iMac G5 won't boot after capacitor replacement

[patdrums]

Hi all-

I have an older pre-iSight 17" iMac G5 that fell victim to the bad capacitor issue so common for them. After my original problems I took it to a Mac repair shop and was told I had bad caps on both the logic board and power supply. I replaced it with a new iMac a couple of months ago and decided before trashing the old one, I'd give the DIY cap replacement a shot. I got all the caps and dove in headfirst. (I do have a little soldering experience and wasn't afraid of taking it on)

I replaced all the bad caps in both the power supply and on the logic board-about 25-30 of them total. Everything went well and there were no snags. When I reassembled it and booted it up I got nothing but fan noise and the front power light. I called the Apple repair shop and told the tech what was happening and he said it sounds like it's failing POST. I just opened it again and rechecked all my solder joints and made sure they were good. I did find a couple of questionable ones so I thought maybe that would fix it. No luck. Anyone run into this before and have any suggestions?

As I said I've already replaced it with a new one so the whole point was to see if I could get this one back up and running, wipe it clean and set it up for my daughter to start learning how to use a computer. If I can get it working, great. If not, I'll toss it or sell it for parts. No biggie either way. At this point it's just principle. It's THAT close and I hate to give up! I know I can do this! : )
Anyone know of something I may be missing?

Thanks in advance....

 

[John T]

I had the same problem on my old G5 and carried out the PSU repair.

How did you know how to identify the "bad" caps? It's unusual for caps to be a problem on the logic board, it's usually the PSU on this model of the iMac. Have you checked the output voltages of the PSU? Were all the caps you replaced the electrolytic type? Have you checked for their correct polarity?

 

[djc6]

have you tried asking on this forum?

http://www.badcaps.net/forum/

Pretty sure it's the premier forum for DIY capacitor replacement Isn't the internet wonderful?

 

[patdrums]

I had the same problem on my old G5 and carried out the PSU repair.

How did you know how to identify the "bad" caps? It's unusual for caps to be a problem on the logic board, it's usually the PSU on this model of the iMac. Have you checked the output voltages of the PSU? Were all the caps you replaced the electrolytic type? Have you checked for their correct polarity?

I bought a package set of caps from jimwarholic.com that came with all the caps necessary to make the swap. Several of them were bulging badly and leaking--those were obvious to the naked eye. The others looked okay at first glance but I swapped them anyway as per the diagram and instructions that came with the replacements. Several caps on the motherboard as well as the PSU were obviously bad. I made sure to check the polarity and voltage ratings of all of them carefully before installing them so I know they're in correctly. I have not checked the output voltages, mainly because I'm not enough of an expert in electronics to know how to do it correctly. I'm savvy enough to open the case, disassemble it, solder in the replacements and get it all back together but I was hoping that it wouldn't take much more than that. Apparently, the project may be a bit over my head. Most people I've read about who have had success doing it haven't been electronics experts and I figured I could tackle it as well. At this point, it's just a matter of refusing to be defeated for me! I'm almost there so I'm just asking around for any tips, pointers or info that I may be able to apply to get it working. If it simply won't cooperate, I'll use the thing as a doorstop! Thanks for your reply. I'm gonna keep looking in the meantime.

 

[rtrt]

probly worth posting on Jim Warholics comments board as well as the bad caps link above.

if it were me i'd start with the psu - there is a diagram of the pinout & voltages on Jims site iirc or find one elsewhere.

you need a multimeter to measure the voltages - not too expensive to buy - or maybe borrow one.

there is one problem with that tho - think the psu doesn't switch on unless its connected to the motherboard.

think there's a way to 'trick' it - Jims board maybe a good start?

 

[djc6]

perhaps this new issue isn't capacitor related? maybe something broke or wasn't reconnected properly in the disassembly/reassembly process? CPU/RAM/etc need to be reseated?

 

[John T]

From what you say, it's a good bet that the trouble lies somewhere in the soldering. The actual tracks on PCB's can easily be damaged (particularly on the multi-layered types found in computers) and together with the surface mounted components, don't like being overheated - which is easy to to do when de-soldering! It is also easy, if not experienced, to make dry joints, where the solder has just "glued" the connection and not correctly run around the joint, making a good electrical connection. These can be identified by examining each joint under a magnifying glass. The solder should have a bright and shiny appearance and not dull and grey.

Without the necessary meter to check that the PSU is actually working OK, the only thing I can suggest you do is to go over all your original solder joints with a hot iron. Just touch them long enough for the solder to run again. Then, remove the iron and blow on the joint to cool it quickly. This should get rid of any dry joints.

If all fails and you are still in a fixing mood (!) there's always eBay. You can often find non-working G5's being sold for next to nothing just for spares. With luck you could pick up a replacement logic and PSU board.

 

[broandrew]

iMacG5 capacitor replacement

I also bought a package set of caps from jimwarholic.com that came with all the caps necessary to make the swap. I replaced
all the larger caps for the POWER INPUT, tht came with the $17 kit. The Apple store guy said I would eventually have to buy a new computer. Our IMac G5 ( first issue model) had a streaking screen when starting up, it would clear once warmed up, this went on for 6 months, then one day : deadness, just a black screen. Don't have $1500 laying around for an intel Mac, but did have $17, I decided to gamble, I can solder. So I spent 3 hours taking out caps and soldering ( the use of a solder sucker was needed.) and replaced the caps, made double sure I had the right ones in the right spot. I only replaced the power inputs in the power supply box. Well it did not fire back up. I was bummed, oh well. Two days later I find my 7 yr. old daughter on the iMac playing her doll dress up game online!! I said baby what did you do to fix the Mac. She said she just turned it on. She did meantion in went black screen only noe more time, but he restarted and it has been working GREAT! ever since!! Yipeee it worked!! I still enjoy the PowerMac G5. The intel mac will have to wait till a later year. I recommend the fix, not rocket science you can do it. I believe th caps took time to charge up before working correctly. They do hold a charge like a battery, that is their purpose to take and release electrons slowly ramped up and down. Go for it!!