Turning on Mac Mini SMPS power supply?

[notme]

The Mac Mini ac adapter is off until the Mini commands it to turn on via the
iSense pin in the power connector.

What does the iSense pin need in order to start the external SMPS ac adapter?

Pull low? High (5v)? Or...?

Googling turns up lots of info on people who have used the Mini in cars and
have tied the Mini's iSense line low (using pull-down resistor) but they're
not using the ac adapter.

A better forum to ask this question?

Thanks.

 

[notme]

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.

 

[Jamie]

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.

 

[notme]

Jamie sez:

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.

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.

 

[notme]

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.

 

[Jamie]

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.