> Encoder -> DAC

Could it be a shorted DAC?

Tried probing the encoder with the DAC removed..

I'm assuming that it's because it's close to the vents...........