So i've recapped a iMac G5, 1/2 succes

[didius]

About a year ago I got an iMac G5 20" ALS, which wouldn't boot, for a steal Since it could be a caps issues I went for it. Sadly enough it wasn't. It seemed a logic board problem.

Recently someone offered me an other broken iMac G5 which had fallen from his desk and the casing was cracked. I went for it thinking I might build 1 iMac from these two.

Opening the second iMac up, I noticed leaking caps. I ordered new caps online, but pfew, replacing them isn't a walk in the park! Here how I tried to replace them. I have a 40W soldering iron which can reach up to 450°C and a hot air soldering station which can reach up to 500°C.

These are the caps I replaced:

Near the video: C5003, C5002, C5009: 3x 1800muF at 6.3V
Near the memory: C902, C903, C910: 3x 1800muF at 6.3V
               : C1653: 1x 120muF at 16V
               : C909, C908: 2x 1500muF at 4V (did not replace)
Near the WiFi: C1703, C1603: 2x 120muF at 16V
Center left: C3311, C3417, C3422, C3412, C3321: 5x 1000muF at 16V
           : C1009, C1010: 2x 1800muF at 6.3V
Center bunch: C3318, C3328, C3418, C3321, C3427, C3333, C3474, C3317, C3472, 
              C2203, C2209, C2208, C2202, C3473, C3417, C3475: 16x 1800muF at 6.3V

First step: desoldering the old caps
A) First: the iMac G5 motherboard uses lead-free solder which melts at much higher temperature. I used my hot air soldering station at 430°C to get it to melt while pulling the old caps out.

By pulling the caps out it sucked some solder into the solder holes, this proved difficult to remove.

B) Second: I used some solder wick to remove the remaining solder using the soldering iron. This didn't clean the solder pads completly, but removed some solder.

I couldn't fit the new caps in yet, because some solder got into the solder holes. I had to get this out before I could fit all the new caps in.

C) Third: cleaning out the holes.
I tried using the legs of led lights to to clear the solder. Pushing them (and taking the solder with) through while heating it with my hot air station, this was not a good method.

As you can see I burned the mother board near the wifi.


Also I fear I pulled some solder pads while desoldering this way.

I then tried a better method, heating one side up and using a solder sucker on the other side. This worked very well! I got most of the old solder out.

Second step: soldering in the new caps
Because many solder pads still had some old solder on them, or the solder pads were destroyed (not sure ) not an easy task. Much solder joints are poorly done. I tested the soldering using a probe and the old board. It seemed fine.

Ugly solder joints


The new caps in place:


Because after cutting the solder joints I feared they would touch the G5 heat sink and short out, I covered them with capton tape.

Testing it out
I applied fresh cooling paste on the G5 processor, and put everything back together: First boot:


Oh no! PRAM and SMU reset:

Looking much better!

It didn't seem to boot however, safe boot was working though. I tried removing the bluetooth and the Airport card since I burned the motherboard near those. But that didn't help.
I just finished updating the system in safe mode and, now I can boot without issues !

I'm anxious to test it out for a longer period and see the soldering job really worked.

 

[Altemose]

A quick note for those looking to attempt this repair: Apple used lead free solder on these G5s that require a much hotter soldering/desoldering iron to melt compared to regular solder.

 

[AC910]

Nice work.

If you're planning on more soldering work I highly recommend a desoldering gun. They remove solder from pins and PCB holes almost instantly which minimizes heat applied.

 

[Altemose]

Just don't get a cheap Chinese desoldering gun, as they don't tend to handle desoldering caps on those logic boards very well. I owned both a RadioShack model and a cheap eBay special: the RadioShack model could barely melt the solder and the Chinese special burned a hole right in the board.

 

[Simone.m]

Why hot air instead of the soldering iron? I did a similar work using a Weller soldering station with a 0.8 iron and a pump for cleaning the solder, it worked flawless

 

[didius]

@Simone.m I own a 40W soldering station (Aoyue 936), but that didn't seem to do the job with a 0.8mm tip. I could get the solder to melt using a big tip (+- 3mm) but it wasn't practical.

Using the hot air was pretty easy and I'm sure if I would do it again, I would be doing a much better job
[doublepost=1470825428][/doublepost]One might be wondering why I put in "1/2 succes", here's why:

I've been using the iMac a week now, and it's not in tip top shape.

It's working fine most of the time, but rarely, at strange occasions the squares like in the 4th picture appear. I tried to pinpoint when it happens. At first it seemed to happen when CPU temperature hit a low spot (+- 52°C), but it also happened when I had CPU temperatures pretty high (> 70°C).

I guess the graphic chip would need reflowing, perhaps I'll bake it a time using my hot air gun at 450°C. But since the iMac G5 is working like 98% of the time I don't see the need right now.