G4 will not boot with ADC monitors but does with VGA.

[torvan]

Okay, I have a G4 1.0 Ghz machine with a GeForce 4MX card in it.   If I try to use any ADC monitor, it will never boot. If I use VGA, it boots fine. If I boot it with the VGA monitor and then plug in either the 15" ADC or the 23" ADC, it will shut off immediately.

If I put in an ATI 7500 in the AGP slot, the same thing happens.

So it would appear ADC will not work on my machine. Any ideas at this point?

[GaryN]

Probably a PSU 28vdc issue. There's a lead in the ADC that powers the monitors (of course, you knew that). If that fails, no boot because the GPU can't detect a monitor that's not powered. Check for voltage with computer off - it's standby, should be there.

MDD = Pin 14 White
QS = Pin 22 White or Purple

[DieHard]

Gary is spot on as usual. I have had this issue.  Sometimes the PS and sometimes the Lead is not in the harness all the way. 

Carefully unplug the Power supply connector at the MB and make sure the pins are equal length in the harness

[reader50]

It sounds like the power supply has weakened, and is unable to pick up the monitor load. If it were just a no-power problem, the ADC monitors would fail to power up when you plug them in. But the Mac would continue to run headless. An actual shutdown happens when the PS cannot maintain the output voltage, and shuts down to prevent undervoltage damage.

A dried-out cap in the PS could cause this. See the Capacitor Plague entry - a bad electrolytic cap is often easy to see. Not terribly hard to replace either, if you have soldering skills.

[torvan]

Well, a visual inspection of the power cable doesn't show anything odd to my eyes, nor does the connector. I do not own a voltimeter currently--but will towards the end of the week and said cost is justifiable for every component in the house really.

I will pull the PS and look for busted/bulged caps--but my soldering skills are right up there with my ability to fly to Mars--meaning I have none.  So if I see any bulged or leaking or busted or dried out caps, I need to find someone locally who can do the replacement I guess.

[DieHard]

Well, a visual inspection of the power cable doesn't show anything odd to my eyes, nor does the connector. I do not own a voltimeter currently--but will towards the end of the week and said cost is justifiable for every component in the house really.

I will pull the PS and look for busted/bulged caps--but my soldering skills are right up there with my ability to fly to Mars--meaning I have none.  So if I see any bulged or leaking or busted or dried out caps, I need to find someone locally who can do the replacement I guess.

The 28V still has to "pass thru" the Logic board, so cannot rule out a Logic Board or AGP slot issue also, I should have mentioned that

Definitely, look at all the prongs in the AGP slot and use contact cleaner