Noisy Nintendo (But it's not the N64 that's at fault!!!

[rubber_jonnie]

I decided at the weekend to have a close look at the Intellivision, since I was still having display issues, in that the colour was off or missing when I first powered on but later on would return once the machine warmed up.

Having already seen some improvement from some earlier recapping, I decided that the most likely culprit was the PSU board since I hadn't recapped that at the time, and the caps were over 40 years old.

So I replaced all but one cap (The replacement for that is on order) and also swapped the 7805 for a Traco and I now get colour immediately I power on, which is great, but I also noticed a lot of interference.

I initially wondered if it was the Traco, but I found it was something else entirely, the PSU from my N64!!! Of course if the N64 PSU is plugged in, the PSU is always on, so simply unplugging it resolves the issue, but it's annoying nonetheless.

So I will see if I can find a way to resolve it. Serves me right for buying a cheaper PSU I guess, though the build quality is decent from a physical PoV.

I did fit a ferrite core to the mains lead, but no difference, and you can't fit ferrite cores to the power lead as it plugs in directly to the N64, so there is no lead.

[stephen_usher]

Stick a RIFA on the mains input side of the PSU? Bonus smoke in future as well as mains interference suppression. ;-)

[rubber_jonnie]

Stick a RIFA on the mains input side of the PSU? Bonus smoke in future as well as mains interference suppression. ;-)

Hahaha, yeah that would be a fantastic surprise for some retro bod in the future who isn't expecting a special magic smoke bonus 🤣

Not sure if it's mains noise or switching noise, but certainly something I could try.

[rubber_jonnie]

@stephen_usher I pulled it open and there is an X2 cap in the input, .1 uF. I do have a 47uF and another .1uF X2 cap in my box.

I do have a couple of unused Rifa polyester Y2 caps in my parts box, but one has already split in the packaging!!! Rubbish.

[rubber_jonnie]

Any guesses as to the location of the screw holding in the PCB?

IMG20250106145558.jpg

Yep, exactly where you think it is...

[alexh]

Under the hot glue holding the mains cable in place?

[rubber_jonnie]

Under the hot glue holding the mains cable in place?

Good guess, but under the great glob of silicone by the power outlet and the big glob of silicone next to the green cap.

IMG20250106164555.jpg

[Steve]

@rubber_jonnie could you explain your thinking / process here for education :) I've never dealt with this kind of issue before and I'm not familiar with X2 caps except they're always on mains input. I was also thinking that you could replace some of the cheap caps with good quality replacements, if you have any in stock.

[rubber_jonnie]

@rubber_jonnie could you explain your thinking / process here for education :) I've never dealt with this kind of issue before and I'm not familiar with X2 caps except they're always on mains input. I was also thinking that you could replace some of the cheap caps with good quality replacements, if you have any in stock.

Well the thinking was that I started to get interference on multiple machines, but it was most noticeable with the older Intellivision, probably because it's circuits are not well shielded. I initially wondered if it was my office fridge in the same room, but having seen this sort of interference before (I bought an OSSC and the cheapo PSU that came with it gave the same interference pattern) it occurred to me that it might be a more recent PSU, and the only one was for the N64. I unplugged it and the problem went away.

Next I added a ferrite block onto the mains cable, but it made no difference, and that is where I was up to the point when I posted.

The X2 caps are generally used for interference suppression, usually directly across neutral and live (RIFA caps are well know in this position) which is likely why @stephen_usher suggested I might need one across the mains input.

Now it does have one X2 capacitor installed but not directly across the mains, it's further into the circuit. I have an X2 cap spare that I will drop directly across the mains in to see if it helps at all. My worry is that is is switching noise from the cheap PSU and it won't make a difference.

I will test in a short while.

As for replacing the caps in it with better quality ones, I'm not sure that will help, but it is certainly something to consider. I could just buy a genuine PSU :)

Hope that makes some sense.

[rubber_jonnie]

OK, so I fitted another X2 cap directly across the mains and things are definitely improved. It's not perfect, and I will likely still just unplug the N64 when I'm not using it.

Maybe I'll just keep an eye open for a genuine part.