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iteachmac
iteachmac, The Duke!
Category: Mac
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Experience:  Mac help ,music midi expert, logic pro recording ,electrical installation ,ilife & all mac computing
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Hello I have an Imac model m5521(M8582LL/A) Indigo/snow 500MHZ

Customer Question

Hello
I have an Imac model m5521(M8582LL/A) Indigo/snow 500MHZ slot load that will not turn on. I am an electronic tech that services to component level. I need to get a schematic or a npartial schematic of the power supply to the down/converter board, or information on the power flow from the input AC plug to the output of the down/converter board.b
Submitted: 3 years ago.
Category: Mac
Expert:  iteachmac replied 3 years ago.

iteachmac :

hi , you will have to do some reading here but this guide may help . internal battery change and reset may help.

iteachmac :

and :

iteachmac :

do you get chime while powering on ?

iteachmac :

do you get apple logo ?

iteachmac :

Resetting the pram , after battery replacement can help .

iteachmac :

Please follow the full guide for your Mac :-
http://support.apple.com/kb/HT1379?viewlocale=en_US

extra info :-

Contents of PRAM

Some Macintosh computers may not have all the settings described below.

Settings Stored in PRAM :-

Status of AppleTalk
Serial Port Configuration and Port definition
Alarm clock setting
Application font
Serial printer location
Autokey rate
Autokey delay
Speaker volume
Attention (beep) sound
Double-click time
Caret blink time (insertion point rate)
Mouse scaling (mouse speed)
Startup disk
Menu blink count
Monitor depth
32-bit addressing
Virtual memory
RAM disk
Disk cache

Ok, let me know if this helps ?


Thanks.

Customer :

Also have no "Trickle Voltage on the Logic Board Test Point

iteachmac :

Iv heard the APV board or Down Converter Board are the main issues on the board for failing .

iteachmac :

Do to overheating .

iteachmac :

due .

iteachmac :

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iteachmac :

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iteachmac :

this guide shows a full tear down of imac models and gives some info for part numbers .

iteachmac :

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iteachmac :

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iteachmac :
Power Flow
Troubleshooting
Power is controlled in the iMac system by the power/analog

board. Once the unit is plugged in, power flows from the AC outlet at the wall to the AC inlet on the power/analog board. From there, the power flows through the main cable on the power/analog

board, to the video neck board, down converter board, logic board,
and all its attached components.
iteachmac :
Testing for Power
Troubleshooting

The iMac requires trickle voltage (+5 TRKL) in order to power- on. If you are experiencing power problems in the iMac unit, you will want to test for trickle power to pinpoint the location of the problem and to determine whether or not the power supply/analog board is functioning normally. If you have trickle power in the

system, the odds are your power/analog board is OK.
In general, you should test for power at the AC outlet first. Next, it
is best to check the logic board. In this way, you will be able to
immediately pinpoint which module is failing.
The following procedures will explain how to test for power at the
AC outlet and at the logic board.
iteachmac :
At the AC Outlet
If the unit will not power up from the keyboard, first, unplug the
keyboard from the computer. Then, using a known-good power

cord, power-on the system using the power button on the front of the computer. If the system powers on, you can assume the AC out- let is good and the problem is with the keyboard. If the system still won’t power on, try connecting to a different AC outlet. If the unit powers on this time, you most likely have a problem with the AC outlet. If you still have no power, you may need to reset the PMU chip (power manager) on the logic board (refer to “Resetting the Logic Board” in this chapter).

iteachmac :

-

iteachmac :
At the Logic Board
With the iMac placed with the CRT face down on a soft surface,
remove the bottom housing and the EMI cover to access the logic
board.
Testing J9 for +5 V Trickle Power on the Logic Board
You will need a volt meter to test for power on the logic board.
Refer to the picture on the next page to locate the necessary test
point referenced in the following procedure.

Plug in the computer, but leave the iMac powered OFF. Ground the black probe on the volt meter to the logic board screw, as shown in the photograph below. With one hand behind your back, touch the red probe on the volt meter to the top pad (pin 1) at J9 (see the photograph below) on the logic board, to see if you have +5V on the logic board. A +5V reading on the logic board means the power supply is providing the necessary trickle voltage to the logic

board.
iteachmac :

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iteachmac :

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iteachmac :

Testing for +5 V Trickle Power at J9 on the Logic Board

iteachmac :
Testing DCO (Down Converter On) Voltage at C10 on the Logic
Board
In a No Power situation, first check for +5 V trickle power at J9
(refer to “Testing J9 for +5 V Trickle Power on the Logic
Board”), then check the DCO (Down Converter On) voltage on the
logic board at capacitor C10 (see figure below).
The DCO voltage should be present as soon as the power cord is
plugged into the computer. Ground the black probe on the volt

meter to the logic board screw, as shown in the photograph below. Touch the red probe to C10 (see the photograph below.) The DCO voltage should measure approximately -1.2 volts with the power cord plug plugged in. The voltage will jump to 21 volts after pow- ering on the system. A reading of -1.2 volts up to +1 volt indi- cates the logic board is OK. Without a reading of -1.2 volts, verify the fuse at F901 is OK (refer to “Testing the Power/Analog Board Fuse” in this section). If the fuse is OK replace the power/analog/ video board.

iteachmac :

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iteachmac :

Testing J7 for Voltage on the Logic Board

The following voltages measure if the down converter is providing
the required voltages and are only present if the system is pow-
ered on. If the following voltages are not correct, refer to the “No
Power” troubleshooting symptom chart.
Measure the following voltages at J7 on the logic board:
1.
Pin 2: +12 volts
2.
Pin 4: +5 volts
3.
Pin 14: +3.3 volts
iteachmac :

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iteachmac :

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iteachmac :
- Testing the Power/Analog Board Fuse
First remove the bottom housing, front outer bezel, and the top
rear housing to access the power/analog board. The fuse is located
near the AC plug.
Warning: You must unplug the iMac to do a continuity test at the
power supply board fuse.
You will need an ohm meter to do a continuity test on the power
supply board fuse. Refer to the picture below to located the neces-
sary test point referenced in the following procedure.
Unplug the computer to take this reading. Using an ohm meter,

touch the red and black probes to the two metal points at location F901 and check for continuity (reading of “0”). If the ohm meter registers “0”, the fuse is good. If the meter registers “infinite”, the power/analog/video board should be replaced. A bad fuse is

indicative to a power/analog/video board problem.Note:To take
this reading, it’s easiest to insert the red probe of the meter
through the opening on the back side panel.
Testing Fuse 901 for Continuity
iteachmac :

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iteachmac :

-

iteachmac :
The PMU Chip
Troubleshooting
The PMU (Power Management Unit) is a microcontroller chip that
controls all power functions for the computer. The PMU is a
computer within a computer. It has memory, software, firmware,
I/O, two crystals, and a CPU. Its function is to:
• Tell the computer to turn on, turn off, sleep, wake, idle, etc.
• Manage system resets from various commands.
• Maintain parameter RAM (PRAM).
• Manage the real-time clock.
Important:Be very careful when handling the main logic board.
Remove the battery when handling the logic board so the PMU is

not affected. The PMU isvery sensitive and touching the circuitry on the logic board can cause the PMU to crash. If the PMU crashes, the battery life goes from about five years to about two days if the PMU is not reset. Refer to the next topic, “Resetting the PMU on the Logic Board” for the procedure. Many system problems can be resolved by resetting the PMU chip. The PMU reset button is

located on the right side of the board, refer to the logic board dia-
gram below.
iteachmac :

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iteachmac :
Resetting the PMU on the Logic Board
Troubleshooting
Resetting the PMU (Power Management Unit) on the logic board
can resolve many system problems. Whenever you have a unit that
fails to power up, you should follow this procedure before
replacing any modules.

1. Disconnect the power cord and check the battery in the bat- tery holder (BT1). The battery should read 3.3 to 3.7 volts. If the battery is bad, replace the battery, wait ten seconds, and then reset the PMU (refer to the next step). If the bat- tery is good, go to the next step.

2. Press the PMU reset switch (S1) once on the logic board and then proceed to step 3. DoNOT press the PMU reset switch a second time because it could crash the PMU chip.

3. WAIT ten seconds before connecting the power cord and pow-

ering the computer on. If the computer powers on, go to the next step. If the computer does not power on, there is some- thing else wrong with the computer, refer to the symptom/ cure chart, “No Power” in this chapter.

4. Run MacTest Pro and return the computer to the customer.
Note: This entire procedure resets the computer’s PRAM. Be sure
to reset the computer’s time, date and other system parameter
settings before returning the computer to the customer.
iteachmac :

-

iteachmac :
Power-On Self Test
Troubleshooting
There is a power-on self test that resides in the ROM of the iMac.
This test automatically runs whenever the iMac is powered on
after being fully shut down (the power-on self test does not run if
the machine is only restarted).
If a problem is detected during the test, you will not hear a normal

startup chime. Instead, the system will beep as explained below. Refer to “Error Beeps” later in this chapter for instructions on how to troubleshoot and repair an iMac that sounds error beeps at startup time.

Following is a definition of what the error beeps at startup time
signify.
One Beep:No RAM is installed or detected.
Two Beeps: Incompatible memory is installed. (The iMac
ships with PC-100 SDRAM and does not accept SDRAM SO-
DIMMs or EDO memory).
Three Beeps: No RAM banks passed memory testing.
Four or Five Beeps: Bad checksum for the remainder of the
boot ROM. The ROM (which is located on the processor module)
is bad.
iteachmac :

-

iteachmac :
Logic Board Battery
Troubleshooting
Important:Apple highly recommends removing the battery when
handling the logic board. Make sure to use proper ESD protection
when handling modules.

The battery on the logic board controls the stored system settings, such as date and time. It is only necessary to test the battery when you can’t power on the computer, or the date and time are reset every time the AC power is removed.

The battery is also used to power the PMU chip (because the PMU chip keeps time and must always be running) when the computer is unplugged from the wall (AC power). The PMU isverys e n s i t i v e and touching any circuitry that is connected to the PMU can cause it to crash. If the PMU crashes, the battery life goes from about five years to about two days if the PMU is not reset. Once the bat- tery goes dead, the PMU will reset the time and date to 12:00 AM 1/1/04 every time the AC power is removed. To fix this situa- tion, replace the battery and reset the PMU (refer to “Resetting the PMU on the Logic Board” mentioned earlier in this chapter).

If the computer has a “No Power” situation, check the battery
before replacing modules. When checking the battery, make sure
the computer is unplugged. Measure the voltage across the bat-
tery’s BT1 positive and ground terminals. The battery should read
3.3 volts to 3.7 volts. If it’s lower than 3.2 volts, replace the
battery and reset the PMU chip.
Note: The iMac uses a lithium battery that must be disposed of in
accordance with hazardous waste regulations.
iteachmac :
Power/Analog/Video Board Switch
Exploded View
5

There are two part numbers in service stock for the power/analog/video board on the iMac DV computers (Summer 2000) because there are two vendors manufacturing the boards. The part numbers are XXX-XXXX and XXX-XXXX. These boards must be exchanged like- for-like.

The XXX-XXXX board (Figure 1) has a switch at location SW901 that must be set for the type of CRT tube in the computer. The switch settings are silk-screened on the board near SW901. If this power/analog/video board or the CRT are replaced, make sure to set the switch to the appropriate position (either to LG or CPT). Refer to the next page for CRT identification information.

Figure 1 Power/Analog/Video Board XXX-XXXX
iteachmac :

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iteachmac :

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iteachmac :

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iteachmac :

spare part :

iteachmac : Apple iMac G3 Power Analog LG Video board 6870T194A11
iteachmac :

more spares :

iteachmac :

Hi , hope all thia info is of use to you ,

iteachmac :

If you need more info , you may be able to contact apple , or a service provider .

iteachmac :

alternatively you may be able to get extra help via :

iteachmac :

Thanks.

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