I posted this on KLOV too, have not had anyone with same experience, so will try on this side of the fence.

I have just acquired an original Space Invaders upright arcade game. All works great. But I noticed that when someone else is playing one of my EM pinballs, faint vertical lines appear on the SI monitor for a split second when a solenoid fires.

All the machines are in my basement on the same circuit. I tried one of these:
amazon.com link »

and it made no difference.

Even with just the SI and one PB switched on, the furthest one away (3 yards), it still has this affect.

I am wondering if this is damaging the monitor, because if not, I can live with it as its rare someone plays a PB when the SI is on.

But if it is, any thoughts on resolving?

Thanks.

So, I ran a long extension cable up to my living room and it fixes the issue - so seems its a "on the same circuit" thing rather than a "physical proximity" thing.

Someone on KLOV suggested I simply split the circuits in my basement.

"Simply" - for me that means calling an electrician as I'm not comfortable with that sort of voltage.

I already tried this
https://www.amazon.com/gp/product/B00DBAAJQ6/ref=oh_aui_detailpage_o04_s00
but made no difference - unless there's something out there that helps keep the power smooth from split second drops (which I assume is what's happening as the PB solenoids draw power) then I'm heading down the path of running multiple circuits to the basement.

Dave, thanks for the offer - just checked the ebay link and given the price, I'm happy to buy new.

Grounded..let me check tonight. The SI definitely is as I had to replace the plug. The EM's, I'm not so sure, some I know are as I replaced the bad cord, but even then, I only ground onto the metal of the transformer mount and the door.