my apple mac pro desktop will not turn on

The following check list is from the cube engineers manual.

One can imagine why this scenario occurs when you consider that the ATI card must (somehow) be connected to the power-on logic/signals because it also has an ADC connector (that supports powering on/off the system via an Apple monitor).Īnyway, I hope this helps someone. when the system is powered down (e.g., by removing the A/C power cord) and then the power button is pressed (while the VGA cable is connected via the DVI-to-VGA adapter) the system will not not start up until the VGA cable is temporarily removed when the VGA cable is connected and you attempt to shut the system down, the system will shutdown then immediately reboot (i.e., seemingly can't be shut down) I've found that using some VGA cables (i.e., wired to indicate some monitor sizes), but not others, will cause the following behavior (sorry, I've not figured which is which): VGA cables have some pins that are either present/wired or not because they are used to indicate the 'kind'/size of montior (VGA, XVGA, etc. It turns out that some of the ATI Radeon graphics cards (e.g., the 9000 in our ol' DualGig MDD) can cause/exhibit these problems when using the DVI-to-VGA adapter with certain kinds of VGA cables.

Your problems might be related to the following: This is a copy of an email I sent in response to a mailing-list posting about a system that sometimes spontaneously re-boots after being shut down and sometimes won't boot when the power button is pressed (it was a MDD PowerMac). I would hazard a guess that Apple may be tired of all the warranty logic board replacements that they've done because the user did an improper PMU reset.)

It's reset by simply unplugging the power cord for 15 seconds. (Note: Apple appears to be dispensing with the PMU - the newest G5s have a SMU (System Management Unit) which handles most of the same tasks but does not have a reset button. BTW, thanks for posting the official procedure. Granted, this is just a correlation and not a proven cause and effect - more likely these folks may have just had an ESD incident while they were dinking around inside their machines or the MLBs had already failed in some other way - but why take chances? If a little fear causes people to be conservative and extra careful when messing around with a part that's US$300-500 to replace, that's less harmful misinformation than the many and varied PMU reset procedures that get propagated here and other places on the web. I have had a number of clients with un-revivable logic boards who've told me that before bringing their machines in for service, someone they knew told them to either hit the PMU reset button several times in a row or even to hold it down for thirty seconds or more. Sure to reset the time, date, and other system parameter settings. The above procedure resets the computer's PRAM. 'System' section of 'Symptom Charts' in this chapter. The computer does not power on, there is something else wrong with it refer to the Wait ten seconds before connecting the power cord and powering on the computer. Reset button a second time because it could crash the PMU chip.ģ. Press the PMU reset button once and then proceed to step 3. If the battery is good, go directly to step 2.Ģ. If the battery is bad, replace it, wait ten seconds, and then Disconnect the power cord and check the battery in the battery holder. When you have aĬomputer that fails to power up, follow this procedure before replacing any modules:ġ. Many system problems can be resolved by resetting the PMU chip. If the PMU crashesĪnd is not reset, the battery life goes from about five years to about two days.įor the location of the PMU reset button, see 'Logic Board Diagram' in the Views Touching the circuitry on the logic board can cause the PMU to crash. Â€¢ manage system resets from various commands.īe very careful when handling the logic board. Â€¢ tell the computer to turn on, turn off, sleep, wake, idle, etc. The PMU (Power Management Unit) is a microcontroller chip that controls all powerįunctions for this computer. The most you can do crashing PMU is to expire the battery.įor those that want the official procedure for resetting the PMU here it is. I don't know where the myth came from that suggests if you crash your PMU you need to replace your logic board but it's not true.

My apple mac pro desktop will not turn on