Combating electrical noise inside an arcade machine .. What

[leonk]

Background:

Got a New Astro Cab that has been running MAME (via ArcadeVGA/JPAC). I recently acquired a Naomi 2 setup for more modern games. I decided to get both of them installed at the same time, and use 2 switchers to select what system should run (DB25 2-way switch for controls, and DB15 2-way switch for video)

I purchased harness and finger board from JAMMA boards, and wired it all up. For the most part it works GREAT! I can now select what system I want to control/display, and I managed to actually get a full MAME setup + Naomi 2 setup (2 power supplies, and all!) inside a NAC!

To accomplish this I made the following adapters:

- 2 * JAMMA->DB25/DB15 (between Naomi and switchers + between JPAC and switchers)
- 1 JAMMA edge->DB25/DB15 (between NAC harness and switchers)

I got only 1 small problem, and I'm not sure what I can do, and figured maybe someone can point me in the right direction:

When I have: JPAC->NAC JAMMA harness, the video is nice and clean.

When I have :

JPAC->JAMMA Harness->DB15 -> high quality shielded 6' VGA cable -> DB15 -> JAMMA fingerboard-> NAC JAMMA harness

The video is nice, but in Windows (in 480i) I can almost see a faint shadow around the mouse cursor which suggests noise being pickup somewhere. When playing games, one doesn't see/know it's there .. but it kills me that I'm picking up noise somewhere, and not sure where!

I know the JPAC amplifies the signal, so it should be nice and clean. I made the wire harness/fingerboard wires as short as possible (~2") before they enter the DB15 on both . Inside the DB15, each has R,G,B,composite sync and GND is connected to GND + GND for R,G,B and grounded to actual plug.

Any other suggestions? Has anyone tried something similar?

[viletim]

This is not noise, it's signal reflection. This happens because the characteristic impedance of your source (your JPAC), transmission line (cable), and load (monitor) are not matched - not even close. It is the nature of arcade video signals. The effect you see will get worse the longer your cable is. The simplest solution is to keep the cable length short. No need for shielded cable or coax. Just make it short.

[leonk]

I purchased a gender changer and used it to connect the 2 harnesses directly. Shockingly, the signal is perfectly clean! I think I know what's going on here (correct me if I'm wrong - hope this helps someone in the future)

Signal coming out of pcbs or jpac is at arcade specs (2.2 Vp-p, 2.2k ohm input impedance) VGA on the other hand has input impedance of 75 ohm! So a VGA cable can't be used as a connector between standard CGA monitor and pcb/jpac! It will cause ghosting.

Sounds right?

***OR***

The VGA cable adds 6 feet of cabling that causes the ghosting. Doesn't matter if it's highest quality VGA cable, CAT6 or shoe string, the extra length of cable is the root cause.

[Fudoh]

I doubt that you'd have any problems when using a 1 ft. VGA cable.

[viletim]

The VGA cable adds 6 feet of cabling that causes the ghosting. Doesn't matter if it's highest quality VGA cable, CAT6 or shoe string, the extra length of cable is the root cause.

This one.

Arcade video is a bit like a PC parallel port printer in this respect. Cheap and simple, but limited range. A 75 ohm video system more like a network printer. The range is much longer, but only if you use the correct type of cable!

Arcade video was intended to be the most cheap and simple method of connecting a video signal which is generated by a bunch of TTL logic chips to a dedicated monitor which will never be more than a meter away from the source.

[leonk]

Thanks.. that explains a lot.

What about controls? Currently I have: JAMMA harness -> 6' DB25 cable -> switcher -> 6' DB25 cable -> Cab harness -> buttons/joysticks

I haven't noticed any lag/issues thus far.