On 6/17/10 6:06 PM, Jim Scott wrote:
On Jun 17, 2010, at 5:30 PM, Clark Martin wrote:
I acquired an iMac G5 20", no camera (A1076), it doesn't power up.
On plugging in the power cord one diagnostic LED comes on.
Resetting the SMC doesn't help. PRAM battery is good. According
to Apple test procedure it's a bad logic board. One set of caps
was blown out, I replaced them (after much trials and
tribulations). All the others looked okay.
Does anyone know a likely culprit, fix, test? According to the
original owner it was taking more and more attempts (button
presses) to start up before it wouldn't start at all.
The problem very likely is bad capacitors in the power supply, as
well as on the logic board. I've gotten the first diagnostic LED to
come on in that generation of G5 iMac, which simply means enough
power has gotten to the logic board to turn on the light. But after
replacing the power supply capacitors (which I got
here<http://jimwarholic.com/2008/07/how-to-repair-apple-imac-g5.php>),
I got three lights and the iMac booted, even though there were more
than a dozen leaking/bulging caps on the logic board.
I've also done the same thing and gotten only two lights and some
whirring from the hard drive. All the caps on the logic board looked
OK, which is no guarantee they're working correctly by the way. After
replacing the caps, I got three LEDs and the iMac booted.
The caps in the power supply are much easier to replace than those on
the logic boards, as you probably know. Make very sure that the
replacement caps are soldered solidly to the boards. I examine the
soldered legs of my replacements with a magnifying glass while gently
wiggling the cap. It's very difficult to get new caps correctly
soldered since Apple used lead-free solder with a high melting point
during manufacture. As you already know, it's a
trial/error/tribulation process.
So you've got a lot of fun waiting to eat up hours and hours of your
life. And all because someone stole an incomplete recipe for
capacitor electrolyte from a Japanese company in the early 2000's.
What's really evil, though, is that you can't tell a bad cap from a
good one. I've had iMacs with obviously bad (bulging tops, leaking
electrolyte, tilted because the bottom seal had blown) capacitors on
the logic board run just fine. And I've had iMacs with
pristine-looking logic board caps fail to boot even with a known-good
power supply.
Thanks, that gives me hope. I did look inside the power supply and one
cap was bulging so it goes on the list of parts to replace.
--
Clark Martin
Redwood City, CA, USA
Macintosh / Internet Consulting
"I'm a designated driver on the Information Super Highway"
--
You received this message because you are a member of the iMac Group, a group
for those using Apple iMacs and eMacs.
The list FAQ is at http://lowendmac.com/imac/list.shtml and our netiquette
guide is at http://www.lowendmac.com/lists/netiquette.shtml
To post to this group, send email to imaclist@googlegroups.com
To leave this group, send email to imaclist+unsubscr...@googlegroups.com
For more options, visit this group at http://groups.google.com/group/imaclist
