iMac G3 Unusual power supply problems

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I've just been given a G3 iMac, bondi blue sloat loader 350mhz.

When the power button is depressed, I hear the crackle of the monitor firing up... but nothing else happens. No LEDs light, the drives don't spin. Then several seconds later the CRT is heard discharging again. This happens again if I hit the power button again.

It doesn't seem like the common as mud flyback failure because the LEDs don't light at all.

The large 470uF capacitor next to the flyback has a rather large bulge on the top but I'm told this is normally, and cursory peering through the lid of another iMac it looks like it may be at least a little bit bulged and still work. I can't see anything obviously burned out on the analog board but I haven't been able to remove it and check that capacitor yet.

Anyone seen this before or know what might cause it? The logic board and drives are known to be good for one thing.

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Michael

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Ex-parrot's picture
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It doesn't seem to get as far

It doesn't seem to get as far as powering up the degaussing coil either.

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Michael

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5v trickle power is present o

5v trickle power is present on the board, so is the -1.2v DC0 voltage.

The downconverter board voltages aren't present when I hit the button and merely fluctuate a bit, but stay under a volt.

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Michael

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Replace PSU?

When I had the same problem I replaced the powersupply.
I'm gonna do it to the 500 mhz too (though I need to find a solution to the green screen problem).
My conversion here:
http://www.applefritter.com/node/10574
I'll be making a new case for it this month.
David

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iMac G3 400mhz, custom power supply, no case - yet

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Re: Replace PSU?

dMac4 wrote:

When I had the same problem I replaced the powersupply.
I'm gonna do it to the 500 mhz too (though I need to find a solution to the green screen problem).
My conversion here:
http://www.applefritter.com/node/10574
I'll be making a new case for it this month.
David

Thanks for pointing that out - that is one option for me I suppose. Your documents on the power supply and video connectors are useful.

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Michael