NES audio/video humming

[Jack McSlay]

recently my NES' A/V has been acting weird... After playing for a few minutes, I begin to hear a low-pitched humming noise and as horizontal bar that darkens a part of the screen, scrolls down and loops back to the top. After I turn off my NES, I can feel the A/V connectors warm if I had played for long enough.

[albino_vulpix]

What does your mod look like? Show us some photos if you can.

[Jack McSlay]

MOD? I've never modded any of my systems except for removing region lockouts

[l_oliveira]

I don't know the NES A/V but I know that the old NES used AC10V power supply (non polarized)
And I bet with you that the NES AV uses SNES style power supply (With polarity)

Assuming that the AV NES requires polarized 10v (like the JP and US SNES systems) the humming probably comes from the protection diode on the power entrance cutting half of the power. If so, the solution would be use a 10V polarized power supply.

But, this is a theory. I NEVER saw an A/V famicom or A/V NES so I don't know how it's power supply circuit works and what voltage it expects.

Have you changed the AC Adapter recently ?

[NFG]

Reasonably sure the North American NES2 uses the same AC power supply as the NES1.

[albino_vulpix]

MOD? I've never modded any of my systems except for removing region lockouts

I read that as NES2 for some reason wtf.

[Jack McSlay]

I don't know the NES A/V but I know that the old NES used AC10V power supply (non polarized)
And I bet with you that the NES AV uses SNES style power supply (With polarity)

what are you talking about? The old NES IS the NES with A/V out, and it uses a 9VAC power supply, and no, it started occurring before the last time I replaced it

[kendrick]

Please forgive Oliveira's assumptions, as the NES uses different AC adapters in other regions.

Per your original question? The A/V output on the original American NES comes out of the same shielded box that the RF output is generated from. There are a couple of coils in there, but I doubt that either of them are the source of the heat. But there is a big old electrolytic capacitor sitting there by the A/V ports whose job it is to smooth out the voltage spikes. I'm guessing that it's either failed, or is about to go, and that's where your heat problem is coming from. But without actually touching the unit for myself, it's hard to say.

If I were you, I'd operate the NES with the cover off and do some spot checking with one of those laser thermometers that cooks use to measure surface temperature. It's the only way to know for sure which component is actually failing.

[l_oliveira]

I apologize as I kind of messed up. Instead of A/V NES I should say NES2...

You can safely assume the big electrolytic capacitor is faulty, as Kendrick pointed out.
Poor voltage supply (caused by the faulty capacitor) may easily cause overcurrent on the LM7805 voltage regulator (the part attached to the heatsink close to the RF metalic box) due to lower voltage, causing it to overheat.

And that reflects on the output, causing humming noise and video distortion.

If it was a Famicom, replacing the AC adapter would fix the issue as both the capacitor and rectifier diodes are inside of the AC adapter, not the console. This is what Kendrick meant when he said that the adapters change by region.

[Jack McSlay]

Sounds logical, tho I will need to arrange some time to try it. Unfortunately I don't have a laser thermometer, so it seems it will be harder to determine the source of the problem by heat, but ill try

btw, how do I open the metal casing where the A/V circuits are kept? I've never figured it out

[l_oliveira]

For taking the top of the RF/power unit metalic case in the NES, you need to dessolder it completely from the mother board.
If your problem is just the capacitor(which seems to be your case), you can simply remove the bottom cover and have full access to the solder side of the FR/Power unit board. That should allow you to replace the big cap without much trouble.