Need help with iMac G3 400 DV - Newbie here!.

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Level 1

10 points

Need help with iMac G3 400 DV - Newbie here!.

Hi to all. This is my first post. I'm a totally Mac newbie, but I have very good experience at computer repairment.
A friend of mine was about to trash his iMac. So I asked him to give it to me.
The computer doesn't start up. I'll try to explain the problem (sorry for my english).
When you press the power button, it lits up green, hdd starts to spin and nothing more happens, no chimes, no video, nothing.
If I uninstall the mem dimm, and power it up it will make one beep. According to repair manual, this is normal, one beep=no ram.
I've changed the memory just to make sure dimm was dead. I've tried 10 100/133 dimms, and the same happens, with memory inserted nothing happens. Without mem I hear one beep.
So I've opened it up. Checked everything that the repair manual suggests.
Battery is good (3,6 v)
+5V TRCKL is present
C10 shows -1.2 Volts. (it jumps up to 23V when powered on)
+12V, +5V and +3.3V is present at DCO connector.

Any suggestions?

Thanks a lot in advance.

iMac G3 400 DV, Mac OS 9.2.x

Posted on Sep 12, 2007 7:23 AM

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Answer 1

Sep 12, 2007 7:41 AM in response to DSpawnZ

WELCOME...

But, past the DCO??

This is the second iMac G3 400 DV with the same problem here,
see here:
http://discussions.apple.com/thread.jspa?threadID=1128076&tstart=0

sounds like a logic board to me, but a DCO on eBay is only $9.95, yes, I checked it out... 🙂

but then again, sounds like a part here, a part there...
+maybe - worth the $9.95 just to see+

sorry,
den
.
.
.

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Answer 2

Sep 12, 2007 10:34 AM in response to DSpawnZ

Hello DSpawnZ,

You did not mention, but was the computer in this state when you received it? I wonder if the original owner who gave the computer to you had tried to upgrade the computer to OS X without updating the firmware? This can create a black screen/non-booting computer.

Sorry if I'm misunderstanding the problem.

littleshoulders 🙂

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Answer 3

DSpawnZ Author

Level 1

10 points

Sep 12, 2007 11:19 AM in response to DSpawnZ

Hi again.
Thanks to you all for answering.

Sadly it's almost imposible for me to buy items from ebay because of customs and shipping costs here in Argentina.
To be more specific with my problem.
DCO seems fine. A couple of minutes ago I've checked that there is a pin that is called +12S (+12V Sound) I guess this feeds power to sound amplifier. This pin has 16.4 volts. Other pins has correct values.
As far as I know, the machine was running MacOS 9.2.2 and no MacOSX update was performed.
One question: The 24 Volts AC DCO feeds from, are 24 Volts high frequency ac?

Any suggestion would be appreciated.

Cheers.

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Answer 4

spudnuty

Level 5

7,128 points

Sep 12, 2007 12:32 PM in response to DSpawnZ

Hey and welcome to the forum:
Well since you have the service manual try resetting the PMU.
I have yet to see a bad logic board or down converter on these slot iMacs. Presently I have 2 400, 2 350 boards and DCOs and 5 bodies with dead PAVs. Usually it's the flyback but often it can be the HV caps. Your symptom sounds like flyback but do the PMU reset first.
You can pull the PMU board and check the soldering on the flyback (heed the warnings about the anode voltage). I have seen 3 examples of cracked solder joints there so those were a simple repair.
My usual scheme is to drop the 400 board into a 350 since it's a direct swap. You get the faster speed and FireWire.

Richard

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Answer 5

DSpawnZ Author

Level 1

10 points

Sep 12, 2007 12:47 PM in response to DSpawnZ

Hi spudnuty. Thanks for your advice.
When I come home from work I will check que PAV board and flyback soldering.

I'll let you know what happened.

Thanks, a lot.

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Answer 6

DSpawnZ Author

Level 1

10 points

Sep 12, 2007 4:19 PM in response to DSpawnZ

I've resoldered every flyback pin just in case.
Did a PMU reset too as stated in the manual.
Same thing. imac is dead.
Which capacitors should I check?.

Thanks

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Answer 7

DSpawnZ Author

Level 1

10 points

Sep 18, 2007 3:56 PM in response to DSpawnZ

Hi to all. My problem has been solved.
I've bought a pulled out logic board for U$S 20.
iMac is working like new.

Thanks to all.

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Answer 8

spudnuty

Level 5

7,128 points

Sep 18, 2007 5:57 PM in response to DSpawnZ

So it was the logic board and not the down converter that was the problem?
Richard

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