iMac G4 Repair

[AL1630]

I have a nonfunctional 1.25Ghz/USB 2.0 17" iMac G4 that I'm trying to fix. I found the Apple service source for this model and followed the instructions to test the power supply, and it checked out. The service source said that if the Power Supply Checked out, you should replace the Logic Board, so I ordered one on eBay and it arrived today. I installed it and got everything reconnected, but it still won't start. I've replaced the PRAM battery with a tested good one, reset the PMU, and checked the cables, but those didn't do anything. There's one sign of potential life - when the machine is plugged in, I can hear a faint beeping from the internal speakers. Are there other things to test or replace?

 

[Resplendent]

Bad RAM?

 

[AL1630]

Bad RAM?

It could be that, unfortunately none of my other machines use the same type so I can't test it.

 

[bunnspecial]

It could be that, unfortunately none of my other machines use the same type so I can't test it.

Does it have one or two RAM modules installed?

If so, remove one of them.

If not, try pulling the internal module and if you can find one(it should be cheap if you don't have one) put a DDR SO-DIMM in the lower slot.

 

[AL1630]

It has 2 modules, and won't boot with either installed.

 

[AphoticD]

A few ideas:

• Disconnect HDD, optical drive, modem, and any other internal components to see if it powers on
• Disconnect the internal speakers, plug in some headphones and try again
• Remove the logic board and possibly the PSU from the chassis and see if you can boot it outside of the case.
• Disconnect the power button and manually jump the pins with a screwdriver to see if the power button is at fault.

Any other thoughts to isolate the issue?

Sometimes a simple short in any of the circuits (even in a device like the speakers) can cause things to appear completely dead.

 

[AL1630]

After further disassembly, I unplugged the speaker cable, and found that the beeping noise persisted and is actually coming from the PSU, seemingly both 'halves' of it. It still wouldn't power on after pulling the drives and modem. Even though the power supply passed the test, could it still be the bad component?

 

[z970]

After further disassembly, I unplugged the speaker cable, and found that the beeping noise persisted and is actually coming from the PSU, seemingly both 'halves' of it. It still wouldn't power on after pulling the drives and modem. Even though the power supply passed the test, could it still be the bad component?

It's possible.

 

[AphoticD]

After further disassembly, I unplugged the speaker cable, and found that the beeping noise persisted and is actually coming from the PSU, seemingly both 'halves' of it. It still wouldn't power on after pulling the drives and modem. Even though the power supply passed the test, could it still be the bad component?

It is possible that the PSU can provide a normal voltage reading when sitting idle, but fail to keep up under load. So yes, it’s not as common to see that, but it is theoretically possible.

Is there anyone near you with the same series iMac who could help you test your components with something known-working? It’s quite possible you now have two working logic boards.

 

[AL1630]

Unfortunately, I don't know anybody in my area with one of these, so that probably won't work. I guess I could buy a tested working PSU on eBay and sell a logic board if both work. (Still cheaper than a functional 1.25 iMac)

 

[AL1630]

Update: I got a new PSU and the fan now spins up, but there isn't any video. I tried an external monitor as well, but no luck.

 

[Resplendent]

Does it chime now?

 

[MBAir2010]

I have worked on my imacg4 a lot during the 2000’s
Recheck your connections, the screen has 2 I think
maybe tomorrow......
these computers have a lot of screws, wires and carefully assembly and positioning required for a night.

What was wrong with the old motherboard?

 

[AL1630]

OK, so I put the old motherboard back in because why not, and of course the iMac now works. Now I have to figure out what to do with the new board I ordered, since I don't even know if it works.

 

[MBAir2010]

OK, so I put the old motherboard back in because why not, and of course the iMac now works. Now I have to figure out what to do with the new board I ordered, since I don't even know if it works.

I might need one, I have a (see below) with a grey Apple screen after starting.

[doublepost=1530842058][/doublepost]Maybe you should keep one as a spare, just Incase

 

[AL1630]

Another update: I re-assembled the computer, and now it won't start. It does the same thing as before with the fan spinning but nothing else. I pulled it apart again, still nothing.

 

[CooperBox]

With the bottom housing open, perform a very detailed visual inspection for any signs of damage on the interface cables, i.e. evidence of chafing or similar as they can easily get partialy trapped and 'nipped' during re-assembly of bottom casing to the top. The start button may also have a faulty component or connection.
With housing still open, check inside each connector with a magnifier - especially the large data connector for any evidence of a pin or socket deformed or loose.

 

[AL1630]

I checked each cable and they all look good. I unplugged and re-plugged everything as well, but it still won't start. It's weird how I got it to start that one time but now can't.

 

[z970]

"Did you try repairing permissions?"

 

[CooperBox]

"Try rebooting it!"

"Qué?"