JAMMA board interfears with entire house!

[Hojo_Norem]

I just got a IREM Major Title JAMMA pcb (uses the M82 board, planning on converting it into a dual Major Title/R-Type 2).  As far as I can see the board itself is operating fine but after a minuet or so my TV loses sync.  All I need to do is swap from/to it's scart input and the picture stabilises again briefly.  Now you would think that it was the TV playing up but listen to this, as soon as the board is powered on (using my supergun I build in the projectlogs forum) the other TVs in my house exhibit a very strong interference pattern.  If I yank out the AV cable from my supergun the interference stops.

So the problems in my supergun you might say.  Possibly but the interference doesn't show when I connect up my MVS.  Could anybody spread some light on these issues?

PRE Post Edit:
I think I have discovered the cause of the first problem, the M82 board runs at a 55.somethingHz refresh.  That could be throwing off the sync on my tv which must be expecting 50Hz or 59.somethingorotherHz.

[ken_cinder]

Tried another power supply, or made sure your power supply was set for the proper voltage? The ONLY thing that the board would have in common with a TV in another room of the house, would be where it draws it's power.
Improper voltage selected, bad ground....... Out of my realm of knowledge, but it's not something I haven't seen before.

[viletim]

Now you would think that it was the TV playing up but listen to this, as soon as the board is powered on (using my supergun I build in the projectlogs forum) the other TVs in my house exhibit a very strong interference pattern.  If I yank out the AV cable from my supergun the interference stops.

Earth your antenna system?

[Hojo_Norem]

Thanks for the tips guys.  The voltage selection on the powersupply is correct so I think the problem can be narrowed down to grounding and/or EM interference.

I did some experementing and found that buy unplugging the RF feed into my room stops the interference in the other rooms.  Im thinking it could be some kind of funky ground loop problem as all my AV equipment is connected together via a SCART switcher.  One piece of equipment in my setup is a DVB reciver so theoretically the ground on that is connected to the ground on the game pcb via the scart switcher.

I have also found a workaround for the screen rolling issue, all I do is power on the pcb first and TV second.  The TV seems to lock on better and stays stable.

[ken_cinder]

Capacitor on the sync line to alleviate that problem? I had to put one on the sync line of my Jamma harness to make my PSOne LCD sync easier. Can't recall what value I used though.

[Hojo_Norem]

Well, I have done a little more experimenting and the conclusion I have come to is that the electrical design of my supergun is rubbish, or more accurately the SNES>JAMMA interface board I concocted.  When I designed the PCB for the interface I never thought of having a ground plane (or as much of one as possible on a 2 layer board).  Now I know of ground planes and what they do but it never occured to me to add one.  During the course of my investigations I saw that the interferance was present with my Neo-Geo MV1FS board but was hardly visible with my much smaller MV1B board.

I took a stab in the dark and disconnected the interface and left everything else intact and powered on....the interferance was barely noticable!

Now as a stopgap measure I have reduced the clockspeed of the AVR on the interface from 8MHz to 1MHz.  Thats made a big difference.  Anyway I'm planning on re-designing the interface (less ICs, smaller pcb, ground plane, etc) so I hope to avoid this problem in the future.

Capacitor on the sync line to alleviate that problem? I had to put one on the sync line of my Jamma harness to make my PSOne LCD sync easier. Can't recall what value I used though.

In this case its definately the tv.  If I leve the TV on a untuned channel, turn off, on and switch to the supergun, the TV acts if the signal is a 60Hz one and stretches the image accordingly, but the sync is rock solid.  If I leve the TV on a tuned channel and do the same, the TV displays as if its a 50Hz signal and acts finiky on the sync.  Im going to take the setup into work and try it on a few different TVs (incluging one or two of the bit 50" plasmas  )

[ken_cinder]

Wouldn't be the TV in that case. Standard res output from arcade PCBs differs ever so slightly from standard TV signal in sync that even the slightest variation, will make a finicky TV not want to sync.

I made my PSOne LCD sync by holding the ends of the sync line with my fingers before connecting, and connecting in similar fashion to how you've done it.
It would refuse to sync no matter what I did if the screen was cold started with the arcade PCB already powered, but if I fed the sync with the screen already "on" it took.

The capacitor corrected the need for doing anything in either situation, you might want to give it a try. My LCD TV on the other hand, just took the sync straight up, so it most certainly depends on how picky your display is.