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**PCBONEZ** · 02-10-2009, 08:00 AM

Re: All replacement capacitors in iMac G5 PSU burned up

I wonder how many little Chinese girls it takes wrapping wire around doughnuts to keep the world supplied with those things.

You need same size doughnut (core), same wire gauge, and same # turns.
If you find a scrap one that's right except too many turns you can un-turn a few until it's right.

.

**i4004** · 02-10-2009, 08:48 AM

Re: All replacement capacitors in iMac G5 PSU burned up

nwd, what was the cause for you to get new caps?
smell?
same smell as you got now?

if coil was burning before and now, change it.
if otoh coil started to smoke only now, it's not the coil.

**relkin67** · 02-10-2009, 02:44 PM

iMac G5 PS

I performed this same repair about 3 months ago on an iMac G5 I picked up cheap on Craigslist. The original PS caps are ALL Ltec low ESR (the manufacturer's spec sheet, if believed, shows specs superior to Nichicon PW). Now this is a REALLY hot and stressful application - one that seems to separate the boys from the men. Taiwanese/Chinese capacitors seem to really fail in an poorly ventilated PS (which this most certainly is!)

My research indicated that the secondary caps are the first to go followed by the coil here mentioned. I seem to have been lucky because the coil didn't burn yet in mine. I replaced everything electrolytic - secondary AND primary with Nichicon PW, Panny FM (Digi-Key was out of stock on some PW sizes) and a couple oddball sized Rubys I got from Topcat.

Been running 3 months 24/7 without a problem. The iMac was stuffed with dust when I got it so this could have been a contributory factor (you have to open these up every 6 months and dust 'em).

**Toasty** · 02-10-2009, 05:26 PM

Re: All replacement capacitors in iMac G5 PSU burned up

Nit picker here. I expect nothing less in return...

The 'doughnut' with the wire looped around it is called a torrid.

Actually it's a:

toroid - a doughnut-like solid whose surface is a torus .

not

torrid - parched with heat; hot <torrid sands>; giving off intense heat; scorching

Actually, since it's cooked, it's a....

TORRID TOROID !!!

LMAO

Sorry,
Toast

You may now return to your regularly scheduled drinking.

**Wizard** · 02-10-2009, 05:32 PM

Re: All replacement capacitors in iMac G5 PSU burned up

LOL Indeed!

Cheers, Wizard

**i4004** · 02-10-2009, 06:36 PM

Re: All replacement capacitors in iMac G5 PSU burned up

i find nothing weird there...i noticed it too, but i know bonez is horny, so it's an easy typo to make...hehe...

**Toasty** · 02-11-2009, 01:56 AM

Re: All replacement capacitors in iMac G5 PSU burned up

I would check to see if the core is indeed shorted to the windings.

Since it looks to be bare metal where the insulation has flaked off on top, first check the core itself with an ohmmeter to see if is conductive. Set the ohmmeter range to read in the x5k or less range and put both leads tips on that bare spot on top. If it gives a reading, it's a powdered iron core. If you get no reading the core material is ferrite.

If it's powdered iron: Place one ohmmeter probe on the core, check to the underside of the board where the cores leads come through. If you get a reading from the core to either lead, it's shorted and will need to be rewound or replaced. Also, I'd wiggle the core about to see if it has an intermittent short.

If it's ferrite: Since the core has overheated (obviously), its mµ (magnetic permeability) is destroyed, and may be causing the problem. Rewinding the toroid is not an option. Replacement only.

On the other hand, if it is an iron core and the coil is not shorted, then the core is okay and the cause of the overheating likely lies elsewhere.

Replace the cap that you didn't unless you can prove it's not faulty with an ESR meter. It could be that now that everything else is running correctly, it can't handle the stress of the frequency and/or ripple current. That may be causing the coil to go hot.

Can you run the supply free of any load? Does the toroid get hot then?

Has an overload condition on the motherboard been eliminated as the cause of the overheating? ie. more bad caps? MOSFET's?

Toast

**PCBONEZ** · 02-11-2009, 02:10 AM

Re: All replacement capacitors in iMac G5 PSU burned up

Originally posted by Toasty

Nit picker here. I expect nothing less in return...

Actually it's not: Nit picker,,, it's: Nitpicker

**i4004** · 02-11-2009, 12:53 PM

Re: All replacement capacitors in iMac G5 PSU burned up

^^
lol!

**nwd** · 02-11-2009, 03:49 PM

Re: All replacement capacitors in iMac G5 PSU burned up

What specs do I need to know to get a proper replacement coil inductor? Is the gauge and number of coils sufficient or do I need more info - H value? Does the core have specs I need to know? What does the +3.3 refer to in kc8adu's post? Voltage?

Thanks again.

-Nate

**nwd** · 02-11-2009, 05:24 PM

Re: All replacement capacitors in iMac G5 PSU burned up

Sorry for the inductor spec question - didn't see there was a page 2 of replies.

In reponse to i4004, replaced caps only because computer would not power up. 7 secondary caps looked swollen and a couple had a little brown stuff at the top. No smell prior to repair. The coating on the coil was cracked and split before repair but not black at all.

I definitely had to get in and around the coil with an exacto knife to clear all the putty that was in there so the caps could be freed. Could it be possible I damaged or altered the coil during that process?

In response to Toasty, motherboard caps look fine - not sure about MOFSET. I believe a different model iMac had much worse motherboard cap issues.

After moving the windings on the coil around a bit, I plugged in the power supply without load. It's been running without heating up for about half an hour now. The computer had been working fine for a day or so before the smell started originally.

I am so thankful for all the comments and advice from so many members.

I'll pop it back in the machine under load and see what happens. I'll also look into finding a new coil.

**nwd** · 02-11-2009, 05:37 PM

Re: All replacement capacitors in iMac G5 PSU burned up

Yep, under load, that coil heated up right away. The computer worked fine but I shut her down.

**nwd** · 02-11-2009, 06:28 PM

Re: All replacement capacitors in iMac G5 PSU burned up

The one unreplaced cap is a real bear to free, which, since it looked okay was not replaced. I believe the tech tested it in place but I need to verify that.

-Nate

**PCBONEZ** · 02-11-2009, 09:29 PM

Re: All replacement capacitors in iMac G5 PSU burned up

I think the Toriod is shorted like KC said.

If a shorted Toriod worked they wouldn't use them, they'd use a piece of wire instead.

**i4004** · 02-11-2009, 10:53 PM

Re: All replacement capacitors in iMac G5 PSU burned up

>No smell prior to repair. The coating on the coil was cracked and split before repair but not black at all.

to me this suggests it's not a coil's fault, but given you don't have real choice try to replace it.

this
https://www.badcaps.net/forum/showpo...58&postcount=3
does and doesn't make sense.
it doesn't make sense because after the repair coil shouldn't be getting hot at all, so what's there to deteriorate it further?
ie if he had come cracks, ok fine, it was because of badcaps, but what is it now to make it COMPLETELY BLACK in one day?
i don't think one can call coil with few turns shorted at all, what's there to short? resistance goes from 0.050ohm to 0.049?
bleh...and like i said i don't think core material condusts more than wire, so why should current go there at all?

here
http://www.jimwarholic.com/docs/Appl...wer-Supply.pdf
i don't see coil mentioned at all...

>I definitely had to get in and around the coil with an exacto knife to clear all the putty that was in there so the caps could be freed. Could it be possible I damaged or altered the coil during that process?

good question...but why did starter of that other thread ask this
"Is there another cause for the coil frying itself?"

anyhow, change it and we'll know....heh...

>Is the gauge and number of coils sufficient or do I need more info - H value?

how will you find out the h value?
if you can, sure, if you can't wire gauge, dimensions, and number of coils will suffice...

bonez, you're now talking of "toriod".
just say "coil".

**PCBONEZ** · 02-11-2009, 11:05 PM

Re: All replacement capacitors in iMac G5 PSU burned up

Yes i4004, we know you don't understand.
... But believe it or not they use coils because they are needed.
... And if it's shorted -> it don't work.

.

**i4004** · 02-12-2009, 12:18 AM

Re: All replacement capacitors in iMac G5 PSU burned up

>And if it's shorted -> it don't work.

indeed, but if it "don't work" why is it getting hot...
hehe..

and to say "shorted" for few turns coil still sounds lame...
its (miniscule anyway) inductance may be shot(if turns touch etc.), but like i said, that would make it heat LESS than if more turns are used and it had higher inductance...
because it's effectively becoming a jumper, and why would jumper heat up?

two possibilities:
-eddy currents produced in the core because naked wire touches the core...

-not coil problem at all, but changing caps changed the circuit characterictics, so coil is for some reason(particular frequency/amplitude of ripple) loaded more that normal...
also, much higher current will flow if mobo is drawing too much current...those badcaps were there for some time, did they hurt the mobo?

to that extent toasty said it all
https://www.badcaps.net/forum/showpo...6&postcount=27

------------
yeah, i am curios why is it getting hot...you obviously are not....you're just..torrid..again...hehe...

**PCBONEZ** · 02-12-2009, 01:01 AM

Re: All replacement capacitors in iMac G5 PSU burned up

What does an inductor do i4004 ?

**kc8adu** · 02-12-2009, 02:32 AM

Re: All replacement capacitors in iMac G5 PSU burned up

think of your coil with shorted turns like a transformer with its secondary shorted.

**PCBONEZ** · 02-12-2009, 03:22 AM

Re: All replacement capacitors in iMac G5 PSU burned up

Here's a hint i4004.
- An inductor to a circuit is as a flywheel to a machine.
[Come on... I KNOW you know.]

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