Isolation Transformer

[coliveira]

Hello all

I am under the impression that the isolation transformer should be wired before the monitor to protect it.  My isolation transformer appears to not only 'filter' the power to the monitor, but also the switched power and marquee.  It's a Mortal Kombat cabinet.  A couple of questions:

1.  Is this normal?
2.  Will everything be okay if I disconnect the power to the switched power?  Will it damage the monitor or marquee?  I've heard that it's not good to run the switched power without the board, but is it okay for the isolation transformer to run without a "full load"?

Thank you in advance for any responses.
Chris

[RayB]

Well, if you disconnect power to the switcher, your game won't work anymore. How about posting photos and explain what your end goal is? Are you mame-ing this?  How old is the monitor? (maybe it doesn't need an iso)

[coliveira]

Thank you very much for the response.  Yes, I am trying to mame the machine, but I would really like to do it in a way that doesn't destroy it and can easily be turned back into Ultimate MK3.  To me, the easiest way would be to remove the switched power and put the computer there.  It would be very easy to switch it back and forth as long as this were feasible.  However, it appears to be getting 130 volts of AC instead of 120.  Basically, it's going to be a gift for my nephews that would probably be turned back into Ultimate MK3 when they were older.  Based on the faded side art, my guess is that this was once a MK2 game.  I've included some pics of what I'm looking at and the wiring for MK2 from an online instruction manual.  I get a bit lost with what happens to the power at the 15 pin connector.  Hopefully the pictures will work...

MK2 Power Wiring Diagram



The power in and isolation transformer.  By the way, what is that below the isolation transformer?  It appears to be a fuse of some sort, but is it a filter as well?



The Switched Power Supply.  This is where I'm hoping to put the computer.  By the way, it appears to be getting 130 volts of AC instead of 120.  Does this matter?



Side A of isolation transformer



Side B of isolation transformer



Thank you very much for looking and hopefully you can help!
Chris

[coliveira]

Apparently I'm not so good with the pics!

Here's some links:

http://www.flickr.com/photos/20507832@N05/5393909677/#in/photostream/
http://www.flickr.com/photos/20507832@N05/5393909841/#in/photostream/
http://www.flickr.com/photos/20507832@N05/5393910019/#in/photostream/
http://www.flickr.com/photos/20507832@N05/5394507264/#in/photostream/
http://www.flickr.com/photos/20507832@N05/5394507056/#in/photostream/

Hopefully the links work.  I've never really used flickr (or anything like it before)...

[MonMotha]

MK2 does have everything in the cabinet running of the transformer in the bottom (which also puts out low voltage AC for the coin door lamps).  It's no real harm, but I wouldn't trust it to run an entire PC.  PCs draw a chunk of juice.  Switch-mode power supplies are isolated in and of themselves, so running it off the isolation transformer that's powering the monitor does no real harm, but it does add load to the transformer.  The marquee light is of little consequence.

I have been told that the MK2 transformer actually has two separate output windings.  One was intended for the monitor and the other "everything else", but that's not how the cabinets got wired up in the real world.  Again, it's of little consequence, though your marquee light might shock you.  Fortunately, it's covered.

As for the 130V at the output, that's because it's configured for 110V input and 120V output, but your AC line voltage is closer to 120V.  The discrepancy arises because the AC line voltage in the USA has slowly increased since that cabinet was made.  110V was common back then, especially in older buildings with heavy electrical loads (like arcades), while everything in the cabinet was designed for 120V as that was the new "ideal" going forward.  It's probably not a huge deal.  Unfortunately, there's no 1:1 option on that transformer, despite it having several input taps.  The best you could do is reconfigure it for 130V (iirc) input, and you'd get about 110V out.  I wouldn't worry about it.

Here's what I'd do: unplug the existing SMPS DC supply and remove it and the boardset.  Install the PC and plug it into a standard wall outlet.  Leave everything else alone.  That's easy to do, easy to go back, and it's pretty "proper".

[coliveira]

Thank you very much for the reply.  I found it extremely helpful and I will go ahead and do that.

Thanks again
Chris

[boardjunkie]

Isn't there a service outlet in the bottom of MK type cabs? Why not just use that to pwr the mame machine (provided its in front of the iso xfmr).

[coliveira]

Not really sure what service outlets look like as far as arcade games are concerned.  Honestly, I've done a little home wiring, but I was a little nervous to mess with the actual arcade wiring.  It seemed easier and cleaner to use MonMotha's basic idea than to mess too much with the existing wiring.

I'm sure there were easier ways though.  Unfortunately that's never been my style.

Thanks for the post.
Chris

[boardjunkie]

Just a single 110v outlet on a metal mtg plate somewhere near the iso xfmr. I *swear* Midway cabs of that era had one....I remember using them for plugging in a soldering iron.....

[coliveira]

Hmmm... I looked (mostly hoping I didn't miss it the first time around!), but I couldn't find anything.  Obviously it's entirely possible that this thing has been rewired though.  Also, I have a new post regarding my freaking out joystick that I'd love for you to check out...

Thanks
Chris

[MonMotha]

I know that MK2 does not have one.  I don't think NBA Jam did, either.  I think some of the later ones (Blitz era) may have.