iMac G3 green light of death

[mitchW]

I powered my trusty old iMac G3 Rev A after about 2 years. It powered right on, and it stayed there, until the sleep timer kicked in and machine went to sleep. When I wanted it to wake up, it did wakeup, sorta, but the screen was blank with the green light on. When I turned it off via a power on button, the green light was still on. Very strange. Even when I turned it back on, there was still green light and the screen was blank. There was also no activity from HDD..

It worked, however, when I disconnected and reconnected it to the mains, then there was the standard orange->green light procedure and the picture came right up.

Any info on that? Thanks

Also there was a arc-like snap about 5 minutes after first turned on. Perhaps a high voltage arced somewhere?

 

[Macdrone]

Power supply caps and maybe flyback but you'll want to do the capacitors on the power supply first.

 

[mitchW]

Did a logic board reset and it worked for a while, but after about 10 minutes it still started to act up.

No arcing snaps were heard anymore in about 2 hours of operation, so I believe that there must have been somekind of whisker or dust accumulation and it arced beacuse of that.

So capacitors? Should I change them all or just do an ESR check and replace if there are any bad?

 

[CC_333]

I wonder if it's a logic board issue?

Still probably a good idea to recap everything else, though. Don't bother with doing ESR checks, just replace them. The test will be whether or not the problem still exists after the recap.

c

 

[mitchW]

I pulled out the Power Supply board and the Analog board and did a quick ESR check. Three caps were a bit high, but still within the tolerance window, but I replaced them anyway. Currently I don't really have much replacement caps, and all of them were quality Nichicon-chemicon brand, which usually don't need replacement.

The problem persists, but I found out that when the machine is cool, the sleep and restart work fine, but after about 15 minutes when the machine warms up, it will start to act up this way. With the bad caps, the problems are usually reversed. I would say that there is somewhere a bad transistor..

 

[DragonKid]

It may very well be a bad flyback, tray-loading G3 iMacs were rather notorious for eating them. A bad transistor or cold solder joint is certainly possible, but the fact that you heard arcing at least once may mean that shorts are starting to form in the flyback.

If nothing else, they can still be found cheaply (dalbani.com has most common iMac FBTs in stock) so picking up a spare may not be a bad plan.