iMac G3 (Slot Loading) Doesnt Turn On

Hey Richard,
That cap is probably OK since all the ones in working machines I have ( ~ 10 ) all have that domed cap. The one PAV I have out has exactly that cap on it and my ESR meter reads it at .06 Ohms, which is good. Besides I don't ever remember replacing that cap in all the boards I worked on. I have replaced about 4 flyback transformers but I've actually never had any luck repairing a dead PAV that had a capacitor problem. I read in my research when I was doing a lot of these that the Orange HV ceramics can go bad but I never found one, didn't know how to test them and where to buy new ones even if I could.
That's why I stopped trying to repair them and just switch the faster logic boards into working PAVs. Currently I have probably 6 iMac G3s in the basement with notes on them "won't turn on", "dim display", "green cast" etc. They'll have to go for recycling.
Richard

Hey Richard,
Have you tried resetting PMU? It can also be the PRAM battery is dead/dying.
You can see the button if you look in the RAM access hatch. You can also replace the battery through the same access door (you need small fingers and a few extra tools help):
"Resetting the Logic Board
Resetting the logic board can resolve many system problems (see
the Symptom/Cure tables for examples). Whenever you have a
unit that fails to power up, you should follow this procedure
before replacing any modules.
4 Unplug the computer.
5 Press (reset) the PMU button on the logic board.
6 Plug the power cord back into the computer and press the
power on button on the front of the computer. If the computer
powers on, go on to step 5.
Note:
If the computer won’t power up, reset the PMU again, this time with the power cable plugged into the computer and go on to step 4.
7 Press the power on button on the front of the computer again.
If the computer won’t start, go to the next step. If the
computer does start, you may have a bad battery.
8 Remove the battery from the logic board. Check that the
battery is good.
9 Wait at least 10 minutes before replacing the battery.
10 Make sure the battery is installed in the correct +/-
direction.
11 Power on the computer and test the unit."
The battery should test at least 3.5 volts.
If none of this works the PAV is probably bad.
Richard

Message was edited by: spudnuty

richard,
So seems to be a PSU issue, where do i point my soldering iron?
There is no PSU in the iMac G3. Well there is but it's called the PAV board which is the big board you see looking down on the top. It basically drives the monitor section (lots of HV). Then the down converter which takes power from the PAV and converts it for the logic board. It's the little board that plugs into the logic board that has all the big caps and inductors on it.
My standard fix for this problem is to find a 350 machine that lights up nicely and swap the 600 logic board into it. (heat sink needs to be moved)
I have repaired the PAV but only if the flyback was bad (can't get that part any more). Never had luck repairing the high voltage caps, don't know where to buy them and never figured out which ones go bad even tho' I have an ESR meter.
I did figure out that the down converter takes a +- 26 VAC power feed and thought of going headless w/ a LCD monitor but that's as far as that project got.
Richard

Message was edited by: spudnuty

Hey richard,

Down converter board seems fine,

Yah never seen one of those go bad.

there's a big fat 470 micofarad 400W/V capacitor on the PAV board by the neck of the tube and it clicks when wobbled, could be a dry joint,

I've got a PAV that's pulled and that cap on it also clicks. I think it's because it's hot glued to the board.

on the other hand it's got a bit of a rounded end, not a flat end, ouch1

It's also domed on top as are all the other ones I see of that model.
( There were at least two types of PAVs in this model.)
Richard