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toples50

iMac G3 black screen

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I have purchase after a long time a rev.A iMac.First time boots ok and then nothing.It starts with a chime the disk spinning for while but the screen is black and the machine remains stuck.Any suggestions please?(this is the first time I have received an iMac in such a great external quality and without broken parts)

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Check the service manual, I believe this machine may have an internal battery. I know that my iMac G3 333Mhz model had a blown battery, it had a similar symptom, checking it I discovered a leaked battery. In my case I had to replace the logic board (the daughter card was ok)

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Thanks guys its very hard nowadays to find a working condition Rev. A iMac.I don't want know if it's worth it to fix it or to open a claim against the seller. 

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Quote

hook up a vga monitor and see if u get picture

 

yes, good point, the Imac has a video connector on the logic board side, hooking a Macintosh screen is a really good idea.

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Only some of the slot-loading iMacs had the external VGA port. The tray-loading ones used the older connector and can work with older Macintosh displays.

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I would try the following if you hear a startup chime, the LED lights up and you hear the HD spin up.

 

Try in this order:

Reset PRAM (if you do hear a startup chime when powering up but you can't reset PRAM the kbd might be bad, try another keyboard or USB port - you can test if kbd is problematic by turning computer on from keyboard)

Boot off CD

Press the PMU on the logic board with the AC power disconnected from the computer.

Verify that the CRT video cables and the deflection yoke cable are securely attached.

Check for bent CRT neck pins, remove the CRT video board and check that the pins are not bent and that they are clean, use isopropyl alcohol to clean them.

 

For PMU reset, I strongly suggest you find the service manual for your machine, it has very good information on symptoms and steps to take. The PMU is VERY sensitive and can crash causing batteries that last five years to die on 2 days.

 

PMU reset

Disconnect Mac from power.

Battery should read between 3.3 and 3.7 volts. If bat is bad replace it and wait 10 seconds after replacing before continuing with PMU reset.

Press the PMU when a known battery is installed (press only once as it can crash the PMU - it's sensitive)

after PMU is pressed (once) wait 10 seconds before applying the power cord and powering up the computer.

If a PMU reset doesn't revive the machine as expected, something else is wrong.

 

 

Again, I highly recommend you find the service manual for your iMac, sit down with a tea or coffee and review the symptom chart section. All the info was paraphrased from the manual. Copy and paster wasn't working for me, I don't know why but I hope this steps help for now.

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Thanks for the guide.I have try it but still nothing.The iMac does not boot.Just the HDD spins up for a while but the screen is black and the power button is somehow orange.

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No video, the screen is either completely black, or you will see horizontal rolling lines. There will be power to the system, however, which is evidenced by an illuminated amber LED, and a running fan.

 


1. Reset parameter RAM. Hold down <Command> <Option> <P> <R> during startup but before “Welcome to Macintosh” appears.
2 Reset the CUDA chip and try again. If the problem persists, reset the logic board. (See “The CUDA Chip” and “Resetting the Logic Board” earlier in this chapter for instructions.)
3 Do you hear a normal boot chime at startup? Yes: Go to next step.
No: Follow these steps to resolve the problem:

1. Reseat the SDRAM.
2. Reseat the processor module.
3. Replace the processor module.
4. Replace the logic board.

 

4 Verify that the following cables are attached securely:
• Internal RGB cable that attaches to the A/V interconnect board at J5.
• Internal video cable that attaches to the logic board at J16 and the A/V interconnect board at J2.
• Internal RGB cable that attaches to the video portion of the analog/video board at board at P301.

 

5 Replace the analog/video board. Exchange like-for-like, there are two versions of the board.
6 Replace the internal video cable that attaches to the logic board at J16 and the A/V interconnect board at J2.
7 Replace the A/V interconnect board.
8 Replace the logic board.
9 Replace the internal RGB cable that connects at the A/V
interconnect board at J5 and the analog/video board at P301. 1 0 Replace the CRT.

 

image.png.56c0d531649396905e22010d61999dce.png

 

The Cuda Chip

The Cuda is a microcontroller chip. Its function is to:

  • Turn system power on and off.

  • Manage system resets from various commands.

  • Maintain parameter RAM (PRAM).

  • Manage the real-time clock.

    Many system problems can be resolved by resetting the Cuda chip

 

 

Resetting the Logic Board

Resetting 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. Unplug the computer.

  2. Disconnect the cable that runs from the power supply to the power filter board on the bottom side of the logic board/mass storage chassis.

  3. Press the Power On button on the front of the unit.

  4. Remove the logic board/mass storage chassis from the unit.

  5. Remove the battery from the logic board.

  6. Wait at least 10 minutes before replacing the battery.

  7. Make sure the battery is installed in the correct +/- direction.

  8. Reassemble the computer and test the unit.

Note: This procedure resets the computer’s PRAM. Be sure to check the computer’s time/date and other system parameter settings afterwards.

 

When handing the logic board where an antistatic wrist strap. When handling the CRT do not wear antistatic wrist strap. Take off jewelry and don't wear clothing that can hold a charge such as synthetics when doing either the CRT or logic board handling. Be careful with the CRT.

 

I included a caption of the iMac Hot Issues.pdf Page 85-95. Maybe you can find this pdf online.

iMac Hot Issues (2001).pdf

Edited by Alex

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I'm not sure but I think is the Flyback transformer the problem.

Machine power ups hard disk spins for a while and then the machine stays with black screen...

I have opened it I'v changed battery reset the cud but still nothing.

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If you refer to my notes further up, there are steps that call fro reseating some components, RAM and CPU card etc. Did you perform those? I highly recommend you refer to the service manual when performing the reseat operations as there are other steps surrounding it. You say still nothing but there are other steps that you've not announced as completed, please check all steps. First we need to make sure all steps are performed before someone can help to narrow down to component failure.

Edited by Alex

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I have reseat all the components but still nothing.Unfortunately I'm not a technician I don't have a volt meter.I have done the basics stuff only.

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I hope someone else can contribute to some theories on what steps to perform next. I wish I could help you a little further. Please keep us posted.

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