Ground Loop Interference with NESRGB on Twin Famicom

[daskrabs]

I have an NESRGB installed on my Sharp Twin (AN-505BK). It works great, except I get some light scrolling wavy lines in the background over SCART RGB that I can only attribute to ground loop interference. Most noticeable on solid color screens. Odd thing is that when I plug in the RCA cables for either Audio or Video, the lines disappear and all is well. Composite is wired to the Video jack, and looks fine. I should mention I'm using the alternate wiring method with the replacement DIN instead of the mini-DIN. I've tried to re-wire the ground every way I can think of, but nothing helps. Does anyone else have this issue on their Twin, or know how to fix it?

[leonk]

can you post pictures?

Have you replaced the 7805? Have you removed / disabled the on-board amp? are you sure RGB wires aren't picking up some RF noise in the system? Which SCART cables are you using?

[daskrabs]

I'll post pics soon. Might be tough to photograph. I have not replaced the 7805 or disabled the on-board amp. Not sure why I would. RF interference is a possibility, but I'm not sure where it would be coming from. Maybe if there's a way to disable RF completely, I'd try that. I'm using a retro-console-accessories Neo Geo SCART cable.

[viletim]

daskrabs,

(In Australia the electrical safety potential is called EARTH and the chassis reference potential (of a given piece of equipment) is called GROUND so there is no confusion between the two. In North America everything is called just called ground which is confusing.)

There are no earth loops with video game consoles because no video game consoles are earthed. Your problem is something else. Perhaps you forgot to connect the outside edge of the connector to ground (easiest way is to solder the ground wire to a washer and put it through one of the mounting screws).

leonk,

The Famicom Twin power supply doesn't contain a voltage regulator IC. It's an entirely discrete design. Anyway, blindly replacing regulators isn't useful at all. They don't fail any more often than any other IC in a console.

[Voultar]

can you post pictures?

Have you replaced the 7805? Have you removed / disabled the on-board amp? are you sure RGB wires aren't picking up some RF noise in the system? Which SCART cables are you using?

The power circuit on the Twin Fami is comprised of a 2SB941 (power transistor) and a M5236L (secondary regulator).

[daskrabs]

daskrabs,
There are no earth loops with video game consoles because no video game consoles are earthed. Your problem is something else. Perhaps you forgot to connect the outside edge of the connector to ground (easiest way is to solder the ground wire to a washer and put it through one of the mounting screws).

I'll try that, thanks.

[leonk]

The Famicom Twin power supply doesn't contain a voltage regulator IC. It's an entirely discrete design. Anyway, blindly replacing regulators isn't useful at all. They don't fail any more often than any other IC in a console.

Hey, I wasn't suggesting he replace it. I was wondering IF he did; in case he used one of those switching replacements that seem to cause interference with the NESRGB.

[deltronik]

I recently acquired an NESRGB modded sharp twin famicom that exhibited the same scrolling waves interference pattern that you describe. Showed up on all outputs, especially visible in solid colors.

It ended up being my power adapter. I swapped the little wall wart I initially got for an adapter I found on ebay that resembles a laptop adapter. The new adapter cleared the video right up.

Good luck!

[daskrabs]

I recently acquired an NESRGB modded sharp twin famicom that exhibited the same scrolling waves interference pattern that you describe. Showed up on all outputs, especially visible in solid colors.

It ended up being my power adapter. I swapped the little wall wart I initially got for an adapter I found on ebay that resembles a laptop adapter. The new adapter cleared the video right up.

Good luck!

I'm glad you said that. I'm using a 3rd party PSU, but just bought a OEM one 30 minutes ago. I'll post when I get it.

[daskrabs]

That fixed it. Looks like if you're using an NESRGB you need a legit power supply and not a cheap third party one. Cheapo probably fine for stock units.

[pwnskar]

Hi! This is my first post!

I'd like to chime in that I too had the exact same problem as daskrabs and deltronik and that problem is almost completely gone after a new power supply.

However, I have another problem but I'm not sure if it's related. I'm not even sure it fits into this thread but here it goes.

When I have my twin plugged straight into my LCD TV through RGB SCART (standard NEOGEO deal) some games give me a dimmed down picture in certain screens. Most noticably in Kirby's Adventure. When I first power the console on, the image is excellent but after a few seconds into Kirby being drawn, the image gets very dimmed down. Resetting the console does nothing but if I turn it off for a while before I power it on again the image is nice for a couple of seconds.

The weird thing is that when I have the twin plugged in with the same SCART cable through an upscaler (GBS-8220 RGB/CGA/EGA/YUV to VGA with an LM1881N) the image is fine. Also, the composite image from the NESRGB seems to work fine and is never dimmed.

Another weird thing is that I just modded a PAL front loader which seems to be working excellently where my twin falls short. I have not been able to try Kirby's Adventure on the PAL front loader but Maniac Mansion works excellently where the twin does not. So I guess that rules out any error on my LCD's end.

Could my problem be that the NESRGB on my twin is not getting enough power? I've no advanced knowledge of how electronics work, I'm mostly just capable of following instructions, doing a decent soldering job and using a multi meter to check for continuity. The only thing I find differing between the two NESRGB boards are the version numbers (13 for the twin and 14 for the front loader, I think), jumpers, PPU's and the new voltage regulator on the PAL front loader.

Should I order a new voltage regulator from Tim and fit it in my twin? Is there any way to check if the board is getting enough power with my multi meter? Could the caps for RGB on the board be broken?

Any help would be appreciated!