3 amps is easily enough
IIRC it the CPU board takes a few 100mA

You don't really need a dual voltage power supply.

5V at 3A is more than enough for most MPUs you will be testing.

I use a small 5V 3A plug pack type switching supply worth about $5 - your concept is overkill unless you intend testing/repairing professionally?

Your measurements are next to useless useless we know a LOT more detail:

What board are we talking about?
What else was connected to it when measured?
What parts have been replaced on this measured board (some compatible parts that might have been used in a repair draw more current than others even at idle)?

Many more things.................

The first sentence in the original post says they're working on a WPC CPU 89. I'm going to go out on a limb and guess that measurements were made at connector J210 (mentioned above) on the CPU board.

Those readings sound about right. Don't go over 1 amp on either. If a component goes bad on the CPU, it can draw considerably more and/ or blow a fuse. I'm assuming you're working with a known good CPU board. J210 comes from the factory with 18 gauge wire. Probably can get away with smaller on the bench, but best to stick with factory.

Sure, I agree with your assumption but there are still too many unanswered questions.

Is this an original PCB with all original parts or have some chips been replaced? If some HCT ICs have been replaced with LS types or vice versa, this would change the current draw overall. Same issue if the RAM has been replaced with NVRAM or a different brand RAM.

It's nice to have a ballpark figure but the trouble with that is you will then have some people chasing a 'magical' figure (in this case) of 500ma when their board might draw 550ma or even 480ma and be perfectly normal.

I appreciate your enthusiasm!

I guess the question is, how much of this kind of work are you planning on doing?

If you are only working on your own machines, you can do a quick go no-go test with +5v and +12v, I use a twenty year old arcade power supply, but I've used an old computer power supply to do the same thing. Your 0-30V dual supply is great for this, because you'll rarely find yourself needing more than an amp or two of +5v and less than that on the +12v.

Then you just use your machine to test everything else, because your machine will have all the voltages you'll need to test it's boards.

If you are planning upon testing other people's boards and you don't have a machine to plug them into, then you can do some limited testing with a bench supply, but most people start thinking about finding a machine of that generation with a cabinet that is destroyed and salvage the wiring harness and all the boards.

So if they are working on WPC-89 boards, they have a complete set of WPC-89 boards and wiring. This allows you to fully test the suspect part in a known good system.

After a few more years you end up with a complete test system for System 11 pinballs, Bally pinballs from the 80's, Gottlieb System 3's, Data East Pinballs, Stern Whitestar pinballs, etc...

It just depends upon how much you plan to do.

For your immediate question, yes, your supply will be just fine for a quick test to see if the LED's start blinking.

As for how much current... well, I mostly don't care. If the go no-go test gets the LED's blinking, and nothing gets obviously hot I just plug the board back into the machine (or my full-system test bench) and see if everything's working.

I can't think of any board I've worked on where I've made a point of writing down how much current something uses (OK, one board, an NSM Jukebox amplifier from the 70's that the schematic specified exact bias current to the base of the output transistors).

For pinballs pretty much anything that is using too much current will get hot, and THAT is what I check for. Checking if things get hot identifies the specific problem you've got. Trying to match expected current drain to a particular board sample... it just isn't too helpful in my troubleshooting. As the other poster's have suggested, there can be a lot of reasons why a particular board might be using more current without actually having any functional problem.

A lot of us have a dream of having a complete test bench for every pinball system we work on. With your nice benchtop power supply you are well on your way!