Zombie iMac 21.5": refuses to power on for hours

This has happened twice to my 21.5" iMac (mid-range): After writing to disk for hours, I power down the iMac in the evening via Apple menu, disconnect the cables, carry it to another room, connect the power cable, but the iMac refuses to power on.
Measures: verified cable connections, electrical power outlet, reset SMC. Result: iMac refuses to power on.
Solution: disconnect all cables, wait till morning, connect power cable, press power button. Result: No issues, works fine.
Any idea why this happens? Have you experienced this?

Hi, just to share I experience the same thing.
One month ago this happen to me when I power off the socket power (the power to the plug of my iMac 27"). When I power on the socket power and press the power button behind the screen, no respond at all. Tried various method suggested at support site but no improvement. Finally I gave up go to bed and next morning it power up perfectly fine.
After this I use iMac for a month without power down the main socket it work perfectly fine whenever I power up or power down using the push button behind the screen. Just 15 mins before this post, I came back home, the iMac still cool as it not been turn on. I power off the main socket, remove the power plug, put back the power plug again, turn on the main socket power, press the power button behind the screen, no respond at all. Sign......do I need to wait till next morning then can power up again? Sign............
What shall I do?
Do I have to restrict myself do not power down the main socket power so that I can use the iMac as and when I like.
Shall I send for Servicing?
Somebody please help.

Similar Messages

Intel iMac shutting off suddenly, not coming back for hours

Hello,
Last night my iMac suddenly shut off; I tried for about twenty minutes to turn it back on (I tried the power button, unplugging and replugging, changing outlets...), then gave up. This morning I tried it and it worked just fine, but after several hours it shut off again. That was about three hours ago and it hasn't come back yet. Curiously it shut off right before iSight was going to snap a picture in Photo Booth, and I just can't remember if that's when it happened last night too...
Any help?

Sounds like an overheating problem. You could try to reset the SMC and see if that helps, if not it probably needs to go to the shop.
Here is a link to how to reset the SMC on a new Mac
http://docs.info.apple.com/article.html?artnum=303446

IMac G3 computers still refusing to power up? Here is a solution.

This post is the sequel to the discussion "iMac G3 computers still refusing to power up? Here is what I've found out!", accessible under this link http://discussions.apple.com/thread.jspa?threadID=2326420&tstart=0 .
I made it! I have fixed the issue of the iMac DV refusing to power up.
For this, I had to design and build a prototype of a cost-effective nonresident hardware patch, which I am about to describe in this article. I will also give the instructions of use. Subsequently, I will expose the rationale, which led to the background of the design. Finally, I will report the observations after the experiment with the patch and sketch the theory of its actual operation with the PMU firmware.
*TABLE OF CONTENTS*
1. Applicability condition and restriction
2. Description of the PMU hardware patch
3. Interconnections of the PMU microcontroller with the PMU Hardware Patch
4. Instructions to read before mounting and unmounting the PMU Hardware Patch on the iMac
5. Background to the design of the PMU Hardware Patch
5.1. The genesis
5.2. What the PMU Hardware Patch actually does
6. Recommended updates before using the PMU Hardware Patch
7. User's Manual of the PMU microcontroller
8. Datasheets of the 74HC4049 Hex inverting high-to-low level shifter
9. Datasheets of the 74HC193 Presettable synchronous 4-bit binary up/down counter
10. Errata to the discussion start of February 6th, 2010
h1. 1. Applicability condition and restriction
The hardware patch addresses the issue of a slot-loading iMac, which can be powered up only within two seconds after resetting the PMU microcontroller. It is not required otherwise.
Moreover, it does not need to reside in the iMac, but suffices once to permanently cure the power-management firmware.
h1. 2. Description of the PMU hardware patch
As seen on figures 1 and 2, the PMU hardware patch relies on a low part count: two logic ICs (74HC193 and 74HC4049), two 0805-packaged resistors and two 1206-packaged capacitors, which all fit on a 31mm x 45mm single-sided SMD prototyping board. The circuit consumes a current intensity of about 7.5 milliamps for a supply voltage of 3.3 volts.
The PMU hardware patch functions as a frequency divider of the PMU sub-clock generator output, XCOUT. It applies an active low pulse to the PMU NMI_bar non-maskable input, once every sixteen XCOUT rising edge for half a period. It is disabled when the PMU main clock generator output, XOUT, returns to 0 by oscillations, or when the system is being reset with the PMU RESET_bar input asserted to 0. The peak-to-peak 1.5-Volt oscillations of XCOUT are fed through the 1-nanofarad DC-blocking capacitor to the inverter biased in the linear region by a feedback resistor of twice 270 kilo-ohms, for translation to 3.3V-compatible logic levels.
The power-supply bypass capacitor amounts to 100 nanofarads.
*Figure 1: Schematics of the PMU Hardware Patch*
[Figure 1|http://www.flickr.com/photos/aegidius_2/4923600713/in/photostream/|Click to view in a new tab.]
Note the 0.5mm-diameter insulated copper wires in ochre color on the prototype board (figure 2).
*Figure 2: Picture of the PMU Hardware Patch prototype - component side*
[Figure 2|http://www.flickr.com/photos/aegidius_2/4924196064/in/photostream/|Click to view in a new tab.]
The 10cm-long interface wires can be clamped to the board with cylinder blocks made of epoxy glue (Araldite), as seen on figure 3.
*Figure 3: Picture of the PMU Hardware Patch prototype - interface side*
[Figure 3|http://www.flickr.com/photos/aegidius_2/4924196296/in/photostream/|Click to view in a new tab.]
h1. 3. Interconnections of the PMU microcontroller with the PMU Hardware Patch
The PMU Hardware Patch uses the signals RESET_bar, NMI_bar and the clocks XOUT and XCOUT of the PMU microcontroller, U34 on the Logic Board underside. Both are supplied by the voltage available across the tantalum capacitor C131.
Pin 73 of U34 performs the function INT3_bar because it turns out to be permanently configured as an edge-sensitive interrupt input, once the PMU Hardware Patch has been used. This will be justified in section 5.2. When the computer is plugged to the mains, a pressure on any power button can induce a falling edge on pin 73. U34 responds by asserting pin 75 to logic 0, as long as the computer has to remain powered on from the PAV board.
Pin 10 of U34 is the active low reset input, RESET_bar. It toggles from logic 0 to 1, a few hundred milliseconds after U35 has detected the supply voltage across the capacitor C131 has settled above 2.2 volts, either because a good battery has been inserted in the holder, or else because the computer has been plugged to the mains and the trickle power from the PAV board, T5V, is available. It is also asserted to logic 0, as long as the PMU reset button is depressed.
Pin 9 of U34 is the sub-clock output, XCOUT. The PMU microcontroller selects it for its operation in low-power dissipation mode to carry on the timekeeping, normally as soon as the computer is being shut down. The microcontroller shall then draw no more than 40 microamps typically from the battery.
Pin 11 of U34 is the main clock output, XOUT. It is the default clock of the PMU microcontroller after the reset phase. The microcontroler selects it for its operation in high-speed mode, when the computer is powered on.
Pin 15 of U34 is the active low edge-sensitive non-maskable interrupt, NMI_bar. It is normally unused and its voltage remains pulled up to the microcontroller supply through resistor R124. However, it happens to help resolve the power-up issue when it is controlled by the PMU Hardware Patch. The justifications are exposed in section 5.2.
Figure 4 shows an easier access to the clock and control signal pins of U34, to be connected to the PMU Hardware Patch, from the top of the Logic Board. You will have to solder the PMU Hardware Patch interface wires at the locations pointed to.
*Figure 4: View of the access to the PMU U34 chip signals for the PMU Hardware Patch*
[Figure 4|http://www.flickr.com/photos/aegidius_2/4929783304/in/photostream/|Click to view in a new tab.]
h1. 4. Instructions to read before mounting and unmounting the PMU Hardware Patch on the iMac
All possible updates accessible from the links in section 6 shall be installed. Then remove the battery. All this ensures your iMac will be prepared to interact with the PMU Hardware Patch under the same initial conditions as in the experiment I have carried out.
Afterwards, remove the bottom housing, the metal shield, the SDRAM, the IDE cable and disconnect the hard-drive power cable. Take off the Logic Board together with the Down Converter board and the modem and place it on your workbench. Now carefully solder the PMU Hardware Patch interface wires at the locations pointed to in figure 4. Figure 5 illustrates the result.
Install the boards back in the iMac, reconnect the hard-drive power cable and the IDE cable, and re-insert the SDRAM in its original slot. Put the computer on a large flat and safe area near a power socket. Stand up the PMU Hardware Patch on a plastic pouch, to insulate it for the parts of the Logic Board, as seen in figure 6. Connect the keyboard and the mouse.
Once you have plugged the computer back to the mains, don't take the risk to touch the computer except the keyboard and the mouse, because quite a few visible metal parts are live and lethal by body contact!
Wait for twenty seconds and then unplug the computer from the mains. Wait for a minute. Again, supply the mains to the computer and wait for twenty seconds, before you press the power button on the keyboard. Then let the operating system load until you can see the menu bar. Maybe a window will pop up to warn you that the system date is too ancient, but you can skip it. Now shut down the computer by selecting the command in the Special menu. I know it is awkward to move the mouse pointer when the picture is upside down. But take it easy!
Unplug the computer from the mains and unmount the PMU Hardware Patch. Once you have re-assembled your iMac, you can power it up and use it without the constraint to reset the PMU each time before and then to press on a power button in a hurry within two seconds.
A good tip: get all this task cleanly done by a professional, like a repairman or an electronics technician, if you feel you don't have enough skill in soldering!
*Figure 5: View of the Patch-PMU interconnections*
[Figure 5|http://www.flickr.com/photos/aegidius_2/4929190683/in/photostream/|Click to view in a new tab.]
*Figure 6: View of the mounted PMU Hardware Patch*
[Figure 6|http://www.flickr.com/photos/aegidius_2/4929190963/in/photostream/|Click to view in a new tab.]
h1. 5. Background to the design of the PMU Hardware Patch
h2. 5.1. The genesis
My idea to the design of the PMU Hardware Patch started with the study of the user's manual of the PMU microcontroller and with my observations on the clocks XOUT and XCOUT.
The symptom of the power-up default was accompanied by the disappearance of the clocks XOUT and XCOUT, if no power button was depressed within two seconds after pushing on the PMU reset button. I concluded, it was the reason why the PMU microcontroller could no longer react to a power button signal on pin 73 (P15/D13/INT3) and perform any timekeeping until the next PMU reset.
By looking at the block diagram Figure 1.10.3 (Clock generating circuit) of the microcontroller user's manual, I noticed that any clock oscillator, XOUT and XOUT, can be re-enabled after the CM10 bit has pulsed to logic 1, provided that the SR latch is reset by the NMI_bar non-maskable interrupt line or by the RESET_bar input. If bit CM04 was set to logic 1, then XCOUT resumes the clock oscillations, and likewise for XOUT if bit CM05 was set to logic 1.
I assumed the situation CM04 = 1 and CM05 = 0, as the PMU microcontroller enters the STOP mode. My idea was then to let it avoid the STOP mode and continue operating in the low-power dissipation mode, by periodically refreshing the SR latch reset through a low pulse on the NMI_bar input. Since the 32.768-kHz oscillations on XCOUT fade within a few hundred microseconds, repeating the pulse on NMI_bar at a quicker rate, once every 488 microseconds (i.e. once every sixteen XCOUT clock period) is acceptable.
However, I could not foresee how the non-maskable interrupt routine would interfere with the PMU firmware, whenever the NMI_bar pulse would be acknowledged to let the microcontroller program counter branch to it. I know that events on edge-sensitive interrupt lines are normally latched, which allows the microcontroller state machine to detect them even if they are too short compared to the clock period. And yet, I assumed it differently, after reading this excerpt in the microcontroller user's manual in the section "Precautions for Interrupts": "Signals input to the NMI pin require an “L” level of 1 clock or more, from the operation clock of the CPU". I decided to design and build a PMU Hardware Patch, that would generate a pulse on NMI_bar for a duration of less one XCOUT clock period, actually for half of it. If it is synchronised with the appropriate edge of XCOUT, then maybe the pulse would not cause the branch to the NMI routine. Moreover, when both XOUT and XCOUT are running, the duration of the pulse from the PMU Hardware Patch would exceed the period of the XOUT clock. To avoid the risk that the pulse occurs for more than one period of XOUT, as the operation clock of the microcontroller, I designed the PMU Hardware Patch, so that it remains inactive as long as XOUT is not steadily asserted to logic 1. The PMU Hardware Patch will not either generate any low pulse during the reset phase, as long as RESET_bar is asserted to 0, and as required in the microcontroller user's manual.
Once the PMU Hardware Patch assembled, I took the risk to use it in the iMac DV. What a relief it was, whenever I turned on the computer again, without the need to press the PMU reset button each time. The PMU Hardware Patch works!
After a power cycling of one minute, without unplugging the iMac from the mains, I looked at the time and date I had initially set. The time had not advanced correctly, while the computer was turned off. Instead it was lagging: it recovered with the value I had initially entered, plus about one minute that the operating system takes to load. That means that no clock was running again, while the computer was turned off. Nonetheless I unmounted the PMU Hardware Patch and tried power cycling the computer at any time interval. Powering it on always succeeded without the need anymore to reset the PMU microcontroller before each attempt.
h2. 5.2. What the PMU Hardware Patch actually does
This means the PMU Hardware Patch had definitely interfered with the PMU firmware and cured it with respect to the power-up issue once and for all. I have figured out it interrupts the firmware through the NMI routine, which restores a few data in the non-volatile FLASH memory. These data are used to program the interrupt control register INT3IC, so that pin 73 behaves as the edge sensitive interrupt INT3_bar. This eliminates the need to have any clock running to register a request on pin 73 to power up the computer. Furthermore, when INT3_bar senses a low pulse because a power button is being pushed on, it urges the internal signal "Interrupt request level judgment" to reset the SR latch register, which re-enables any clock oscillator, as seen in figures 1.11.9 (Maskable interrupts priorities (peripheral I/O interrupts)) and 1.10.3 (Clock generating circuit). The PMU microcontroller can resume its operations and look for the source of the interruption. It finds out it has to power up the iMac, because INT3_bar had been latched in as active.
h1. 6. Recommended updates before using the PMU Hardware Patch
+Mac OS 9: Available Updates+
http://support.apple.com/kb/HT1387
+Power PC-based iMac: When to install available updates+
http://support.apple.com/kb/HT2560?viewlocale=enUS&locale=enUS
+iMac: How to Install an iMac Firmware Update+
http://support.apple.com/kb/HT2561
h1. 7. User's Manual of the PMU microcontroller
http://documentation.renesas.com/eng/products/mpumcu/62aeum.pdf
h1. 8. Datasheets of the 74HC4049 Hex inverting high-to-low level shifter
http://www.nxp.com/documents/datasheet/74HC4049CNV.pdf
http://www.st.com/stonline/products/literature/ds/1965/m74hc4049.pdf
http://www.ti.com/lit/gpn/cd74hc4049
http://www.fairchildsemi.com/ds/MM/MM74HC4049.pdf
h1. 9. Datasheets of the 74HC193 Presettable synchronous 4-bit binary up/down counter
http://www.nxp.com/documents/datasheet/74HCHCT193.pdf
http://www.ti.com/lit/gpn/cd74hc193
h1. 10. Errata to the discussion start of February 6th, 2010
1. "PRAM battery": Wrong naming! The Logic-Board battery only serves to support the timekeeping operation when the mains is removed from the computer, whereas the PRAM data are stored in the non-volatile FLASH memory of the PMU microcontroller (in slot-loading iMacs).
2. "(...) sets bit 1 of the CM1 register (system clock control register 1) to 1 (...)". This fragment shall rather read: "(...) sets bit 0 of the CM1 register (system clock control register 1) to 1 (...)".
Aegidius_2
Keep perseverance and reach your goal!

This post is the sequel to the discussion "iMac G3 computers still refusing to power up? Here is what I've found out!", accessible under this link http://discussions.apple.com/thread.jspa?threadID=2326420&tstart=0 .
I made it! I have fixed the issue of the iMac DV refusing to power up.
For this, I had to design and build a prototype of a cost-effective nonresident hardware patch, which I am about to describe in this article. I will also give the instructions of use. Subsequently, I will expose the rationale, which led to the background of the design. Finally, I will report the observations after the experiment with the patch and sketch the theory of its actual operation with the PMU firmware.
*TABLE OF CONTENTS*
1. Applicability condition and restriction
2. Description of the PMU hardware patch
3. Interconnections of the PMU microcontroller with the PMU Hardware Patch
4. Instructions to read before mounting and unmounting the PMU Hardware Patch on the iMac
5. Background to the design of the PMU Hardware Patch
5.1. The genesis
5.2. What the PMU Hardware Patch actually does
6. Recommended updates before using the PMU Hardware Patch
7. User's Manual of the PMU microcontroller
8. Datasheets of the 74HC4049 Hex inverting high-to-low level shifter
9. Datasheets of the 74HC193 Presettable synchronous 4-bit binary up/down counter
10. Errata to the discussion start of February 6th, 2010
h1. 1. Applicability condition and restriction
The hardware patch addresses the issue of a slot-loading iMac, which can be powered up only within two seconds after resetting the PMU microcontroller. It is not required otherwise.
Moreover, it does not need to reside in the iMac, but suffices once to permanently cure the power-management firmware.
h1. 2. Description of the PMU hardware patch
As seen on figures 1 and 2, the PMU hardware patch relies on a low part count: two logic ICs (74HC193 and 74HC4049), two 0805-packaged resistors and two 1206-packaged capacitors, which all fit on a 31mm x 45mm single-sided SMD prototyping board. The circuit consumes a current intensity of about 7.5 milliamps for a supply voltage of 3.3 volts.
The PMU hardware patch functions as a frequency divider of the PMU sub-clock generator output, XCOUT. It applies an active low pulse to the PMU NMI_bar non-maskable input, once every sixteen XCOUT rising edge for half a period. It is disabled when the PMU main clock generator output, XOUT, returns to 0 by oscillations, or when the system is being reset with the PMU RESET_bar input asserted to 0. The peak-to-peak 1.5-Volt oscillations of XCOUT are fed through the 1-nanofarad DC-blocking capacitor to the inverter biased in the linear region by a feedback resistor of twice 270 kilo-ohms, for translation to 3.3V-compatible logic levels.
The power-supply bypass capacitor amounts to 100 nanofarads.
*Figure 1: Schematics of the PMU Hardware Patch*
[Figure 1|http://www.flickr.com/photos/aegidius_2/4923600713/in/photostream/|Click to view in a new tab.]
Note the 0.5mm-diameter insulated copper wires in ochre color on the prototype board (figure 2).
*Figure 2: Picture of the PMU Hardware Patch prototype - component side*
[Figure 2|http://www.flickr.com/photos/aegidius_2/4924196064/in/photostream/|Click to view in a new tab.]
The 10cm-long interface wires can be clamped to the board with cylinder blocks made of epoxy glue (Araldite), as seen on figure 3.
*Figure 3: Picture of the PMU Hardware Patch prototype - interface side*
[Figure 3|http://www.flickr.com/photos/aegidius_2/4924196296/in/photostream/|Click to view in a new tab.]
h1. 3. Interconnections of the PMU microcontroller with the PMU Hardware Patch
The PMU Hardware Patch uses the signals RESET_bar, NMI_bar and the clocks XOUT and XCOUT of the PMU microcontroller, U34 on the Logic Board underside. Both are supplied by the voltage available across the tantalum capacitor C131.
Pin 73 of U34 performs the function INT3_bar because it turns out to be permanently configured as an edge-sensitive interrupt input, once the PMU Hardware Patch has been used. This will be justified in section 5.2. When the computer is plugged to the mains, a pressure on any power button can induce a falling edge on pin 73. U34 responds by asserting pin 75 to logic 0, as long as the computer has to remain powered on from the PAV board.
Pin 10 of U34 is the active low reset input, RESET_bar. It toggles from logic 0 to 1, a few hundred milliseconds after U35 has detected the supply voltage across the capacitor C131 has settled above 2.2 volts, either because a good battery has been inserted in the holder, or else because the computer has been plugged to the mains and the trickle power from the PAV board, T5V, is available. It is also asserted to logic 0, as long as the PMU reset button is depressed.
Pin 9 of U34 is the sub-clock output, XCOUT. The PMU microcontroller selects it for its operation in low-power dissipation mode to carry on the timekeeping, normally as soon as the computer is being shut down. The microcontroller shall then draw no more than 40 microamps typically from the battery.
Pin 11 of U34 is the main clock output, XOUT. It is the default clock of the PMU microcontroller after the reset phase. The microcontroler selects it for its operation in high-speed mode, when the computer is powered on.
Pin 15 of U34 is the active low edge-sensitive non-maskable interrupt, NMI_bar. It is normally unused and its voltage remains pulled up to the microcontroller supply through resistor R124. However, it happens to help resolve the power-up issue when it is controlled by the PMU Hardware Patch. The justifications are exposed in section 5.2.
Figure 4 shows an easier access to the clock and control signal pins of U34, to be connected to the PMU Hardware Patch, from the top of the Logic Board. You will have to solder the PMU Hardware Patch interface wires at the locations pointed to.
*Figure 4: View of the access to the PMU U34 chip signals for the PMU Hardware Patch*
[Figure 4|http://www.flickr.com/photos/aegidius_2/4929783304/in/photostream/|Click to view in a new tab.]
h1. 4. Instructions to read before mounting and unmounting the PMU Hardware Patch on the iMac
All possible updates accessible from the links in section 6 shall be installed. Then remove the battery. All this ensures your iMac will be prepared to interact with the PMU Hardware Patch under the same initial conditions as in the experiment I have carried out.
Afterwards, remove the bottom housing, the metal shield, the SDRAM, the IDE cable and disconnect the hard-drive power cable. Take off the Logic Board together with the Down Converter board and the modem and place it on your workbench. Now carefully solder the PMU Hardware Patch interface wires at the locations pointed to in figure 4. Figure 5 illustrates the result.
Install the boards back in the iMac, reconnect the hard-drive power cable and the IDE cable, and re-insert the SDRAM in its original slot. Put the computer on a large flat and safe area near a power socket. Stand up the PMU Hardware Patch on a plastic pouch, to insulate it for the parts of the Logic Board, as seen in figure 6. Connect the keyboard and the mouse.
Once you have plugged the computer back to the mains, don't take the risk to touch the computer except the keyboard and the mouse, because quite a few visible metal parts are live and lethal by body contact!
Wait for twenty seconds and then unplug the computer from the mains. Wait for a minute. Again, supply the mains to the computer and wait for twenty seconds, before you press the power button on the keyboard. Then let the operating system load until you can see the menu bar. Maybe a window will pop up to warn you that the system date is too ancient, but you can skip it. Now shut down the computer by selecting the command in the Special menu. I know it is awkward to move the mouse pointer when the picture is upside down. But take it easy!
Unplug the computer from the mains and unmount the PMU Hardware Patch. Once you have re-assembled your iMac, you can power it up and use it without the constraint to reset the PMU each time before and then to press on a power button in a hurry within two seconds.
A good tip: get all this task cleanly done by a professional, like a repairman or an electronics technician, if you feel you don't have enough skill in soldering!
*Figure 5: View of the Patch-PMU interconnections*
[Figure 5|http://www.flickr.com/photos/aegidius_2/4929190683/in/photostream/|Click to view in a new tab.]
*Figure 6: View of the mounted PMU Hardware Patch*
[Figure 6|http://www.flickr.com/photos/aegidius_2/4929190963/in/photostream/|Click to view in a new tab.]
h1. 5. Background to the design of the PMU Hardware Patch
h2. 5.1. The genesis
My idea to the design of the PMU Hardware Patch started with the study of the user's manual of the PMU microcontroller and with my observations on the clocks XOUT and XCOUT.
The symptom of the power-up default was accompanied by the disappearance of the clocks XOUT and XCOUT, if no power button was depressed within two seconds after pushing on the PMU reset button. I concluded, it was the reason why the PMU microcontroller could no longer react to a power button signal on pin 73 (P15/D13/INT3) and perform any timekeeping until the next PMU reset.
By looking at the block diagram Figure 1.10.3 (Clock generating circuit) of the microcontroller user's manual, I noticed that any clock oscillator, XOUT and XOUT, can be re-enabled after the CM10 bit has pulsed to logic 1, provided that the SR latch is reset by the NMI_bar non-maskable interrupt line or by the RESET_bar input. If bit CM04 was set to logic 1, then XCOUT resumes the clock oscillations, and likewise for XOUT if bit CM05 was set to logic 1.
I assumed the situation CM04 = 1 and CM05 = 0, as the PMU microcontroller enters the STOP mode. My idea was then to let it avoid the STOP mode and continue operating in the low-power dissipation mode, by periodically refreshing the SR latch reset through a low pulse on the NMI_bar input. Since the 32.768-kHz oscillations on XCOUT fade within a few hundred microseconds, repeating the pulse on NMI_bar at a quicker rate, once every 488 microseconds (i.e. once every sixteen XCOUT clock period) is acceptable.
However, I could not foresee how the non-maskable interrupt routine would interfere with the PMU firmware, whenever the NMI_bar pulse would be acknowledged to let the microcontroller program counter branch to it. I know that events on edge-sensitive interrupt lines are normally latched, which allows the microcontroller state machine to detect them even if they are too short compared to the clock period. And yet, I assumed it differently, after reading this excerpt in the microcontroller user's manual in the section "Precautions for Interrupts": "Signals input to the NMI pin require an “L” level of 1 clock or more, from the operation clock of the CPU". I decided to design and build a PMU Hardware Patch, that would generate a pulse on NMI_bar for a duration of less one XCOUT clock period, actually for half of it. If it is synchronised with the appropriate edge of XCOUT, then maybe the pulse would not cause the branch to the NMI routine. Moreover, when both XOUT and XCOUT are running, the duration of the pulse from the PMU Hardware Patch would exceed the period of the XOUT clock. To avoid the risk that the pulse occurs for more than one period of XOUT, as the operation clock of the microcontroller, I designed the PMU Hardware Patch, so that it remains inactive as long as XOUT is not steadily asserted to logic 1. The PMU Hardware Patch will not either generate any low pulse during the reset phase, as long as RESET_bar is asserted to 0, and as required in the microcontroller user's manual.
Once the PMU Hardware Patch assembled, I took the risk to use it in the iMac DV. What a relief it was, whenever I turned on the computer again, without the need to press the PMU reset button each time. The PMU Hardware Patch works!
After a power cycling of one minute, without unplugging the iMac from the mains, I looked at the time and date I had initially set. The time had not advanced correctly, while the computer was turned off. Instead it was lagging: it recovered with the value I had initially entered, plus about one minute that the operating system takes to load. That means that no clock was running again, while the computer was turned off. Nonetheless I unmounted the PMU Hardware Patch and tried power cycling the computer at any time interval. Powering it on always succeeded without the need anymore to reset the PMU microcontroller before each attempt.
h2. 5.2. What the PMU Hardware Patch actually does
This means the PMU Hardware Patch had definitely interfered with the PMU firmware and cured it with respect to the power-up issue once and for all. I have figured out it interrupts the firmware through the NMI routine, which restores a few data in the non-volatile FLASH memory. These data are used to program the interrupt control register INT3IC, so that pin 73 behaves as the edge sensitive interrupt INT3_bar. This eliminates the need to have any clock running to register a request on pin 73 to power up the computer. Furthermore, when INT3_bar senses a low pulse because a power button is being pushed on, it urges the internal signal "Interrupt request level judgment" to reset the SR latch register, which re-enables any clock oscillator, as seen in figures 1.11.9 (Maskable interrupts priorities (peripheral I/O interrupts)) and 1.10.3 (Clock generating circuit). The PMU microcontroller can resume its operations and look for the source of the interruption. It finds out it has to power up the iMac, because INT3_bar had been latched in as active.
h1. 6. Recommended updates before using the PMU Hardware Patch
+Mac OS 9: Available Updates+
http://support.apple.com/kb/HT1387
+Power PC-based iMac: When to install available updates+
http://support.apple.com/kb/HT2560?viewlocale=enUS&locale=enUS
+iMac: How to Install an iMac Firmware Update+
http://support.apple.com/kb/HT2561
h1. 7. User's Manual of the PMU microcontroller
http://documentation.renesas.com/eng/products/mpumcu/62aeum.pdf
h1. 8. Datasheets of the 74HC4049 Hex inverting high-to-low level shifter
http://www.nxp.com/documents/datasheet/74HC4049CNV.pdf
http://www.st.com/stonline/products/literature/ds/1965/m74hc4049.pdf
http://www.ti.com/lit/gpn/cd74hc4049
http://www.fairchildsemi.com/ds/MM/MM74HC4049.pdf
h1. 9. Datasheets of the 74HC193 Presettable synchronous 4-bit binary up/down counter
http://www.nxp.com/documents/datasheet/74HCHCT193.pdf
http://www.ti.com/lit/gpn/cd74hc193
h1. 10. Errata to the discussion start of February 6th, 2010
1. "PRAM battery": Wrong naming! The Logic-Board battery only serves to support the timekeeping operation when the mains is removed from the computer, whereas the PRAM data are stored in the non-volatile FLASH memory of the PMU microcontroller (in slot-loading iMacs).
2. "(...) sets bit 1 of the CM1 register (system clock control register 1) to 1 (...)". This fragment shall rather read: "(...) sets bit 0 of the CM1 register (system clock control register 1) to 1 (...)".
Aegidius_2
Keep perseverance and reach your goal!

Macbook Pro (Mid 2012 Version) refuses to power on

Hello Everybody
I have some problem here and I was hoping for some help!
Problem: Macbook Pro refuses to power on. ( no fan sound, no hard disk spinning sound)
Event leading up to problem: I was using the laptop when it suddenly it just blanked out( Power went off ). I pressed the power button and the computer started; however, after loading the operating system ( I managed to log in to the OS and was navigating my desktop), the computer blanked out again. Ever since then, the Macbook Pro refused to power on.
Solutions I have tried:
Plug in a new Magsafe Charger : I plugged in a new macbook pro charger which is working ( i verified that its working by plugging it into another macbook). The charging indicator refused to light up even when the working charger is plugged into the macbook pro.
Tried a SMC reset : I tried a SMC reset by pressing left control, left option, left shift and power button and releasing it all together. Nothing changed.
Final Note:
My macbook is out of warranty already so I am prepared to open up the laptop to disconnect and reconnect the battery, or do anything you guys might suggest;
that said, please do not advise me to bring this into a service centre. That will obviously be my final resort. We wouldn't be talking here if we could just bring it to the service centre right?
Thanks for all the help that i might receive guys !

When did it happen? After updating/upgrading? or just randomly?
You can try to perform a SMC reset and resetting the PRAM:
SMC Reset -> http://support.apple.com/kb/HT3964
PRAM/NVRAM -> http://support.apple.com/kb/ht1379

I was transferring data from my old iMac to my new iMac via Time Machine. After about 4 hours, the electrical power fluctuated and turned off my wi-fi. Now most of my necessary programs are useless. How do I erase and start over?

I was transferring data from my old iMac to my new iMac via Time Machine. After about 4 hours, the electrical power fluctuated and turned off my wi-fi. Now most of my necessary programs are useless. How do I erase that mess and start over?

Hello there, LynnS.
The following Knowledge Base article and it's referenced link should get you started with the Erase and Install of Mavericks:
OS X Mavericks: Erase and reinstall OS X
http://support.apple.com/kb/PH14243
Once you've gone through those 2 articles, this article should help you with restoring from your Time Machine Backup:
OS X Mavericks: Recover your entire system
http://support.apple.com/kb/PH14185
Thanks for reaching out to Apple Support Communities.
Cheers,
Pedro.

My screen on my 24" iMac flickers as if the power is flickering.

My screen on my 24" iMac flickers as if the power is flickering then appears to be frozen and it only happens when I'm online. This is a new issue? Any reason why this may be happening? I'm running 10.5.8 and this has never happened until recent. Could my power strip be failing? I hope nothing is wrong with the computer itself. it's only 2.5 years old.

seems to only happen when I am charging my phone on it. I recently updated to a smartphone. Could that be the issue? Maybe not charge my phone with my computer? I hope someone can help.

Where can i buy a new power lead for my iMac?

I've been looking to purchase a 2nd power cable for my iMac (the proper apple molded one with UK plug) but can't seem to find where I'd buy one. Anyone?

GENUINE APPLE IMAC POWER CABLE: Amazon.co.uk: Computers & Accessories

My Lumia 920 frequently refuse to power on

I have had d phone for up to 12 months. Although a good phone, I experience frequent refusal to power on. This requires taking it to Nokia care almost on monthly basis. I use only Nokia chargers, & don't allow the battery to drain b4 charging. What can I do.

Looks like a hardware issue, unfortunately. It is surprising that Nokia Care wasn't able to help, but i would be looking at a faulty battery, or battery connector.

Power Consumption for iMac 20" INTEL DUO CORE

I need to know which is the power consumption for the 20" 2.16 GHz INTEL CORE DUO. I want to buy a UPS for this machine and I could not figure out in any place within the manual where to get that information. It is something that have to be very easy to find but it was not the case for me in this opportunity.
I cannot believe that I have to create a post in order to get this answer!
Kind regards to all and thanks for any clue that any one can give me.
iMAC 2.16 Dual CORE 20" Mac OS X (10.4.8)

Welcome to the discussions!
Another vote for APC. I use the XS900 for my first gen G5 iMac and it works very nicely without their PowerChute software. It even comes with the correct USB cable to hook it into your Mac.

HP G62-144DX Refuses to power on

Hi
I have the same model G62-144DX notebook with a similar problem (refuses to power on) although I have no lights whatsoever and was hoping you could help! I'm looking for the RTC battery, so I can remove it and reset the unit, but can't find it. The owner's manual shows it on page 51 under the RAM, but the only thing I see is a small can (appears to be a capacitor) with #
9M3
390
2.5v.
Can you help?
Thanks!

There are 2 service manuals on the page for your model, strange, one says under the bottom cover, the other says remove the main board.
http://h10025.www1.hp.com/ewfrf/wc/manualCategory?cc=us&dlc=en&lang=en&lc=en&product=4150156&task=&

Can I buy iMac power cables for the UK?

I am moving to the UK from the US and I have several Apple products. I would like to know if I can buy a replacement cable for each of them (iMac, MacBook Pro, Apple TV, MacBook Air) that will fit into a UK power plug. All are fairly recent purchases (less than 2 years old) and I don't want to replace them. I can fit the World converter plugs on my Ipod and iPhone chargers, but they wont fit on the laptop chargers.
Thanks!
john olson | mandeville, la

All you need is an UK IEC power cord for the iMac (see image) and adapters for the Macbooks and the Apple TV.
The power supply in iMacs, Macbooks and Apple TV is an auto switching power supply that will accept voltage between 100 and 240V
Any standard european IEC power cord will do, you do not have to by one from Apple, but the Apple one as a extra round plastic part that will fit snugly in the iMac. (see second image)
Using a adapter is also an option for the iMac, but they tend to fit loosely on the US plug and can be more easily disconnected than a real European cord. If you go with only adapters, make sure you get good ones that will fit tightly on the us plug.

Power Supply for 20" g5 iMac

I have a first gen 20" G5 iMac, but it needs a power supply. Can I use a power supply from a first gen 17" model. I actually have one of those available. Thanks.

Hey Bennett,
Well power wise the two supplies are very similar.
The 20":
+3.3 V 4A
+5.1 V 9.8A
+12.0 V 6.5A
+24.0 V or +20.0Vs 0.4A
+5.1 Vsb 1.5 A
The 17":
+3.3 V 3.1A
+5.1 V 9.6A
+12.0 V 9.2A
+24.0 Vsb 0.33A
+5.1 Vsb 1.5 A
However in terms of an exact replacement, physically the differences between the two is the placement of the AC inlet socket. In the 20" it's near the right edge. In the 17" it's ~ 1" to the Left. So the locking tab indent and the socket are in the wrong place.
I think the pinouts are identical so you should be able to electrically test the 20" but you'll never get the back on without major mods.
I'd refer to Jim's site:
http://jimwarholic.com/2008/11/apple-imac-g5-power-supply-issues-and.php
He's very responsive and knowledgeable about these power supplies and you could ask him about the swap.
There are also ATX hacks to replace the 20" supply (there are many links and pics on Jim's site) and I've done that and have used the hacked ATX supplies to verify that I have a PSU problem. I've never gotten the sleep function to work properly tho'.
Richard
Message was edited by: spudnuty

Buying a new iMac... how much power do I need to run GarageBand well?

Hi All
I am about to get a 27" iMac but am weighing up the options for the processor and memory (and maybe hard drive too). Neither my wife nor I are into gaming or high end graphics stuff, so we do not need an i7 with 16GB ram... but is the bassline 27" iMac powerful enough to run GarageBand with no problems?
I have not really used it much before as our laptop is about 6 years old and it really struggles running GB, hence I have not been keen. However as I am a musician and am about to get a new computer... I am keen to find out just how much power I'll need.
At this stage, I want to play around with GB and dop some aranging, not sure how many tracks this will end up equating to as my experience grows... but unless I really get into it, I am unlikely to progress to Logic or similar... but if I did, would I need more than the baseline?
So in short... do you guys think the 27" iMac i3 with 4GB RAM will cut it for someone who is getting started but wants to spend a reasonable amount of time in GB? Why/why not?
Thanks

TuningPeg wrote:
In order to fully understand what you just said to me... I had better find out what an 'Addictive Drum AU' is. I am quite teh newbie when it comes to digitally recording, either from a real instrument or a virtual one.
I am assuming that the Addictive Drum is fairly intense when it comes to the CPU? Are there many other virtual instruments that are hard on the CPU? For an average user I am assuming this will not pop up to often, correct?
Garageband is not a 'closed system' in that you are stuck with what it offers. You have the option to use 3rd party software to enhance your productions. AU stands for Audio Unit, a coding standard around which many 3rd party developers use to integrate with Mac products. As you develop your own habits and tastes with your productions, you might decide that the options GB offers you are not to your liking. This is where these sorts of products come in. They are very easy to use with GB. Addictive Drums is a Drum program that is actually lightweight on your system compared to others. The only reason I had 8 instances (one loaded on 8 individual MIDI tracks) was because of a limitation GB has. It suited my workflow to do it this way.
There is a huge range of AU's available, Native Instruments being a company that does a very good set of products. Some are indeed very CPU intensive, others are not. You have to do your research by asking questions on various forums and seeking reviews etc.
The term 'Average User' really means nothing in my honest opinion. Depending on your preferred genre of music and how you go about hooking into this slippery slope of hobby home recording, you may bump into a variety of limitations either in GB itself or limitations because of your machine. Because RAM is easily replaced by the owner and hard drives are easily obtained for extra storage, CPU is the thing your are stuck with from day one. Programs are getting bigger and they are relying on lots of number crunching. Amp simulations are a good example of CPU intensive software. It is easy to find yourself spending $60 here and $99 there on all sorts of cool Software, and before you know it you have quite the quiver full. I am not a heavy GB user, in that I don't run 30+ tracks on my projects. I am a 12-16 track average user most of the time. However, the reason I upgraded to my iMac recently was because I had one piano AU, yes just one, that stopped my 2 year old macbook in its tracks when using another recording program. I had all the RAM that GB could use, an excellent hard drive and a very good sound card, but the computers lack of grunt made working with it tedious and sometimes frustrating. You more than likely have a budget to work with when getting your machine. The advice I would give any personal friend who was getting their first computer for recording is to get the most CPU you can for your budget. You could be staring at this machine for the next 4-6 years. Typically RAM and hard drives get cheaper over time should you need them, relatively small prices to pay in the long run.

Place to purchase 2cd power cord for iSight iMac?

Anyone know where I can buy a second power cord for a 17" iSight iMac? I've been searching the web but no luck yet.
Why would I need one? My new iSight iMac is going to live in a computer cabinet in front of a difficult to access wall outlet/power strip. I'd like to be able to move the computer around the house to watch DVDs in comfort (hurray for Front Row!), and a second power cord will make this transition a lot easier.
Thanks in advance for any suggestions.

How fussed are you about aesthetics? Have a dead electric jug or kettle or stereo amp at home? See if the cord fits.
Cheers
Rod

Which iMac usb port is high power?

Which iMac USB port is high power?

I'm not sure this is the case, at least on the newer iMacs. Some ports will adequately power some devices (most notable the USB Suerdrive) while others won't. Or, this has been the case recently, anyway; USB with Apple devices seems hopelessly arcane anyway, which makes no sense at all!)

Zombie iMac 21.5": refuses to power on for hours

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