All replacement capacitors in iMac G5 PSU burned up

**PCBONEZ** · 02-08-2009, 11:37 PM

Re: All replacement capacitors in iMac G5 PSU burned up

If PSU was at least somewhat working before the repair I would suspect the caps were installed backwards or some solder got away from him (left on the board) and it shorted something out.

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

**nwd** · 02-08-2009, 11:57 PM

Re: All replacement capacitors in iMac G5 PSU burned up

All the replacement caps appear to be inserted correctly. The white stripes on the caps align with the white paint marks at each location.

Before the repair, the computer would only power up after pressing the power button tons of times and then eventually wouldn't power up at all.

After the repair, the computer worked perfectly for a day and was in fact working fine when the burning smell began and I shut the machine down to discover the burn marks at all the leads. The torrid appeared to have cracks in the coating but otherwise seemed fine before the repair. After the burning smell, the coating was pure black and cracking much worse.

I'm guessing that the bad caps caused the initial PSU failure. As the computer was still working when the smell started, would this PSU be likely to be salvageable in the right hands? I'm not sure what to ask the guy who did the work. Thanks again.

**PCBONEZ** · 02-09-2009, 12:55 AM

Re: All replacement capacitors in iMac G5 PSU burned up

The silk screens are sometimes reversed from the 'usual'.
I say usual because there is no official standard so one manufacturer may make the 'white paint' negative and the another will make it positive.
Sometimes they even make a mistake in the silk screen in a few spots.
The trick is to look at the old caps before they are pulled and make a map of the replacements.

Is it possible to fix. - Yes.
Is it practical. - Probably not if you aren't the tech.
The labor could easily run more than just buying a replacement.

I think in your situation I'd look for a working replacement and then have it preemptively recapped. (Since you know the caps tend to go.)

.

**i4004** · 02-09-2009, 12:30 PM

Re: All replacement capacitors in iMac G5 PSU burned up

it's something of a wonder it worked at all...

>I'm not sure what to ask the guy who did the work.

well, if he's fair he should pay for the caps and pay back the labour, if he charged it.

as boinez says, the chances are he put them backwards...ie he didn't look how old caps were installed, but looked just at the white-white match...and that may or may not be correct way...

if you know how to solder change them yourself...or learn to solder and change them...
we can probably help you with deciding what's the ground(minus for the caps) on that pcb.

**nwd** · 02-09-2009, 02:35 PM

Re: All replacement capacitors in iMac G5 PSU burned up

Thank you for the advice, members.

Does anyone know the stats on the torrid that got really hot? It is at position L8 on the iMac G5 1.6 Ghz 17 inch power supply (Apple part no. 614-0293, AcBel part no. API3PC94) sort of right in the middle of everything on the low voltage side. Is this a part that could fail? Is it the sort of thing I can order?

**Wizard** · 02-09-2009, 03:02 PM

Re: All replacement capacitors in iMac G5 PSU burned up

When a coil or a transformer bursts into smoke, it means PSU went SERIOUSLY wrong or missed small capacitors that caused frequency to go way off (too low or high) excessive noise to the point the coils simply heated up like a heater. What guy did bad was missed other capacitors; vital small capacitors that is on the voltage feedback and IC controller that drove the main transistors.

That is where ESR meter is absolute must to check them during rebuilding of a said PSU especially complex type like apple uses.

Cheers, Wizard

**i4004** · 02-09-2009, 03:35 PM

Re: All replacement capacitors in iMac G5 PSU burned up

wizard

>What guy did bad was missed other capacitors; vital small capacitors that is on the voltage feedback and IC controller that drove the main transistors

perhaps you missed this
"the leads of every single new capacitor were brown and melty on the underside of the board"

coil burning was probably just the result of that, not the result of skipping some other (old) caps...ie in such case coil would be burning before swap too...

>sort of right in the middle of everything on the low voltage side. Is this a part that could fail? Is it the sort of thing I can order?

well, first be sure it's destroyed, because it probably is not, even if it's al black...
to go bad wire of it needs to be completely severed(melted to the point of breaking)..
i don't think that happened because it probably would require more current than that psu can produce on ALL rails(and coil was only on one).
this is easy to establish with multimeter: if it conducts electricity it's ok...

problem could be if the isolation is burned to the wire and windings are touching, as in that case it's not a coil anymore...
but we didn't saw your coil so we can't say...

can you find replacement coils? probably yes.... many distributors carry lots of models...you can try contacting acbel and ask for specs(ie inductance of it)

**kc8adu** · 02-09-2009, 05:39 PM

Re: All replacement capacitors in iMac G5 PSU burned up

where that thread worthess without pics smiley?

**Wizard** · 02-09-2009, 06:33 PM

Re: All replacement capacitors in iMac G5 PSU burned up

Every caps? What about small ones like 10uF, 1uF, 22uF 47uF kind?

Cheers, Wizard

**i4004** · 02-09-2009, 09:01 PM

Re: All replacement capacitors in iMac G5 PSU burned up

every single NEW capacitor, ie those that bloke put in....7 pieces.
ie new nichicon caps.
lasting few hrs..better to say burning up within few hrs...

indeed pics would be usefull....we could see the coil and the caps...some nice macro shots of that psu...

**nwd** · 02-09-2009, 09:06 PM

Re: All replacement capacitors in iMac G5 PSU burned up

I showed the board to the tech today. He said that the capacitors were fine, i.e, not burned up - the brownish goo on the underside of the board at each capacitor lead was a material from the soldering process. I don't think the brown stuff was there when I first got it back from repair - did it melt out at high temp? Also, the one capacitor on the low voltage side that was not replaced shows no evidence of brown stuff.

No small caps of the sizes you list, Wizard, were replaced. There are some small ones on the high voltage side but they look fine and I can't find any record of these causing anyone a problem.

I don't think the coil is destroyed.

I apologize if I have misled anyone with my descriptions. I haven't done anything with electronics before. Pics attached - sorry for the wait.

Attached Files

**i4004** · 02-09-2009, 10:14 PM

Re: All replacement capacitors in iMac G5 PSU burned up

yes, i did find it a bit suspicious when you said
"the leads of every single new capacitor were brown and melty on the underside of the board."
but i thought you made a mistake and was actually talking about bad things happening on the component side of the pcb.

goo should bhe from soldering yeah...also if the caps were leaking, i don't think they would pass that pcb and solder to reach to other side...they would prefer to explode thru the top...

**i4004** · 02-09-2009, 10:41 PM

Re: All replacement capacitors in iMac G5 PSU burned up

it seems to me they're not reversed....what were the original caps?
probably not low impedance?

there was one example where replacing gp caps with llow esr ones cause more noise on output....but huh, no burning was involved...

can't think of anything else that would cause new caps to make problems....

unless his soldering work made few unwanted connections...hard to see...is there a physical contact between pins of that cap near the coil?
that 1000uf6.3v cap

**nwd** · 02-09-2009, 11:10 PM

Re: All replacement capacitors in iMac G5 PSU burned up

Original caps are labeled LTec. All are LYZ 105C except for one which is TK 105C.

What may look like contact is where the tech scraped at the brown stuff a bit. I don't see any contact on the underside of the board.

**nwd** · 02-09-2009, 11:55 PM

Re: All replacement capacitors in iMac G5 PSU burned up

Another member describes the exact same symptom with the same coil in the "power supply and design troubleshooting" forum here:

https://www.badcaps.net/forum/showth...highlight=imac

**i4004** · 02-10-2009, 12:50 AM

Re: All replacement capacitors in iMac G5 PSU burned up

diodes on that rail should be checked...send it to wizard..he'll probably fix it...

**PCBONEZ** · 02-10-2009, 04:14 AM

Re: All replacement capacitors in iMac G5 PSU burned up

Looks like tech didn't clean the resin off the board.
Depending on what was used it may be conductive.

**kc8adu** · 02-10-2009, 06:43 AM

Re: All replacement capacitors in iMac G5 PSU burned up

bet the coil got stressed with the bad caps.
its insulation cooked and it got shorted turns.
iirc that one is on +3.3
you might be able to rob one from some junker.its common in many psu's.
look for one with same gauge and number of turns.
your caps are ok.

**i4004** · 02-10-2009, 07:56 AM

Re: All replacement capacitors in iMac G5 PSU burned up

>its insulation cooked and it got shorted turns

i don't think that explains why it's getting hot...what do shorted turns do for a coil with few windings and thats running on 9x % DC?
if anything it should be getting cooler with shorted turns...hehe...

only if some eddy currents develop there....in that metal core, but i doubt current would prefer that path to the wire around it...

All replacement capacitors in iMac G5 PSU burned up

All replacement capacitors in iMac G5 PSU burned up

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