JPAC and PSU - what to unplug?

[Arch]

The JPAC instructions tell me to remove the power supply from my JAMMA connector when plugging in the JPAC. I have skimmed a lot of threads which is related to this, but I can't find a solution to my specific problem. Please refer to the attached picture. As you can see the the mains go straight into the PSU. The cables from the five topmost screws go to the JAMMA connector, while the remaining wire go to the monitor. Some of the monitor cables go via a big metal box which I assume is the "DO NOT REMOVE THIS!!!"-isolating transformer. I think the PSU is fairly new, but the isolating transformer seems older.

So the question is, what can I unplug? Shall I leave the grounds going to the JAMMA connector? Can I unplug the +12V 2.5A, the -5A1a and the two cables connected to the +5V15A and leave the monitor related cables as is? Do I really have to unplug anything at all? Help a poor n00b who loves arcade games but has never touched a soldering iron.  

[BobA]

To isolate the power supply just take off the ac ac and gnd and transfer them to a 3 terminal strip so your cab still has AC. This will power the monitor and leave all your AC wiring intact.  Transfer the wires one terminal at a time so none of the lines get mixed up.  At this point there is no power coming from the PS and you can leave all the wires to the jamma connector connected.

[Arch]

Thank you so much for your answer, BobA! I will get hold of a terminal strip tomorrow and give it a go!

[mgb]

I'm not sure I follow.
Isn't it just that the instructions are referring to the power being off while plugging in or unplugging the jpac?
Am I missing something (always very possible)?
why pull any power cables off?

[BobA]

I'm not sure I follow.
Isn't it just that the instructions are referring to the power being off while plugging in or unplugging the jpac?
Am I missing something (always very possible)?
why pull any power cables off?

This is the info on the Ultimarc site.

It is usually preferable to remove any low-voltage game board power supply which is fitted inside a JAMMA cabinet, leaving only the monitor powered from AC mains (via the cabinet isolating transformer if fitted)

[mgb]

Oh ok, I get it.
I assumed that you can just let the 5volt, etc stay.
I did miss something

[Arch]

@BobA: Worked like a breeze! I had the fire exstinguisher at the ready when plugging it in, but I had no hassle at all, so thanks! 
On a sidenote, the isolating transformer gives off a constant high pitched hum of sorts. It also did this before I did the rewiring. Is this normal?

[BobA]

The very noticeable hum or whine is often due to the laminations in the transformer getting a bit looser with age.  Seems to be a common problem with older units.  Don't think there is much you can do about it except replace the transformer.  Even some newer transformers hum a bit.

[mgb]

here's an article from Bob Roberts about that
http://www.therealbobroberts.net/iso.html