iMac G5 power supply w/burning coil

[eratosthenes]

This is my first time trying to replace the caps on this power supply. I have seen many of these PSes fail from bad caps, but they also appear to take out a coil at position L8 on the PS as well.

After replacing the caps, my PS worked for about a week, then started smoking again. I found this coil had turned into a heater, burning off all of it's insulation.

Has anyone else seen this? Does the coil have to be replaced? Is there another cause for the coil frying itself?

[nwd]

Re: iMac G5 power supply w/burning coil

I just posted about this exact thing in another category. I had all the bad caps replaced in the iMac G5 17 inch power supply. Worked fine for 1 day and then burned up - same torrid at L8 fried just like yours.

What the heck?

-Nate

[Krankshaft]

Re: iMac G5 power supply w/burning coil

The coils insulation was probably partially melted by the bad caps the first time that deteriorated the insulation enough to heat the coil below the point of catostrophic insulation failure. It looks like the heat was finally too much.

As for repair it depends on how bad the damage is if the core is still okay you could manually rewind the core with new insulated wire.

Is this a torroid or as I call the other type a coil spring like coil (one that has insulating wire wound up a straight core?

The torrid would be more labor instensive then the coil spring type.

You would have to measure the thickness of the original wire with a digital micrometer and count the turns of wire on the core as you are removing them.

If you know how many uH the old coil was you could just buy an off the shelf replacement. The coil is probably for filtering noise on one of the secondary rails.

[PCBONEZ]

Re: iMac G5 power supply w/burning coil

There are 3 or 4 Toroids in that PSU.