Combating electrical noise inside an arcade machine .. What can I do?

leonk

Marked Wolf
Joined
Feb 24, 2011
Posts
211
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?
 

leonk

Marked Wolf
Joined
Feb 24, 2011
Posts
211
Update:

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?
 
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