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The iMac G3 came in tangerine, blueberry, lime, grape, and strawberry colors.

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Powers up (can hear hi-voltage), No Sound, No Picture

Can not see CRT filaments. Resistance of filaments is low. Computer MB has all the correct voltages, processor gets hot. Power supplies seem good with the exception of the +130v is only 87volts. I don't know if that's normal if the computer is not turning the display on? Or might the Power Supply board have a problem, or the CRT Board? Do the speakers hook up from the CRT Board via that video cable or how do the speakers get their sound? This thing does not bleep, bloop or do a thing. LED stays orange,

Ответ на этот вопрос У меня та же проблема

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@daveyk021 since you don't get any sound or picture, this appears to be an issue with the power supply (PAV board which stands for Power, Analog, Video). Be forewarned, it's a bit of a PITA to work on ;-). Of course, it's a CRT so you want to be extra careful since you will need to discharge the CRT and not getting zapped on it. It'll bite pretty good, so unless you are familiar with CRT's, I'd get somebody to help with that first. Here is a good guide for the replacement iMac G3 Model M4984 Power Supply Replacement and here is a decent document G3 Disassembly

Now, to work on the CRT use the Apple safety guide ESD Safety Guide After you get to your power supply, take some really good pictures and post those with your Question. That way we can see what you see.

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Update (11/04/23)

No power. System is completely dead. No LED, no fan, no hard drive power, and the screen is completely black.

Verify the power outlet is good. Try a known-good power cord to determine if the existing power cord could be the problem.

Possible bad USB keyboard. Verify the keyboard cable is connected properly to the computer.Disconnect the keyboard and power on the system via the button on the front of the computer. Do you have power to the system now?

  • Yes: The keyboard is bad. Replace the keyboard.
  • No: Go to next step.

Reset the CUDA chip and try again. If the problem persists, reset the logic board. (See “The CUDA Chip” and “Restarting the Logic Board” earlier in this chapter for instructions.) Do you have power to the system now?

  • Yes: Run diagnostics.
  • No: Go to next step.

Possible bad logic board or power/headphone board. Check for trickle power on the logic board. Is there +5V power?

  • Yes: Replace the logic board. If problem persists, replace the power/headphone board.
  • No: Check for trickle power at the power supply to power filter cable. Is there +5V power?
    • Yes: Replace the logic board. If problem persists, replace the power filter board.
    • No: Go to next step.

Possible bad power supply to power filter board cable. Check for trickle power at the power supply board. Is there +5V power?

  • Yes: Replace the power supply to power filter cable.
  • No: Go to next step.

Possible bad power supply board. Replace the power supply board

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. Press the Cuda reset button on the logic board to reset the Cuda chip. (The Cuda reset button is located on the back edge of the logic board between the modem port and the processor module.

iMac G3 Model M4984 Power Supply Изображение


iMac G3 Model M4984 Power Supply Replacement



15 minutes - 1 hour

iFixit Изображение


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Очень просто

2 - 5 minutes

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The whole reason I wrote that guide all these years ago is that my PAV board also died in my G3. Symptoms were mostly as described, no video but the computer sounded "on". If I recall correctly, the power LED would turn on when pressed, stay on for a short while while the computer made sound, then the LED / sound shut off.


Thank you. The MB has all the correct voltages, +5, -5, +/-12volts. The processor gets fairly hot. I think there is still an issue with the CRT and/or power supply board as the +130 is only 87volts. Still no bleeps, bloops or anything out of the computer portion.

No CRT filaments lighting (filaments look okay on ohm meter). I just know if that section turns on if the computer doesn't work?

Right now without any sound out of the computer, why worry about the display? Computer wise, battery is pulled; it is 100% dead. I may have new batteries tomorrow from Amazon. I did the power management reset; still dead (no sound); LED stays orange.


@chrisgreen P.S. - To work on the PS Board, can it run when removed from the chassis? Would there not be a jumper or the stand by voltage looped back to turn it on?


@daveyk021 we'll need to find out if it requires something like a pull-up or pull-down resistor to turn it on. Let's see if there are any schematics for it. Quick Question, for you, does this model have the VGA port on the bottom?


@oldturkey03 I worked on the PS for some time. I finally found the switching transistor that when the E-C close/shorted allowed the 130v to go from about 78volts to 130 volts. Then on the CRT board, I found the switching transistor that turns the filaments on (I bypassed it), then found many other circuits not enabled.

So, I think it is the computer not booting preventing the CRT from coming on.

I sat it aside and grabbed my other iMac G3, it booted the first time. I found out it has licenses office (1998 - lol). Once finished playing around, I told the OS to shut down. That's the last time it booted - lol. Chimes/Green light and then shuts down. <sigh>. At least this one chimes. The original one I started this thread about does not chime (if speakers are okay).


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Okay, I have one working out of two. I replaced the flyback with one from the donor. It worked! But the un-blanking pulse had a lot of ringing and I would get vertical strips if the Screens were turned up too high. I did buy a brand new 6174Z-1003G flyback for about $100, and it fix it and the display now works perfect.

CD Drive didn't work at all. Replaced it with one from the donor. I have written three 9.2.2 ISO disks from two different machines. I've only managed to get 9.2.2 "mostly" installed with CD read errors. The first two I burned was on my Windows 11 machine with a Blue Ray/DVD/CD burner. So then I tried my industrial chassis with just an old DVD burner. That didn't work as well.

I do have another (used) 24x CD drive on order from EBAY. I will find out if it's any good. In the meantime, I want to install an old just CD burner in one of my machines. My Windows 11 Gaming system is in a Pop-Air case and can hold two optical drives (that is why I bought that case). So I will probably install an old CD Burner in it to try. I will also try another brand of blank CD-R.

This is really been a pain in the ASxx. lol

I also need to align the convergence. I have a great convergence JPEG file, that would display under the old 9.1 system, but I cannot get to display under the 9.2.2 that I managed to install on to an SSD. What does it take to display a JPEG on these systems? I am thinking that part of the OS did not install due to read errors with the CD drive (yes, I did tear it apart, manually clean it and grease the worm gear and slides). Is there a program I could install to get it to show JPEG files?

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