iMac G3 died

[naujoks]

I was using my iMac G3 when all of a sudden the screen went really dark and the picture got distorted. The computer was still working at that stage. A couple of minutes later the computer shut down completely. Now I can't switch it on anymore. I can hear that it's trying for a split second to switch on the high voltage but then there is nothing. No LED.
I checked for blown parts or leaky caps, but it all looks good. I'm measurin 4.87V at the trickle voltage test point J9 on the mainboard.

What could be wrong?

 

[DeltaMac]

Which iMac do you have?
The optical drive is the easiest to tell more, so... Is the optical drive tray-loading or the newer slot-loading type?

 

[naujoks]

It's the slot loading type.

 

[DeltaMac]

High-voltage has likely failed on the Power/Analog/Video (PAV) board.
That has the flyback transformer for the CRT, and is the common failure on that board. You get very distorted video, which usually goes to a vertical(?) line, if you see any video at all when the flyback has failed.

 

[naujoks]

I didn't see a vertical line, but the picture went very dark and it was distorted.
So you think the flyback has failed? Is there any something I could measure to confirm that it is faulty?

 

[DeltaMac]

Apple's service manual for your iMac has pretty good voltage tests for various failures.... Might save you a lot of time that you may need for testing. Apple's service manual downloads are not too hard to find, and can certainly help you with deciding if a part is good, or not.
There's 4 different model identifiers for the slot-loading iMacs, so it would be good to identify which exact model you have. Each model has its own distinctive service manual.

 

[doctor_dog]

Sorry to semi-necro-post here, but I've got an iMac G3 with the same issue. Ran across this write-up on how to replace the flyback transformer so you don't either have a very cool paperweight or be out lots of cash getting it fixed at a shop. Parts might be tough to find though.

Note, from what I understand this could actually end your life if you aren't careful, so please tread lightly!
https://www.moonrockreptiles.com/columns/imacrepair/index.html
https://www.moonrockreptiles.com/columns/imacrepair/index.html

 

[naujoks]

I've since repaired my iMac. It was indeed the flyback transformer that has failed. I since learned that this is the most common failure in these computers. In fact, they might all eventually die. Like all of us.
The flyback was all bloated and cracked.
New flybacks are impossible to get hold of. I found a couple of people who were selling the AV board, that has the flyback on it. Of course these sellers can't tell if the flyback on the board actually works. It might well be dead, too. So indeed, the first board I bought (for 20€), had a dead flyback, but the second board I bought (for 10€) had a working flyback. Just pure luck.

 

[doctor_dog]

Thank you for sharing your repair experience, I'm glad you were able to get a hold of a replacement part. My understanding is the transformers are negatively affected by heat (and the poor cooling inside the iMac). I'm considering performing a similar modification to the below, adding some cooling and (hopefully) prolonging the life of the transformer. Putting the link here should you wish to do the same:
https://mac-classic.com/articles/imac-g3-cooling-modifications-part-ii/

May I ask if you performed the board swap yourself or if you had it taken to a repair person? Bonus question: did you source the AV board from eBay?

 

[naujoks]

I carried out the repair myself. I found the boards on a small ads website (in Germany).