Turning on Mac Mini SMPS power supply?

Or am making a presumption here?

With the ac adapter plugged into the motherboard and an ac outlet, I get no dc voltages at the PCB connector pins. Using another known good adapter gives the same results.

So I presume (correctly?) that the adapter is turned on via the sense pin.

What turns this adapter on?

Thanks.

Your assumptions are correct. If this was a PS for a PC, I would say pulling the green wire to common will start the supply. Not sure what color MAC uses for this.

Jamie sez:

I've identified the wire. No problem there.

But, since this pin is pulled low by circuit(s) on the motherboard, I can't just tie it low. So as to not damage the driver circuits, the best I can do is pull it low with a pull-down resistor, which I tried and doesn't work.

So:

1. pin in PS needs to be pulled to ground.
2. pin on motherboard needs a pull-down resistor.

So I guess the only solution is to hack the adapter's dc cable and

1. add a pull-down resistor to the motherboard's sense pin (many "Mini in my car" blogs describe this as required to get the Mini to boot)
2. cut the dc cable and tie the PS's sense pin to ground.

Other ideas?

Thanks.

Original issue:

Mac will not boot. Probably because the smps would not be turned on by the iSense line.

So:

1. I cut the sense line
2. Pulled the Mac's end of the line low with 3R3 resistor
3. Tied smps' end to ground.

With the smps connected to mains, output is 18vdc.

When smps is connected to Mac (just the dc power + and -) the smps quits (0v). Doesn't matter whether I start the smps before connection or after.

The dc input terminals on the Mac motherboard measure 6k ohms.

Why is the smps quitting?

I'd use a bench supply to test but they (and the rest of my tools) are 2000 miles away.

Ideas?

Thanks.

18 volts does not sound good. place a load on that output like a incandescent house lamp. then test voltage on it.