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(2) iMac G4 Luxo and PSU Caps

IIciNov90

Well-known member
Howdy,

I have (2) different 17" iMac G4 systems. One is a 1.25 GHz system that I bought new. The other is a very nice but slightly less capable 1 GHz system from the prior model year that a friend gave to me when she said her system started to not startup when pressing the power button and then the Apple Store told her that the power supply was bad and it was too much $ to be worth fixing.

I used my iMac G4 for 8+ straight years and in the time I had it maxed out the RAM to 2GB and also upped the internal HD to a 320GB Seagate Barracuda. I finally replaced my iMacG4 with a Mini Server 2011 Core i7. At that point I had already had the slower iMac from my friend for about a year. I originally tried to start it once and it was as she said - DOA non booting. I decided to shelve it for another day as I was restoring my beloved Iici with some nice tantalum caps.

Interestingly, my own G4 within a month after getting the Mini decided to act up in the same exact way as my friends older 1GHz system (The timing made me swear it was like it was almost jealous or sulking over the Mini). At this point, both iMacs were shelved. Starting about 3 weeks ago, I unshelved them. I decided to buy new 3.6V motherboard batteries, some thermal paste and a 1GB DIMM for the internal MB slot on the slower iMac. When the parts came, I opened up both of the cases side by side. While they both had dust, my friend's former system was PACKED from bottom to top with dust. While my own system was easy to open up due to my prior upgrades most likely, the motherboard on my friend's old system was completely bonded to the heatsinks. No amount of gentle pulling or twisting would release the board from the sinks and I worked it for probably a good solid 25-30 min0. It was almost like someone had used the permanent epoxy type of arctic silver. I really pulled but I could tell that if I were to pull harder it could break the motherboard or bend the heat pipes. I was really stuck until I did some web searching found something obscure a British guy who had been stuck as well had posted. In his case he reinserted the retaining screws loosely engaging maybe a thread or two. Since the board's layer did not have threads, he then was able to carefully "tap" off the board while immobilizing the motherboard's layer. It was the first time I have ever used a hammer (albeit a small one) to gain entry to a computer case. It kind of gives the term "Case Cracker" a new meaning. I succeeded with no damage!

BTW, the total amount of dust I removed from my friends old iMac was enough to pack into the shape of a good sized hamster. It was an amazing amount. I got it all out by hand and with compressed air.

Cleaning off the old thermal paste residuals took a while and then I changed the battery and added the 1GB DIMM as well as added the new battery to my own 1.25GHz system.

I pressed the PMU (JUST ONCE!) quickly for each one, applied the new Arctic Silver paste and then closed them up. I reattached the power cords and keyboards & mice and when I went to try them out, neither one would boot. (Grrr!)

After pressing the 1.25GHz power button several more times it eventually booted up and auto synched the time and date off my wireless like it had never been missing. I shut it down, it started right up again. I left it overnight and the next day it would not start. Nothing I tried would start the older system from my friend.

I decided to think about things some...

I found this interesting youtube video:


Could it really be that easy?

I tried it out on my friends former system since it was the worse of the 2 and it actually started!

All of the RAM I installed was showing up fine. As a bonus, it still had its Appleworks - something I lost when I downgraded my iMac back to Tiger from Leopard. My 1.25GHz system started without the blowdryer.

I shut both of them and restarted the older iMac into Firewire direct mode where I recovered my long lost Appleworks and copied it back onto the 1.25GHz system where it worked fine. I then cloned my own 10.4.11 system back onto the older iMac and then shut both systems down. The next day BOTH iMacs started on one push of the power button with no blow dryer!

I did not expect that...

I think that the PSUs on both of these iMacs are marginal with my friends former system being the further along of the 2. A warmer ambient room temp seems to maybe help some. (The temp is abut top drop back down very cold in the next day so I will confirm this theory)

I am guessing it is the PSU CAPS that are on their way out. There is not much out there about replacing iMacG4 caps the way there is for older systems like my Iici or SE/30s.

I really like these machines and plan to have them as audio servers with all of my CDs ripped to lossless files. I also like that they have full height CD/DVD drives on par with the Pro Towers. I think they are as iconic as the original compact Macs.

I truly admire these systems and was quite resentful towards the inferior crappy overheating replacement slot-loading G5s when they "ruined" the iMac. While the current one piece iMacs are much much better I have always held out hope that a Luxo style iMac will someday return. A Mac Mini Core i7 guts in the Luxo form factor would be killer.

Does anyone have any experience with recapping the power supplies on these iMacs? Checking online, the power supplies for the 1.0 and 1.25GHz 17" iMacs are the same though different vendors have made them both.

If I hear nothing from here, my plan is to reopen these cases, remove the PSUs and then to replace all of the PSU CAPS with new identical value but higher temp/higher quality pieces as they are probably too big for Tantalums.

Any thoughts?

Brian

 

TheMacGuy

Well-known member
My Luxo did this once. It just flat out refused to boot. I could hear the fan come on though. I freaked (of course). I went through all the started troubleshooting steps, and a SMC followed by a PRAM reset fixed everything and have not have any hiccups since then. It could be anything. Just keep an eye on it. Interesting, mine is a 2003 1GHz model, like the one your friend gave you.

 

IIciNov90

Well-known member
> It just flat out refused to boot. I could hear the fan come on though.

With these 2 iMacs of mine it is nothing (no fan.) the power cord might as well not even be connected.

The cold is back with a vengeance to the U.S. East Coast. I am going to see if they boot under much colder ambient air tomorrow morning. They (and all of my old Macs) are in a partially finished upstairs that is quite drafty. The temp will be around 60F at boot up time. If they happen to boot in the cold then Merry Christmas to me. Otherwise it is definitely CAPS replacement time. I will probably go for those ESR CAPS since they seem ideally suited for power supply applications.

> Interesting, mine is a 2003 1GHz model, like the one your friend gave you.

Are you still on your original 3.6V MB battery? If so, it might be time to open it up for a replacement. With the battery replace, it's also the ideal time to up the internal 256MB DIMM to a 1GB and max your Luxo baby out if you have not done so already. If you have never opened it before, have some compressed air standing by. You probably have enough dust accumulation for building your own dust hamster as I did. Also, watch for the very tightly sticking motherboard. If mine was like that then chances are that yours is too. The original Apple (foxcon?) paste apparently becomes evermore gluelike with age.

I will post back with my Christmas Day cold boot results tomorrow...

Brian

 

TheMacGuy

Well-known member
Otherwise it is definitely CAPS replacement time. I will probably go for those ESR CAPS since they seem ideally suited for power supply applications.
It could be a cold solder joint because once heat is applied everything starts working.

Are you still on your original 3.6V MB battery? If so, it might be time to open it up for a replacement. With the battery replace, it's also the ideal time to up the internal 256MB DIMM to a 1GB and max your Luxo baby out if you have not done so already. If you have never opened it before, have some compressed air standing by. You probably have enough dust accumulation for building your own dust hamster as I did. Also, watch for the very tightly sticking motherboard. If mine was like that then chances are that yours is too. The original Apple (foxcon?) paste apparently becomes evermore gluelike with age.
Nope, I replaced the battery along with the HDD earlier this year (upgraded to a SATA SDD with and adapter). Upgraded the internal DIMM with a 1GB I pulled from an older HP tower, although the external SODIMM is a 512MB upgraded by the original owner. When I opened it up, I had very little dust and and no problems with the thermal paste. Of course I removed and reinstalled the thermal paste for optimum cooling while I was in there.

 

IIciNov90

Well-known member
When I opened it up, I had very little dust and and no problems with the thermal paste.
Nice! It sounds like you took extra good care of your iMac as I have done with my 1.25GHz one. That's definitely a lucky break that yours cooperated and released its motherboard from the sinks without the issues like the one from my friend. I was thinking that there was so much dust in that one that maybe it restricted airflow and ended up overheating and baking/curing the thermal paste to a hardened state with much higher tensile properties in adhesion and cohesion. I'm really glad I took my time and did not get impatient and try to force it.

I'm not sure about the cold solder theory, if I have to open them up again I will certainly look closely at all of the joints. I wonder though, why now and why both of them? I have heard of cold solder joints as faults in new systems but not developing over extended time periods. They are both 10-11 years old and the startup issues only started during the last few years with the older one seemingly a bit worse in a manner commensurate with its greater age. Since the power supplies are identical for the 1.0 and 1.25 GHz systems it sounds like a failure mode that is likely common between the 2 systems.

I will certainly learn more tomorrow morning when they get the cold room cold boot test and will post back with the results.

Brian

 

techknight

Well-known member
It could be a cold solder joint because once heat is applied everything starts working..
Thats caps. The hotter they get, the internal ESR drops, and capacitance goes up. Thats how you snuff out bad caps is heat.

 

IIciNov90

Well-known member
The results are in:

I went upstairs this fine frigid Christmas Day and I pressed the power buttons JUST ONCE on each iMac and what do you know, they fired right up.

The room is COLD and probably closer to 55F.

It appears that they made a liar out of me.

I guess those old PSU CAPs still have some life left in them after all.

I only shut the systems down yesterday afternoon. Could the PSU CAPs still have been holding enough residual charge?

Maybe I will power down and wait some longer period before trying again. I'm thinking maybe a week.

Any thoughts out there on what's long enough to fully discharge the CAPs?

Brian

 

IIciNov90

Well-known member
It got really cold in the upstairs and I went to start the 2 iMacs albeit a bit earlier than I said I would. The older one will not start now, even with the blow dryer trick. The newer one took a few tries after the blow dryer treatment. There were a couple of false starts where the fan would start to spin but not quite and then finally a boot up.

My plan is to take out the power supply on the older iMac and to inspect and replace most if not all of the caps with higher temp low ESR CAPS. CAPS are cheap enough so I will double up on my buy and after the first one id fixed I will go and to the other iMac. There are variations even amongst the same models for these PSUs but I will chance it.

It may be a few weeks but I will report back on how well this turns out.

Brian

 

CC_333

Well-known member
Hmm, this sounds like my eMac. It won't boot unless I put it in a 120ºF storage shed on a hot summer's day (problem is, I would end up crashing if I stay too long, so I can't use it much when it's working :lol: )

I suspect it's bad capacitors, both in my case and in yours.

Good luck!

I wonder if this means I should recap my iLamp's PSU?

c

 
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