"Burn baby burn"...or Don't *face palm*

[Calypso]

Unlike the popular disco hit single, I would rather not have anything burning...
I will preface this post by saying TWO of my machines have had mods put on them, so I am inclined to think it is one of those two that is the culprit.

So like many a pachi-collectors, I often leave my machines on in the house when I am not playing. To my horror I walked into my "den" tonight and was met with the unpleasant aroma of what can only be described as a burning plastic smell. No smoke, it wasn't an odor that made it unbreathable or thick to where I thought there was an active fire, but noticeable.

Now my Popeye Pachislot tends to get a little internally warm (even when the coin mod mech is turned off) and its coin intake was a little warm to the touch (coin slot). I noticed this after shutting it off. My other modded machine is pachinko "non-clicking" Star Wars: BODV. But that is running fine, no heat and hard to believe it is the issue. Nothing inside of Popeye was unusually hot and BODV was not warm in back or front other than the coin slot a little warm. The LCD on popeye does get hot when I leave it on and it sits next to the coin slot Needless to say I turned everything off and it dissipated.

Anyone experience this before? I dont have much room between the back of my machines (chords) and the wall...should I increase ventilation?
What should I be looking for?
How best to troubleshoot with little to no tech knowledge.

Any advice or help would be appreciated. The only think I can think to do is turn them on one by one and keep an eye (or nose as it were ) on it to see who is making the smell.

But then what? Should I check for heat (like I did)?
Would I see black or burnt wiring?

Could it just be a machine that got too internally hot and it smelled or does it definitely mean a wire burning somewhere?