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iMac G3 power issues

Posted by: sonic84 on 2022-10-01 23:31:35 Hello, I have an iMac G3 Graphite with power on issues. Specifically, when the power button is pressed, there is an "electronic energize" noise briefly from the CRT and the logic board DS9 LED blinks twice then goes dark. There is no boot chime or CRT screen activity. I stepped through the troubleshooting steps for RAM reseat, SMC reset, PRAM battery voltage check, J9 +5v trickle power check, and DCO voltage check at C4. Trickle power is present with the proper voltages, however the iMac still fails to start up. I checked for obvious signs of component failure (board goo, popped caps, cracked packages, etc...) on the logic board, DC board or CRT board, but didn't see anything. I want to test the components on the startup circuit/SMC, but I do not know where it is on the board specifically... Is anyone here familiar with this iMac model who can point me in the right direction? Thank you! model: M5521, DHHS: GX, EMC: 1857 with Logic Board part# 820-1275-A.

Posted by: cjtmacclassic on 2022-10-02 07:35:05 I don't have a solution but can confirm that a grape iMac in my collection failed in the same way, with visible electrical arcing near the flyback's connection to the tube. It's my understanding that certain iMacs of this era are prone to internal failure of the flyback transformer. I tried to buy a new power board to fix this but, naturally, the flyback transformer was broken in shipping. It's been sitting since. Edit: 3 second clip of the issue: iMac G3 flyback failure Enjoy the videos and music you love, upload original content, and share it all with friends, family, and the world on YouTube. youtube.com

Posted by: sonic84 on 2022-10-22 23:08:52 Hello, I wanted to followup on this. The fix for my iMac was to replace the power board (P/N 6870T194D10). I've got no idea what went awry on the old power board 🙁

Posted by: joshc on 2022-10-23 01:30:07 These are probably approaching the age now where the power boards should be re-capped. Of course, other stuff on there may fail too.

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